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Is multitasking a myth?
Often, the term 'multitasking' is applied to very busy and 'wired' people.  There is an adage that women multitask better than men.
My question is, do we actually multitask?  If so, what are the cognitive processes that allow this?
Or, is it a case that we momentarily put a task on hold to do another and it has more to do with a well organised short term memory of tasks?

I think it depends on how you define multi tasking.  Certainly we can listen to words while we watch the mouth, processing two different streams and integrating them.  But if you play two different audio streams into the ears, most people can only focus on one of them at a time.  With a little bit of practice, one can pat the head as they rub the belly.  There was a study that showed that office multitaskers made significant  sacrifices to work quality.  Another study shows worse reaction times for drivers when they are on the cell phone.

@KeeganKeplinger I would be very interested in those studies - do you have links to them?  Thank you for this!

I can't guarantee that I'll have time to be more thorough anytime soon, or I'd make it an official answer with references.  If I find time, I'll do so, but I welcome anyone else to dig up the resources (I'd probably just go to google and/or google scholar myself).

+1 @KeeganKeplinger the answer depends critically on how you define multitasking. Depending on the definition it is either commonplace & essential, or illusory and impossible. For a relatively accessible 'cog sci' overview and theory/model see 'The Multitasking Mind' by Salvucci and Taatgen, or google those authors.

There are different types of multitasking, concurrent multitasking and sequential multitasking, which I outline here. And, there is also something called task switching which I detail further in the linked paper there.

Scientists studying the matter generally believe multitasking, and women's superiority at it, to be a myth.  Men come out slightly better multitaskers than women but there's not really any meaningful difference.  The way it's defined is critical though; it's being able to do two things that typically require focal attention at the exact same time.  For example, driving and carrying on an important conversation on the phone.  In general, people are quite bad at any such multi-tasking.
When you interview women they tend to believe the myth that women are better but it's based on a different definition of multitasking.  They often mean that they'll start one task that can sort of self run, like putting the laundry in, and while that's happening go and work on a letter they've been writing to a client or some other task.  They would tend to say they do that all of the time.  There's not much research into whether men or women are better at that because that's generally not the kind of multitasking researchers have cared about. I should think an investigation into planning potentially overlapping tasks would be how you'd test this.
In addition, as one of the articles below mentions, there seems to be a general belief that while neither sex is particularly good at it, women actually do it more frequently.  That too, hasn't really been studied as far as I know.
Here are some related newsy articles:
Why men (yes, men) are better multitaskers
Are Men or Women Better at Multitasking?

I like to think of multitasking as rapid task switching. See  Pashler's (2000) article for the implications of "multitasking."
References

Pashler, H. (2000). Task switching and multitask performance. To appear in
Monsell, S., and Driver, J. (editors). Attention and Performance XVIII:
Control of mental processes. Cambridge, MA: MIT Press

Anyone willing to summarize conclusions of paper ? :)

Here's the link to an interview to a Stanford researcher, Clifford Nass, where he answers questions about the topic.
http://www.npr.org/2013/05/10/182861382/the-myth-of-multitasking
Some links to one of his published research papers:
http://www.pnas.org/content/106/37/15583.short
(I recommend searching in Google Scholar for other papers by him, to the people interested in the topic.)
I quote a fragment from the interveiw which I consider very relevant to the question:

People who multitask all the time can't filter out irrelevancy. They
  can't manage a working memory. They're chronically distracted.
They initiate much larger parts of their brain that are irrelevant to
  the task at hand. And even - they're even terrible at multitasking.
  When we ask them to multitask, they're actually worse at it. So
  they're pretty much mental wrecks.
(LAUGHTER)
FLATOW: Wow. But they don't think they are.
NASS: No. You're...
FLATOW: And that's the danger, right?
NASS: That's right. No, they actually think they're more productive.
  They actually think they tend to - and most notably, they think they
  can shut it off, and that's been the most striking aspect of this
  research.
We - the people we talk with continually said, look, when I really
  have to concentrate, I turn off everything and I am laser-focused. And
  unfortunately, they've developed habits of mind that make it
  impossible for them to be laser-focused. They're suckers for
  irrelevancy. They just can't keep on task.

I think I read in some book or other, maybe called Mindfulness, by E.J.Langer (ISBN  0201523418), that William James (?) taught himself to write about one topic while discussing another topic.  However, he could not remember what he wrote about afterward, and the writing was not very compelling in any case.
I think it may be possible to do more than one thing at once, but not well.

I think we all multitask to some extent which is not just task switching. Such as while watching a movie, we watch the visual scene (containing multiple objects) , listen to the soundtrack (music + voice), perceive the theatre hall's airconditioner temperature, all at a time. I don't feel it is just a very fast task switching. Its just simultaneous processing of several sensory inputs.
Talking or thinking while walking is another example of multitasking.
Breathing is another example of multitasking, we continually do it even when we do any other work. (Breathing is partly a voluntary action, we have voluntory control over it).
However doing certain types of work together, may be difficult for some and not so difficult for someone else.
For example I know a tutor (male) who can solve chemistry problems over a paper while receiving a phone call about another chemistry problem.
My mother can listen to my words while she teaches music via phone and can interfere the student on other end of phone making a mistake.
I know several female teachers who can write something while listening to something else.

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What neurological processes occur with 'revulsion'?
As the title asks, what neurological processes occur when we feel revulsion?
By revulsion, I mean the involuntary and voluntary physical and psychological responses far stronger than the aversion discussed in this question to things like, in my case, cockroaches.  I assure you, that I am not referring to 'fear' either, I mean a feeling of loathing towards something.

A good way to start answering this question would be to find any journal paper at all on how revulsion is different from fear or aversion--that difference needs to be defined before this question can be answered.

I remember reading that disgust, even if social or visual, had a lot of overlap in activity patterns with the same circuits involved in physiological nausea.

@KeeganKeplinger that makes sense as that is definitely one of the sensations of 'revulsion'.

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What cognitive processes occur during a mental exhaustion or 'burnout'?
Mental burnout - or mental exhaustion is not very pleasant, when one feels completely overwhelmed, something 'snaps' and it is hard to concentrate and maintain motivation.  What are the cognitive processes that occur during a burnout?  What processes allow for recovery?

can you explain the "something 'snaps'" part please.

@GregMcNulty when 'something snaps' is when a person 'hits the wall' or essentially, reaches their limit and thereafter, motivation, energy etc levels drop.

Also related: What is the scientific basis for long-term negative physiological effects of overstudying? and
Is it possible to over burden yourself?

One of the older theories suggested that a person literally runs out of brain-fuel when they hit the wall (Baumeister et al, 1998). They called this state "ego depletion" and it refers to the kind of mental burnout you are talking about. There is currently a lot of research activity on this topic because we (psychologists) assumed for over a decade that some resource was depleted in the brain but have found no evidence for any such resource. Newer theories suggest that people go through a kind of motivational cycle in which people tend to approach longer-term goals with delayed rewards (e.g., doing homework) for some period of time, followed by pursuit of shorter-term goals with immediate rewards (e.g., eating, leisure, etc.; see Kurzban et al, 2013 for a great discussion).
Thus, people with high self-control are people who spend relatively more time engaging in "labor" and impulsive people spend relatively more time pursuing leisure. The cyclical nature of motivation has clear adaptive qualities and the burnout that you feel after working for long periods is thought to be your brain doing exactly what it is designed to do: keep you from neglecting short term goals which are/were just as essential for survival as long-term goals. This is in direct contrast with the brain-fuel idea, which models burnout as self-control failure. See the Inzlicht article for a critique of brain-fuel models.
One interesting area of work that is related to all of this comes from the ADHD literature. The drugs developed to treat ADHD have demonstrated a clear connection between dopamine activity in the frontal lobes and the ability to persist in pursuing labor goals. It might be tempting to think that dopamine is the phantom brain-fuel we've been looking for, but note that the brain has no problem producing dopamine (i.e., it doesn't "run out"). Nobody has really pursued this, but it will be interesting to see how psychologists integrate the role of dopamine and frontal lobe functioning into self-control models. The Barkley reference below is an old one, but it is a good review of ADHD research that is relevant to this topic.
Barkley, R. A. (1997). Behavioral inhibition, sustained attention, and executive functions: constructing a unifying theory of ADHD. Psychological bulletin, 121(1), 65.
Baumeister, R. F., Bratslavsky, E., Muraven, M., & Tice, D. M. (1998). Ego depletion: is the active self a limited resource?. Journal of personality and social psychology, 74(5), 1252.
Inzlicht, M., Schmeichel, B. J., & Macrae, C. N. (2014). Why self-control seems (but may not be) limited. Trends in cognitive sciences, 18(3), 127-133.
Kurzban, R., Duckworth, A., Kable, J. W., & Myers, J. (2013). An opportunity cost model of subjective effort and task performance. Behavioral and Brain Sciences, 36(06), 661-679.

I guess the bottom line is that we now believe that burnout is a motivational shift that occurs when spending too much time pursuing labor goals. Not a loss of motivation. How much labor is too much? It probably depends on genetic predispositions and the environments in which people acquired their goals.

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What are the cognitive and neurological bases for apathy?
Apathy, or effectively the feeling of "not caring" or putting it colloquially, "not giving a rats", is something that most of us get sometime or another in varying degrees.
My question is, what are the cognitive and neurological bases for apathy?  Why is it that some experience it far stronger and more often than others?

From look at the research I don't think anyone in psychology and neuroscience cares. :)

@JohnChristie very punny, ha ha ha... but, you may actually be on the money there.

You might find some relevant/related information under "flat affect"--which looks a lot like not giving a rats!

Assuming the original poster (now departed) was considering apathy as a distinct phenomena from depression, then current evidence points to the current neurological basis of apathy being connectivity in the pre-motor brain systems according to "Individual Differences in Premotor Brain Systems Underlie Behavioral Apathy" by Bonelle et al. (2016):

The results demonstrate that behavioral apathy is associated with
  increased effort sensitivity as well as greater recruitment of neural
  systems involved in action anticipation: supplementary motor area
  (SMA) and cingulate motor zones. In addition, decreased structural and
  functional connectivity between anterior cingulate cortex (ACC) and
  SMA were associated with increased behavioral apathy. These findings
  reveal that effort sensitivity and translation of intentions into
  actions might make a critical contribution to behavioral apathy. We
  propose a mechanism whereby inefficient communication between ACC and
  SMA might lead to increased physiological cost—and greater effort
  sensitivity—for action initiation in more apathetic people.

Note that the authors of the paper controlled for depression using questionnaires:

Self-reports of apathy traits were obtained using a modified, extended
  version of the original Lille Apathy Rating Scale (LARS-e), available
  online in Bonnelle et al. (2014) (see Supplementary Material for more
  details). The LARS-e uses subscales that allow assessment of apathy
  traits along several domains reflecting the distinct component of
  apathy (behavioral, cognitive, and emotional). We used the “Action
  Initiation” (AI) subscale of the LARS-e, which measures every-day
  productivity and initiative and is an index of behavioral apathy
  (Sockeel et al. 2006). This subscale was previously found specifically
  to relate to the willingness to engage in an effort response in order
  to obtain a reward on our paradigm (Bonnelle et al. 2014). In
  addition, to control for a potential confound of depression and
  anhedonia, we also used the Depression, Anxiety, Stress Scales (DASS)
  (Lovibond and Lovibond 1995), a questionnaire developed in nonclinical
  populations to measure depression, and the Snaith–Hamilton Pleasure
  Scale (Snaith et al. 1995), which assesses anhedonia.

The authors assessed patients according to their willingness to complete a task while stakes (a combination of expected reward and expected effort) were manipulated. They found a high correlation between sensitivity to effort and behavioural apathy as assessed via the questionnaires in the previous quote. They then examined connectivity via fMRI of the patients completing the task and determined certain areas were more connected in patients with lower behavioural apathy. Specifically, the pre-motor brain systems were better connected in non-apathetic individuals.
It's unclear what this means cognitively, but the authors hypothesize, based on other activation, that this: "might be due to higher 'subjective experience' of effort cost in individuals who are more apathetic".

In some cases, Apathy descends from dissatisfaction one has faced in his own life. An apathetic would generally be a man whose own desires to be loved have not been sated in the past. Generally such a person doesn't give a damn when he comes across someone in need.
Somehow he convinces himself "When nobody paid heed to me when I needed help, Why should I help anyone?". And as we all believe, We become what we repeatedly do. Thus, voice within him that guides him to help others goes on to become weaker and weaker.
Others, I suppose are too engrossed in fulfilling their own goals and pursuing their own interests that they don't have scope left to look into others' lives and their problems.

I like the logic of this, it is prefered if you can offer some researched evidence to support ideas on this particular [se] site. cheers


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Can we change our personalities?
In psychology, a difference is made between personality attributes as a state or as a trait. For example, a usually outgoing and sociable person might find himself uncommonly shy in the presence of a woman he finds attractive. He is not shy "by nature", but only in this situation – his momentary shyness is a state. Another person, on the other hand, might be generally timid around even close friends and family members – his shyness is a trait.
Can this person, who is always and basically shy, decide to change himself and not only learn to overcome his fear, but really and truly become extroverted from the ground up?
Shyness is just an example here, I'm not interested in therapies for shyness, but in basic deliberate personality changes that take place within a reasonable period of time (a few years, not half a lifetime).

Generally, I would like to see some more published research on this topic.

@what Well, the published research is not going to phrase things as "traits," it's always going to use something like "SAD" for shyness.  I was trying to think of other ways that they could represent other traits, but the good research is usually only funded when it investigates some sort of pathology.  I did give you 7-8 published, peer reviewed, FRESH, (1 of them hasn't even been published yet, a few others published this week) research though.  However, do you have any other examples of a "trait" that would need fixing?  Aggression, addiction...?

You won't find much more research on other methods that arn't as proven.  I'm not trying to get points either, I'm just trying to be honest.

@what As I explained, you won't find any research on the topic as you framed it as the question disappears once you clarify some key concepts and boils down to asking whether there is any stable trait. If you fail to explicitly state what counts as “personality” for you or specify what personality traits you are interested in, this is simply not amenable to empirical research.

@GaëlLaurans To me, I feel he comes across clearly in that he does attempt to distinguish between "personality" traits within a situational context and within a global ("from the ground up") context.  He also uses an example as to what would count as personality to him, which is "shyness."  I think one can accurately hypothesize other personality traits, according to his definition and example, that are similar to that one without him having to make a big list.  Ideally research asks and answers a specific question, but sometimes its not what you wanted - thus you extrapolate.

@GaëlLaurans Essentially, I believe you may be breaking down the question into smaller pieces than I've broken other ideas down to before.  We all know there are many, many variables that are in play, but I believe "What" ("What"  meaning the author of the question) is looking for averages and levels of significance of variables rather than looking at each data point individually, which can inflate the noise/signal ratio.  "What", If this is incorrect, please let us know.

This is my opinion, based on what I know about how the brain works. As all process within the brain are physiological processes. It must be acknowledged, that what we know now about the brain, will, most likely, seem simplistic, to future generations; as more research is done. Will provide some quotes from the links I've provided, as I have time.

I don't wish to get bogged down in a debate about what “personality” is, traits, state etc. For the sake of this argument, let's assume personality is the most "natural" way of being of a person. Those innate impulses that arise from the "subconscious" parts of the brain, and these can either be allowed to flow (depending on social context and impulses) or require vigorous conscious action by the frontal lobe, to inhibit action upon such impulses. This latter comment regarding inhibiting these does not pertain to the actual “personality”, but to the efforts required to make conscious change and is a measure of the difficulty in bringing about fundamental personality change.
So for the purpose of this argument, I am viewing personality as the subconscious impulses that arise from the brain.
Which then brings us to the question. What is causing these impulses? To make it short, Long Term Potentiation) LTP of various neural pathways within the brain.  There is no guarantee that a connection between two neurons will fire. It is the priming of the synaptic cleft , the membrane endings and contents of both neurons that increases the likelihood that the a connection will form between two neurons. When a pathway is formed, that is “permanent” (as close to permanent as something can be in the brain), it means that pathway of the brain has been Long Term Potentiated. So the neurons fire to form that thought/action/feeling, effortlessly and reliably.
Which brings us to the next question. How is the brain Long Term Potentiated? To make it short (again), for “ordinary” activities; like learning the piano, or not to interrupt people when they are talking; reiteration of experience. The more dull the consequences of each iteration, the more iterations required.  Which works, conversely, as in the case of trauma, where there is a cascade of chemicals throughout the body that assists in the LTP of the neural paths being used during the experience.
This then brings us to the next question. How does change one's personality or one “undo” or “reduce” LTP of parts of the brain, we’d like to change and bring about “LTP” of pathways in the brain we find desirable. Now this is the key to answering the OP’s question, Can personalities change within a period of a few years (as opposed to decades).
As already mentioned in one answer, well-practiced psychotherapy (whatever you’d like to call it) relies on the concept of undoing LTP and LTP different pathways. Also, as mentioned in another answer, trauma creates a rapid change in LTP of pathways in the brain.
Now, I say this, using the logic of my above points; From my observation of human beings, my own efforts in life to change my personality and study of neuroscience and interest in psychology and psychiatry. I can honestly say, I have come to the conclusion, that it is most difficult and unlikely that any significant change can be made to someone’s personality, without the use of severe methods. One can practice overcoming (in this case), the action of behaving as a shy person, but the experience of social anxiety will remain and lag. It will eventually change. As the brain is plastic and we can mold it through repetition. However it, usually, would take longer than a few years for the internal changes to follow. This is something that can be achieved over half a life time, but the outward change of behavior, does not equal an inward change of personality; it can be a reflection of a person’s willingness to bring about change (and is most certainly a step in the right direction in achieving change). Look at many disciplines, martial arts, many spiritual vocations, it takes many years for the person to evolve. Which is a change in personality. And in these cases this is people living a full-time existence to transform their personalities. So the poor, every day, folk, with all of life’s pressures bearing down upon them, it makes it even harder to consciously override our natural impulses.
I should add, that it's the gamut of human experience that shapes who we are, combined with the natural chemistry. I have not covered this as in depth as would be to give this discussion full due.
As this site is a minefield of potential controversy and arguments over semantics. For the purposes of this answer I am using “words” that I am defining for the use of this passage here, and the debatable semantics of their use is outside of the scope of the OP’s question. So please comment on the merits and principle of my answer, that addresses the question and not points off topic.

BEHAVIORAL AND BRAIN SCIENCES (1997) 20, 597–655
Long-term potentiation: What’s
learning got to do with it?
Tracey J. Shors
Louis D. Matzel
http://hargreaves.swong.webfactional.com/bbs97.pdf

Can you give some references for your claims? E.g., is this your personal definition of personality or does that come from the literature? What's the evidence regarding the time scale of neuronal changes? Also, it seems to me that you have proposed a mechanistic explanation of how personality changes might occur on a microlevel. But with regard to the question wether it can be changed you provide little evidence except your own opinion.

Skippy, I like your passion here, and appreciate that you've turned it into well-referenced answer, but I think establishing a link between LTP and personality might be Nobel worthy, so I think your conclusions are a bit too far-reaching.  I think if you preface the question with your disclaimer, it might be better.

I'm definitely not discouraging anyone from answering questions, it's just that it took decades (and in some ways, work is still being done) to show that LTP and learning were intimately related.  You may turn out to be absolutely correct in making the leap from synaptic plasticity to something as abstract as personality, but it's a big step.  The emphasis that you've now added on the speculative nature will help someone who may not be steeped in LTP at all make sense of what you are trying to say was more my point.  Not picking on you for sure, so keep up the good work.

Skippy: Thanks for adding the reference. Not only do I personally find it interesting, but I think your post is much more usefull now. I would also like to thank @Chuck Sherrington, because he managed to express the concerns that I had as well in a very good and constructive way.

@Skippy My response, well it's rather simple. In life, we are all 50% right and 50% wrong in a debate. However, when it comes to one's beliefs, who is it to say that you or I are incorrect? Who's inside WHO'S brain anyway? W&G

The real question here is whether traditional personality dimensions have such a big influence on behavior as usually thought or, perhaps, if there is such a thing as being “really and truly extroverted from the ground up”. Once you begin to admit that circumstances play an important role or that personality traits are fuzzy types, being “truly extroverted” becomes rather vague.
Of course, it could be said that, by definition, personality cannot change so quickly but that would not be a very interesting statement. Empirically, there is no such thing as being shy “by nature” outside of a situation, you can at most observe a series of shyness-related behaviors in a range of situations. What is interesting is to determine what exactly is stable across time and situations.
If you look at things that way, “Is shyness impossible to change?” is possibly a tractable question but statements about personality changes in general are mostly empty.
Note that talking about “personality states” extends the notion of personality to the point of uselessness. The debate about traits and states in psychology could rather be seen as a debate about the existence of some commonly posited personality traits and the way to measure them (e.g. if people fill in personality scales based on their mood instead of some stable characteristics, there are simply no “traits” to speak about, no matter how you formulated the instructions to your questionnaire).
One reference on this:
Allen, B.P., & Potkay, C.R. (1981). On the arbitrary distinction between states and traits. Journal of Personality and Social Psychology, 41 (5), 916-928.

"Empirically, there is no such thing as being shy “by nature” outside of a situation". But of course there is! Some people are more shy than other people across all situations. People are not the same, they do have differing personalities! (Please not that with "by nature" I do not imply that a trait is necessarily inborn. It might be, and the answer to my question might depend on it.)

This is just you grouping a number of observations under the concept of shyness. Each individual behavior you observe is necessarily in a situation, personality is not something that is immediately observable. How meaningful it is to group them is the question. Besides, what do you imply by “by nature”, then?

"by nature" = trait (over all situations) vs. state (in special situations)

I think shyness is not a good example, because I don't know if there is a reliable instrument to measure it. But let's take depressivity. Theoretically we can assume that depressivity = trait depr. + state depr. Now you can measure many different persons in many different situations. If you find that one person has lower than average depr. over all situations, then what you see is the effect of trait depr. I was of the opinion that such traits that differ between people have been shown to exist. Behavior is not only situational. My question is: can you change the trait underlying it in part?

A state would be depression or sadness, not “depressivity” but averages and rating scales simply hide the variability by construction, this is not really helpful to settle the debate. Anyway I am not interested in a speculative discussion and I did not express any opinion about personality traits, I just offered some thoughts on how to approach this in a more productive way. It seems that questions about “changing traits” in general or language like “truly become extroverted” just muddle the problem.

@Skippy Thanks! I tend to think that a lot of confusion and (pseudo-)debates in psychology and cognitive science (not only on this site) result from the careless use of common sense concepts and simply reduce to an argument about (unstated) differences in definition which are completely devoid of empirical content and ultimately not very interesting. That's why I often end up dissecting questions rather than answering them on their own terms and post more comments than actual answers on this site.

As promised, here is an elaboration of my comment.
As you mentioned, what, in one of your comments, environmental factors come into play.  A particularly traumatic sequence of events resulted in me making a few changes, and a few changes being made anyway.  Basically, several personality traits vanished (both positive and negative ones) and were replaced.  This took place over a period of a few years.
A lot of it is 'self-training' - through events around me and my own decisions, certain personality traits were 'trained' into others.  Some, I just simply 'grew out of'.
When the same situation resurfaced, I approached it in a very different way.
A term that describes the personality change that occurred in me, and happens to a lot of people is 'hardening up', in my case, the 'sympathy-seeking' part of my personality became a resilient part... but this also resulted in my 'sympathetic' part of my personality to become a more pragmatic aspect (where I do what is needed, but don't verbalise the sympathy).

Thank you. This is very helpful. What strikes me the most is that from your description you were not simply dissatisfied with a trait of yours (or the behavior that followed from it) and decided to change it, but rather a trauma gave you the necessary persistence to not give up your "training" to become different. I have seen this often in alcoholics, who were able to overcome their addiction only after a traumatic experience resulting from their alcohol abuse. And I believe it is the reason why shyness and smoking are so hard to cure -- they rarely cause a trauma that could instigate change.

So your answer to my question would be: one needs a strong impulse, and then deliberate change is possible.

Yes, exactly that.

+1 very interesting answer, thank you

I'm surprised to see seven answers to this question and no mention of directly relevant theory on personality change thus far. Certainly some exists – though I sympathize with the first comment on the OP – and it's really not hard to find. The sixth current Google hit for "change personality" is a directly pertinent literature review by a prominent social/personality/developmental psychologist (Dweck, 2008), and its conclusion favors the feasibility of change in general. Dweck argues that beliefs and expectations are key factors in the process, particularly as they pertain to one's ability to change. This supports a popular aphorism: the surest way to fail is to not try.
Other answers of mine are worth referring to here:

This answer regarding innate personality incorporates a figure and discussion of how biological and environmental factors interact to change personality, which gradually "sets like plaster" over time.
This answer about neuroticism and neuroplasticity incorporates two figures depicting personality change over time, and cites theory that summarizes these changes as positive and more rapid in young adulthood. Thus intentional change may require less time if one starts relatively early.
This answer about social desirability suggests the general factor of personality may be driven by intentional realignment with social demands. I should probably add some references here!

This is just the bare skeleton of an answer to what is potentially a very broad and deeply controversial question. Much more can be added if you wish. For instance, strong evidence of biological factors in extraversion implies that some substantial amount of individual differences in this trait are relatively immutable, so it may be quite unlikely that an always-basically-very shy individual would become truly "extroverted from the ground up"...though in the spirit of Dweck's answer, I would never call this or any other form of self-motivated growth impossible.
BTW, more of those Google hits are also worth citing here:

Hit #5: Psychology Today has a nice section organizing personality change articles, including:

A review of a study of short-term personality change resulting from international travel
An article on relatively more concrete life choices that probably affect personality somewhat
An article on traumatic experience, recovery from which is important in personality development
An article about personality change from the perspective of a significant other

Hit #7: Wikipedia on personality changes, some of which result from social role choices
Hit #8: Wikipedia (again) on changes in personality over the lifetime, some of which is fairly rapid
Hit #10: Dan McAdams on personality theory, levels, and change (a 5-minute video)

Reference
Dweck, C. S. (2008). Can personality be changed? The role of beliefs in personality and change. Current Directions in Psychological Science, 17(6), 391–394. Retrieved from http://www.psychologicalscience.org/journals/cd/17_6_inpress/Dweck.pdf.

Up until recently, no empirical research has directly addressed this question. However now, there is first, initial evidence that people may indeed be able to change their personalities intentionally.
Hudson and Fraley (2015) have investigated this possibility with two longitudinal studies.
How did they study this question?

In the beginning, they asked participants to indicate their goals to change with regard to the big-five personality traits
They tracked personality changes of undergraduate students over the course of 16 weeks
Half of the students were randomly assigned to an intervention intended to help them to make small changes in their daily lives that would translate into crystallized personality changes. To do so, they asked them to indicate and plan ways to achieve their goals.

What did they find out?

People had, on average, goals to change their personality traits
People's initial goals predicted changes in the desired direction. For example, people who wanted to become more extraverted, did indeed become somewhat more extraverted as the study progressed
In the first study, the intervention had no effect. However, the authors observed that participants had described very vague plans to change their behavior. Therefore, they instructed them to form very concrete behavioral plans (so-called implementation intentions) in the second study. This time, the intervention led to more personality change in the desired direction.

Caveats

The changes were modest (.05 standard deviations per month)
The research is based on self-report measures. Thus, participants self-reported their personality with a questionnaire measure. Therefore, the observed changes may, to some extent, be biased (because of the desire to change, or the desire to conform to the implied expectations of the researchers).

References
Hudson, N. W., & Fraley, R. C. (2015). Volitional personality trait change: Can people choose to change their personality traits? Journal of Personality and Social Psychology, 109, 490–507. doi:10.1037/pspp0000021

Similarly to what CPTED is based on, referring to the environment being what defines behavior, I wouldn't think an individual can decide to change his or her personality.
Just as in your example of "turning shy" due to an environmental stimulus, any situation that would trigger the need or want to "change personality" must originate from the environment too.
The individual could, however, learn to perceive itself as being extroverted depending on the environment even if he's doesn't recognize the cause of this change being external.
The quickest way would probably be through therapist though.

All emotions and behaviors are caused by both the environment and the personality of the individual. You can deduce this double influence from the fact that different people will behave differently in the same situation, and that one single individual will behave differently in different situations. You can change behavior by changing the environment. But that way the individual will fall back to his old behavior, once he encounters old situations. That's why drug addicts relapse. Once they return to their old circle of friends and their old problems, their old habits kick in. [contd.]

[contd.] The other option would be to change the individual. That way he would not be the same, when he encountered his old problems, and not behave in his habitual manner. That is what my question aims at. The need to change comes from a misfit between environment and individual personality, of course.

The individual is changed for any practical purpose when changes in his beliefs or brain chemistry make it experience the environment in a different way. so "old problems" can appear as "new problems" with a more desirable outcome between "environment and individual personality". In any case this cognitive change isn't something that the individual spontaneously "decides", even a situation where the individual is "told how to self-change" would be end up being an event out of the scope of his "decision".

No love for Jung yet :)
This depends on where we define our personality. If it's defined as our mask, our ego, then it would be almost as simple as changing shoes, for some people. If we define it instead as the self, centered in the brain and guarded by a great many layers of the mind, then I'd offer we cannot change them but that they can be changed through experience.
Stemming from the conflict between the ego and the shadow archetypes, whatever parts of our personalities we do not demonstrate in life become relegated to the shadow. Negative impulses, what we abhor and the things we reproach with unreasonable fervor. In this light, our choice to exhibit sides A, B and C of our selves but repress side D might seem like we are affecting our personalities in an impacting way. Jung states that this is not so.
Those parts of our personalities, the self, that we do not own, take on a sort of life of their own. The naturally shy person who makes a headstrong decision to extravert (ego taking control) with little to no outside stimulus is simply repressing their shyness. Note that shyness is not inherently a "negative" trait: read The Perks of Being a Wallflower. Instead of assimilating and digesting that portion of the personality, the shyness becomes beaten back and called "bad." Since it's undesirable in one's self, that will carry through to noting it in others and still considering it undesirable. This is what leads to the unreasonable reproach. The person does not wish to identify themselves with the trait of shyness, it may be seen as a sign of weakness or them not being "in total control" of their person. Yet they are shy. Their shyness will not be seen as theirs, it'll be launched onto others in a process known as projection. That will cause the persons to misplace their feelings of rejection (I should not be shy) and instead find fault with others who don't make the same decision they did (why can they be shy? It's a weakness, not acceptable).
I am like-minded with other answers here in that I believe the personality is, at least in part, a summation of our experiences. That's due to both the dance between ego and shadow formation, and just what we experience. Only so many choices of how to experience are within our hands (ie. glass half full or half empty; perspective). We don't often get to choose what to experience. If the person's shyness is a product of X or Y, then running across X and Y again may just reinforce it (my siblings talk over me, it's easier to keep quiet). However, if it's personal choice then all one would need to do is make the contrary choice and gain experiences to compound that (habit building, neuroplasticity, etc.). Either situation will require the latter, for reasons well illustrated by answers already posted here.
TL;DR
We can make conscious decisions in the short run to alter our personalities. However, it's a decision made by the ego and doesn't reflect the true self. Our shadow will correct for this and bring us back to our true selves; for better and for worse. The ego does not have complete control.
Since experiences compound to help shape who we are and our habits, taking new experiences can aid the person wishing to acquire another personality trait, or the contrary one (extraversion versus shyness). I'm not sure we're perfectly plastic though, especially the older we get. In many ways that's a good thing: I know many who, once they knew a little bit about PCs, proceeded to "fix" many things and just ended up buying a new one after several failed reboots. We don't have that option; the auto-regulation inherent in our minds is our last resort. The shadow is our most honest friend, telling us about our selves.

"I'd offer we cannot change them but that they can be changed through experience."  In trying to change mine for so long, I can tell you it is the accumulation of both of these things.  Not either or.  Taal. "In Response to Comment About Changing One's Personality only Through Experience: A Case Report." Cogsci Stackexchange 3 p 235 Aug 25th 2013.

@Taal I'm interested in your perspective. Would you care to share an answer of your own? I'm not convinced.

I couldn't fit my response in this space, so it's an answer.

@LitheOhm interested in your response.

@Taal if you're interested in arguing Jung, I'm a poor candidate for an opponent. You might try someone with more experience.
That wasn't quite what I was getting at in my answer. Without malice from I to you: let the votes speak. I do like Jung and won't change my answer.

@LitheOhm I didn't intend for you to, everyone's opinions are appreciated and debate is necessary to get to the truth.  You asked me for a response though so I gave you a response, that's all.

@Taal not quite what I meant, but fair enough. On debate: I'm only an amateur Jung fan, a hobby here and there. The worst thing you can do for a cause is poorly represent it. I do hope someone better versed in Jung than I can drop by and address your assertions against his structures, though.

@LitheOhm To be transparent I actually know nothing about Jung besides what I gathered from your post and his wikipedia picture + a little bit of wikipedia reading.

@LitheOhm I went and learned more about Jung...it got pretty creepy when he got into the Red Book.  I think he may have had undiagnosed schizophrenia or something.  Remember, it was around the 1900s.  You can go read a small piece of his Red Book (which costs $150 on Amazon) at http://www.npr.org/templates/story/story.php?storyId=120129676   after you read that though you should go read DMT & Datura trip reports over at http://www.erowid.org/experiences/subs/exp_DMT.shtml & http://www.erowid.org/experiences/subs/exp_Datura.shtml.  See if you can find any similarities.

Let's just replace the word shyness with "depression" for a second, just for example's sake.  You can easily switch them out with agressiveness, anxiety, shyness, whatever you want later.
"Because depression has been viewed as an emotional disorder throughout the
history of psychiatry, therapists from most schools of thought place a strong emphasis
on “getting in touch” with your feelings.
The research I've come across reveals the unexpected:
Depression is not an emotional disorder at all! The sudden change in the way you feel
is of no more causal relevance than a runny nose is when you have a cold. Every bad
feeling you have is the result of distorted negative thinking. Illogical pessimistic
attitudes play the central role in the development and continuation of all your
symptoms.
Intense negative thinking always accompanies a depressive episode, or any painful
emotion for that matter. Your moody thoughts are likely to be entirely different from
those you have when you are not upset. Here's an anecdote I found:

"Every time I become depressed, I feel as if I have been hit with a
  sudden cosmic jolt, and I begin to see things differently. The change
  can come within less than an hour. My thoughts become negative and
  pessimistic. As I look into the past, I become convinced that
  everything that I’ve ever done is worthless. Any happy period seems
  like an illusion. My accomplishments appear as genuine as the false
  facade for the set of a Western movie. I become convinced that the
  real me is worthless and inadequate. I can’t move forward with my work
  because I become frozen with doubt. But I can’t stand still because
  the misery is unbearable.

You will learn, as she did, that the negative thoughts that flood your mind are the
actual cause of your self-defeating emotions. These thoughts are what keep you
lethargic and make you feel inadequate. Your negative thoughts, or cognitions, are the
most frequently overlooked symptoms of your depression. These cognitions contain
the key to relief and are therefore your most important symptoms.
Every time you feel depressed about something, try to identify a corresponding
negative thought you had just prior to and during the depression. Because these
thoughts have actually created your bad mood, by learning to restructure them, you
can change your mood.
You are probably skeptical of all this because your negative thinking has become
such a part of your life that it has become automatic. For this reason I call negative
thoughts “automatic thoughts.” They run through your mind automatically without the
slightest effort on your part to put them there. They are as obvious and natural to you
as the way you hold a fork.

The relationship between the world and the way you feel. It is not the
actual events but your perceptions that result in changes in mood. When you are
sad, your thoughts will represent a realistic interpretation of negative events. When
you are depressed or anxious, your thoughts will always be illogical, distorted,
unrealistic, or just plain wrong.
If your understanding of what is happening is accurate, your emotions will be
normal. If your perception is twisted and distorted in some way, your emotional
response will be abnormal. Depression falls into this category. It is always the result of
mental “static”—distortions. Your blue moods can be compared to the scratchy music
coming from a radio that is not properly tuned to the station. The problem is not that
the tubes or transistors are blown out or defective, or that the signal from the radio
station is distorted as a result of bad weather. You just simply have to adjust the dials.
When you learn to bring about this mental tuning, the music will come through clearly
again and your depression will lift.
You may experience a pang of despair when they read that
paragraph. Yet there is nothing upsetting about it. If anything, the paragraph should
bring hope. Then what caused your mood to plunge as you were reading? It was your
thought, “For other people a little tuning may suffice. But I’m the radio that is broken
beyond repair. My tubes are blown out. I don’t care if ten thousand other depressed
patients all get well—I’m convinced beyond any shadow of doubt that my problems
are hopeless.” I hear this statement fifty times a week! Nearly every depressed person
seems convinced beyond all rhyme or reason that he or she is the special one who
really is beyond hope. This delusion reflects the kind of mental processing that is at
the very core of your illness!
I have always been fascinated by the ability certain people have to create illusions.
As a child, I used to spend hours at the local library, reading books on magic.
Saturdays I would hang out in magic stores for hours, watching the man behind the
counter produce remarkable effects with cards and silks and chromium spheres that
floated through the air, defying all the laws of common sense. One of my happiest
childhood memories is when I was eight years old and saw “Blackstone—World’s
Greatest Magician” perform in Denver, Colorado. I was invited with several other
children from the audience to come up on stage. Blackstone instructed us to place our
hands on a two-feet by two-feet birdcage filled with live white doves until the top,
bottom, and all four sides were enclosed entirely by our hands. He stood nearby and
said, “Stare at the cage!” I did. My eyes were bulging and I refused to blink. He
exclaimed, “Now I’ll clap my hands.” He did. In that instant the cage of birds
vanished. My hands were suspended in empty air. It was impossible! Yet it happened!
I was stunned.
Now I know that his ability as an illusionist was no greater than that of the average
depressed patient. This includes you. When you are depressed, you possess the
remarkable ability to believe, and to get the people around you to believe, things
which have no basis in reality. As a therapist (author), it is my job to penetrate your illusion, to
teach you how to look behind the mirrors so you can see how you have been fooling
yourself. You might even say that I’m planning to dis illusion you! But I don’t think
you’re going to mind at all.
Read over the following list of ten cognitive distortions that form the basis of all
your depressions. Get a feel for them. I have prepared this list with great care; it
represents the distilled essence of many years of research and clinical experience.
Refer to it over and over when you read the how-to-do-it section of the book. When
you’ are feeling upset, the list will be invaluable in making you aware of how you are
fooling yourself."
Taken from From David Burn's Book:
"Feeling Good, the New Mood Thrapy."
Which you can buy for $5 to your Kindle, Computer, Kindle iPhone App, or anything else. by going here:
http://www.amazon.com/Feeling-Good-The-Mood-Therapy/dp/0380810336
Alternatively you can view an abbreviated version of the thinking errors he speaks of by going here:
Have the core CBT "Thinking Errors" been found to NOT be effective in evidence-based clinical practice?

**Part of this is a response to @LitheOhm 's question, but is still highly targetted towards the original question with actionable steps as well.
@LitheOhm
I couldn't fit my response into a comment so I had to post it as an answer, although it does answer the question quite well...and I'm getting my citations right now.
Correct me if I'm wrong on any of my interpretations.  Also any hostility is not directed towards you, but is towards Jung and associated theories.  Please keep this in mind.

1st Clarifying Your Definitions

"If it's defined as our mask, our ego, then it would be almost as simple as changing  >shoes, for some people."

I'm assuming here that you mean putting on a fake persona that doesn't necessarily reflect how one feels about whatever situation they are in or task they are doing.  For instance, someone who is in sales has to put on this "persona" to sell more stuff or acting happy when you are talking to someone on the phone you don't really want to - or even just being polite perhaps.  You'd say this is a "mask."  I'd agree with you.  People's "outer" (I'll try not to throw more semantics in after that word) personalities change to adapt to whatever situation they are in.  You then say this mask = the ego.

If we define it instead as the self, centered in the brain and guarded
  by a great many layers of the mind, then I'd offer we cannot change
  them but that they can be changed through experience.

Now you're getting a little confusing with the pronouns not to mention a bit of "poetic psychology."  Who or what is we is "we"?  You don't define this clearly so I'm going to see if I can get at what you're saying:
Your use of "we":  Is it the ego?  Is it our thoughts?  Is it anything we do with our mind?  I'm going to assume here (only because of prior knowledge) that when you say "we" you mean the ego, which would include our mind and the thoughts of our mind. Is this correct?
**I'm gonna skip ahead and go ahead and also assume you don't mean ALL thoughts.  You'd just mean "conscious thoughts"  Why?  Because there are unconscious thoughts too, but are those even thoughts? - I think you'd agree with me that these are more related to the "self" if not ARE the "self"/our personalities.
I'd also assume that "the great many layers of the mind" are also the "ego."  In essence, you're phrasing it as these layers (or conscious thoughts) trying to protecting the self when it feels threatened.  Is this correct?
So "we," which is also the ego if my interpretation is correct, is our mask, our mind, and our conscious thoughts essentially. They are all intertwined together within the "ego." Please correct me I'm misinterpreting things.

2nd Attempting to Reconstruct Your Statement
So would you mind if I replaced the word "we" in your statement with "conscious thoughts" due to my proof using my interpretation of your words?  Again, if I'm incorrect anywhere let me know.
Now your statement would be as follows - I added a bit of clarification in parenthesis:

"then I'd offer our conscious thoughts cannot change
  them (our personalitie(s)/self, which we do not own) but that they can be changed through experience(s)."

Simple enough.  We just have to have these experiences happen to us.  But when will they?  Will they ever?  What if I want to fix them?  Am I just screwed?
Hmmmm....Can we make choices that improve our odds of encountering these experiences which will change our personalities/self? Well, choices involve conscious thought and most likely the use of "we" at some point so technically we can't, at least according to the statement.
Since in reality "we" can make "choices" that lead to "experiences" your statement is already false, but...you could still say...
Even if we did make some choices to "try" to do this, we'd have very limited choices anyway. Right?  Not to skip ahead but you say later on you say:

"We don't often get to choose what to experience."

Oh, you DON'T?  Let's say someone puts a gun to your head and says "if you can list at least 150 choices in notepad you could make and or do right now instead of reading this dude's post, I'll let you go....and you get to meet Justin Beiber." Could you do it?  I could, and I'm not even a fan of his.
Thing is...
YOU HAVE UNLIMITED CHOICES ON WHAT YOU WANT TO DO WHENEVER YOU WANT.
Some choices may be bad, some may be good, but most you probably don't know the outcome to.
 You could run across the street naked which leads to you meeting your future mate.  You could go throw water balloons at people while driving your car around town.   You could read Stackexchange.   Play Everquest.   Go to the mall and try to pick up chicks. Pay for some "hot lovin" off Craigslist.   Collect Bitcoins.   Learn PHP.   Go to Thailand solely on your credit cards.   Join a meetup group.   Run away from home.   Punch mean kids in the face.   Choose to learn CBT.   Choose to believe you're not trapped by your ego and he is your friend, he just needs to be educated a little bit.   Choose to ask yourself why you're shy in the first place. Is there a reason?   Consider other strategies than just "trying to directly confront your shyness in the most cliche manner possible."

All of these are experiences which apparently you need to change your "self" or "personality" you'd have would of been made through purposeful conscious thought and the use of "we" - so you're statement = false assuming I did not misinterpret anything you said.

3rd Want to Change?  You Can.  Unless You Read Jung. Defeatist Attitude = Defeated.

"Those parts of our personalities, the self, that we do not own, take
  on a sort of life of their own. The naturally shy person who makes a
  headstrong decision to extravert (ego taking control) with little to
  no outside stimulus is simply repressing their shyness."

1) "that we do not own"

-Why don't we own them?
-Where did they come from?
-Are they really even there?
-Does example shy person have any sort of genetic defect that would cause them to be shy?
-Can said shy person think of any counterexamples he's seen before where someone used to be shy and then they weren't?

2) "naturally"

-Does this shy person have any friends at all?  Even one?  If so, is he shy around them?
-What causes this person to be naturally shy?  Just the fact that it's natural and that's how it's always been....any further reasoning?
-Are there different shades of naturally shy?  Or is it just black and white?  Maybe he's a light grey?
-If said shy person blames his parent's genetics for being shy, has he questioned the fact that maybe not EVERYONE in his entire family is also that way....I mean he has those genetics too.  I bet he has a crazy uncle.
-Has he ever considered environment vs. genetics or does he just accept his natural fate?  Yes, I know you mention this, don't worry - still not done.

3) "Who makes a headstrong decision to extravert (ego taking control) with little to no outside stimulus is simply repressing their shyness."
and later
  We can make conscious decisions in the short run to alter our personalities. However, it's a decision made by the ego and doesn't reflect the true self. Our shadow will correct for this and bring us back to our true selves; for better and for worse. The ego does not have complete control.**

-One big piece you're missing.  What if the person actually wants to overcome this trait?  I'll speak on that in a second.
-You seem to state this as a law of nature.  If someone has shyness deep within as their "self," they will keep it forever.  You leave no room for the potential of them overcoming it.  That isn't reality.  It's all or nothing thinking.  And the ego (which you seem to establish as conscious thought, a horrible thing) gives them choice.
-So it's always a bad idea to make a headstrong decision to be extroverted?  It doesn't matter HOW MANY TIMES you try - the shadows will ALWAYS bring you back?
-Is it possible the shadow doesn't exist?
-You state yourself that "with experience" you can change your personality...but here you state the opposite.  You contradicted the original statement we were discussing here.
-Has this theory been proven?
-Do you have citations that it's been proven with clinical studies in peer reviewed journals?
-Did they get this trait from genetics?  How many people have overcome genetic difficulties?
-Did they just "learn to be shy"?  If so, then why can't they "learn to be outgoing?"
-I know you're trying to get to the fact that this person should just accept their shyness.  Perhaps some people are content on that.
But what if they don't want to?  What if instead of an ordinary life (this is purely subjective of course), they want to maximize their potential and live it out the way they intended?  What about an extraordinary one?  Why are they letting Jung or whomever make the choice for them to accept this trait for the rest of their lives...why?....because Jung said so?
Ok Jung bring out your clinical trials of effectiveness in treating something - because we know nowadays that social anxiety can potentially be a root cause of depression.  Oh wait, there's really no therapy or application involved within...just theory...and acceptance.    Thanks Jung.  We appreciate your work that we built further upon and turned into practice....somewhat.  However, we have some better technology and therapy in today's world.  Please go back to 1875.
By the way, I did not see "Perks of Being a Wallflower" but it is not a citation of real life...it's a fictional story.  I've been a wallflower before.  A lot.  It's usually not fun.   But you know what? I've learned to overcome it, quite a bit....quite a bit.  I've also known many other people who have overcome it.  I've seen it.  I'm a human, they were human, anyone else reading this is human.  If I made progress, then why can't any other human?
Do you have another counterexample besides a fictional movie involving a statistical outlier (and a very strange one according to wikipedia)?

4th If This is Jung's theory...it has alot of assumptions

Instead of assimilating and digesting that
  portion of the personality, the shyness becomes beaten back and called
  "bad." Since it's undesirable in one's self, that will carry through
  to noting it in others and still considering it undesirable. This is
  what leads to the unreasonable reproach. The person does not wish to
  identify themselves with the trait of shyness, it may be seen as a
  sign of weakness or them not being "in total control" of their person.
  Yet they are shy. Their shyness will not be seen as theirs, it'll be
  launched onto others in a process known as projection. That will cause
  the persons to misplace their feelings of rejection (I should not be
  shy) and instead find fault with others who don't make the same
  decision they did (why can they be shy? It's a weakness, not
  acceptable).

My response:  Each sentence is an assumption based on no citations besides a fictional movie (which actually doesn't even support the assumptions).  There's not even an anecdote.  It seems to be written as an assumption wherefor the next sentence is also an assumption built on the previous assumption, wherefor, the next sentence is also an assumption build on the previous assumption that is built on the previous assumption.  Maybe this happens to a percentage of shy people?  But generalizing this is also breaking laws of reality.

5th One Final Contradiction
So the initial sentence I did not like was:

"I'd offer we cannot change them but that they can be changed through
  experience."

but then you say

"However, if it's personal choice then all one would need to do is make
  the contrary choice and gain experiences to compound that (habit
  building, neuroplasticity, etc.)."

I think the problem may just be in your definition of "we".  Because "we" are certainly doing things in your ladder quotation.

6th You CAN Use Thought to Change Your Personality: Cognitive Behavioral Therapy.

Picture from J Med Internet Res. 2013 Aug 5;15(8):e153. doi: 10.2196/jmir.2714.
The Clinical Effectiveness of Web-Based Cognitive Behavioral Therapy With Face-to-Face Therapist Support for Depressed Primary Care Patients: Randomized Controlled Trial. which is also cited way down below. http://www.ncbi.nlm.nih.gov/pubmed/23916965
I think originally this is what you were trying to say you couldn't do.  By saying "we" you were trying to say that the only way to change your "self" which is your "true personality" is by having experiences.
I believe in the experiences part, but I also believe, strongly, in the other part - changing the way you think - which I believe you would call the ego.  I also believe that they must be used at the same time for the best effectiveness.  One must have experiences and one must use those to fuel their CBT therapy, which they can just do by reading a book and writing their thoughts down, then writing a rational response next to it.
Nearly everything I said in this post was CBT based.  It simply asked about all the flaws in the theories Jung made.  This is exactly what you'd do with a thought like "those people don't want to talk to me because I'm so shy" if you were shy.  You'd start asking yourself (usually writing it out works best and is a core component actually) questions like:
1) How do they know that I'm shy?  And why does this even matter?
2) Have I, at ANY time in the past, ever been extroverted?  If so, why can't I do this again?
3) Why do I really even believe that I'm shy?  Do I have any sort of substantial backing for being shy...even if I was picked on in 2nd grade by all the kids - that doesn't mean anything today at all.
4) If you're shy you probably know alot of cool stuff cause you spend more time learning things than most people.  This gives you more content to talk about.
5) Let's say they just blow you off after you go talk to them?  How does that differ from where you were before? (Except now you actually have a bit of adreneline and serotonin coursing through your body - which you can use to have an even better conversation with the next people you may want to try to talk to.
6) Let me throw a twist in here.  Why shouldn't I just accept that I'm shy and that's it?  We'll because in today's job market unless you have some sort of specialized skill you need connections and you're going to need people skills sometime in order to survive.  Simply put, social skills are something you probably need.
I'm going to go ahead and post this while I fetch a barrage of clinical trials showing CBT's effectiveness for almost any disorder - which can be linked to a "personality" trait one may want to get rid of. They'll be alot of em'.
7th Answer: Use CBT Synergistically with Experiences/Exposure to Change Unwanted Personality Traits Quickly, Effectively, & Chronically.  It Does Require Work Though.
Try it now. Use this worksheet.
http://media.psychologytools.org/Worksheets/English/CBT_Thought_Record.pdf

Br J Psychiatry. 2013 Aug 22.
Treatment of child anxiety disorders via guided parent-delivered cognitive-behavioural therapy: randomised controlled trial.
  Thirlwall K, Cooper PJ, Karalus J, Voysey M, Willetts L, Creswell C.
  Kerstin Thirlwall, DClinPsy, Winnicott Research Unit, School of
  Psychology and Clinical Language Sciences, University of Reading, UK;
  Peter J. Cooper, DPhil, Winnicott Research Unit, School of Psychology
  and Clinical Language Sciences, University of Reading, UK, and
  Stellenbosch University, Matieland, South Africa; Jessica Karalus,
  MSc, Winnicott Research Unit, School of Psychology and Clinical
  Language Sciences, University of Reading, UK; Merryn Voysey, MBiostat,
  Centre for Statistics in Medicine, University of Oxford, UK; Lucy
  Willetts, MSc, PhD, Cathy Creswell, DClinPsy, PhD, Winnicott Research
  Unit, School of Psychology and Clinical Language Sciences, University
  of Reading, UK. Abstract BACKGROUND: Promising evidence
  has emerged of clinical gains using guided self-help
  cognitive-behavioural therapy (CBT) for child anxiety and by involving
  parents in treatment; however, the efficacy of guided parent-delivered
  CBT has not been systematically evaluated in UK primary and secondary
  settings. AIMS: To evaluate the efficacy of low-intensity
  guided parent-delivered CBT treatments for children with anxiety
  disorders. METHOD: A total of 194 children presenting with a
  current anxiety disorder, whose primary carer did not meet criteria
  for a current anxiety disorder, were randomly allocated to full guided
  parent-delivered CBT (four face-to-face and four telephone sessions)
  or brief guided parent-delivered CBT (two face-to-face and two
  telephone sessions), or a wait-list control group (trial registration:
  ISRCTN92977593). Presence and severity of child primary anxiety
  disorder (Anxiety Disorders Interview Schedule for DSM-IV,
  child/parent versions), improvement in child presentation of anxiety
  (Clinical Global Impression-Improvement scale), and change in child
  anxiety symptoms (Spence Children's Anxiety Scale, child/parent
  version and Child Anxiety Impact scale, parent version) were assessed
  at post-treatment and for those in the two active treatment groups, 6
  months post-treatment. RESULTS:
  Full guided parent-delivered CBT produced superior diagnostic outcomes compared with wait-list at post-treatment, whereas brief
  guided parent-delivered CBT did not: at post-treatment, 25 (50%) of
  those in the full guided CBT group had recovered from their primary
  diagnosis, compared with 16 (25%) of those on the wait-list (relative
  risk (RR) 1.85, 95% CI 1.14-2.99); and in the brief guided CBT group,
  18 participants (39%) had recovered from their primary diagnosis
  post-treatment (RR = 1.56, 95% CI 0.89-2.74). Level of therapist
  training and experience was unrelated to child outcome. CONCLUSIONS:
  Full guided parent-delivered CBT is an effective and inexpensive first-line treatment for child anxiety.

Cogn Behav Ther. 2011;40(3):159-73. doi: 10.1080/16506073.2011.576699.
  Epub 2011 Jul 20.
  Guided internet-delivered cognitive behavior therapy for generalized anxiety disorder: a randomized controlled trial. Paxling B,
  Almlöv J, Dahlin M, Carlbring P, Breitholtz E, Eriksson T, Andersson
  G.  Department of Behavioural Sciences and Learning, Swedish
  Institute for Disability Research, Linköping University, Linköping,
  Sweden. bjorn.paxling@gmail.com Abstract Generalized anxiety
  disorder (GAD) has been effectively treated with cognitive behavioural
  therapy (CBT) in face-to face settings. Internet-delivered CBT could
  be a way to increase the accessibility and affordability of CBT for
  people suffering from GAD. The aim of this study was to evaluate the
  efficacy of guided Internet-delivered CBT for GAD in a controlled
  trial with a wait-list control group. A total of 89 participants were
  included following online screening and a structured psychiatric
  telephone interview. Participants were randomized to either an 8-week
  treatment group (n = 44) or a wait-list control group (n = 45).
  Treatment consisted of a self-help program based on CBT principles and
  applied relaxation along with therapist guidance. The main outcome
  measure was the Penn State Worry Questionnaire. Ratings of clinical
  improvement and symptoms were included as well as secondary outcome
  measures dealing with anxiety, depression, and quality of life. Among
  the treatment group participants, 13.6% did not complete the
  posttreatment measures. The treatment group showed significant
  improvement compared with the control group on all outcome measures.
  Large effect sizes (Cohen's d > 0.8) were found both within the
  treatment group and between the groups in favor of the treatment on
  all outcome measures except on a measure of quality of life.
Results at 1- and 3-year follow-up indicated that treatment results improved or were maintained. The authors conclude that
  Internet-delivered CBT with therapist support can reduce symptoms and
  problems related to GAD.

Published last week.  Actually investigates and supports CBT therapy
through PHYSIOLOGICAL research and the way it changes the brain.

 JAMA Psychiatry. 2013 Aug 14. doi:
  10.1001/jamapsychiatry.2013.234. [Epub ahead of print]
Impact of Cognitive Behavioral Therapy for Social Anxiety Disorder on the Neural Dynamics of Cognitive Reappraisal of Negative
  Self-beliefs: Randomized Clinical Trial. Goldin PR, Ziv M,
  Jazaieri H, Hahn K, Heimberg R, Gross JJ.  Department of
  Psychology, Stanford University, Stanford, California.
  Abstract IMPORTANCE Cognitive behavioral therapy (CBT) for
  social anxiety disorder (SAD) is thought to enhance cognitive
  reappraisal in patients with SAD. Such improvements should be
  evident in cognitive reappraisal-related prefrontal cortex
  responses. OBJECTIVE To determine whether CBT for SAD modifies
  cognitive reappraisal-related prefrontal cortex neural signal
  magnitude and timing when implementing cognitive reappraisal with
  negative self-beliefs. DESIGN Randomized clinical trial of CBT
  for SAD vs wait-list control group during a study that enrolled
  patients from 2007 to 2010. SETTING University psychology
  department. PARTICIPANTS Seventy-five patients with
  generalized SAD randomly assigned to CBT or wait list.
  INTERVENTION Sixteen sessions of individual CBT for SAD.
  MAIN OUTCOME MEASURES Negative emotion ratings and functional
  magnetic resonance imaging blood oxygen-level dependent signal when
  reacting to and cognitively reappraising negative self-beliefs
  embedded in autobiographical social anxiety situations. RESULTS During
  reactivity trials, compared with wait list, CBT produced (1) greater
  reduction in negative emotion ratings and (2) greater blood
  oxygen-level dependent signal magnitude in the medial prefrontal
  cortex. During cognitive reappraisal trials, compared with wait list,
  CBT produced (3) greater reduction in negative emotion ratings, (4)
  greater blood oxygen level-dependent signal magnitude in the
  dorsolateral and dorsomedial prefrontal cortex, (5) earlier temporal
  onset of dorsomedial prefrontal cortex activity, and (6) greater
  dorsomedial prefrontal cortex-amygdala inverse functional
  connectivity. CONCLUSIONS AND RELEVANCE Modulation of
  cognitive reappraisal-related brain responses, timing, and functional
  connectivity may be important brain changes that contribute to the
  effectiveness of CBT for social anxiety. This study demonstrates that
  clinically applied neuroscience investigations can elucidate
  neurobiological mechanisms of change in psychiatric conditions.
  TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00380731.

Ment Health Fam Med. 2010 Mar;7(1):49-57.
Feasibility of guided cognitive behaviour therapy (CBT) self-help for childhood anxiety disorders in primary care. Creswell C,
  Hentges F, Parkinson M, Sheffield P, Willetts L, Cooper P.
  Clinical Research Fellow.This study aimed to examine the
  feasibility of guided CBT self-help in primary care for childhood
  anxiety disorders, specifically in terms of therapist adherence,
  patient and therapist satisfaction and clinical gain.Participants were
  children aged between five and 12 years referred to two primary child
  and adolescent mental health services (PCAMHSs) in Oxfordshire, UK,
  who met diagnostic criteria for a primary anxiety disorder. Of the 52
  eligible children, 41 anxious children were assessed for anxiety
  severity and interference before and after receiving CBT self-help
  delivered via a parent (total therapy time = five hours) by primary
  mental health workers (PMHWs). Therapy sessions were rated for
  treatment adherence and parents and PMHWs completed satisfaction
  questionnaires after treatment completion. Over 80% of therapy
  sessions were rated at a high level of treatment adherence. Parents
  and PMHWs reported high satisfaction with the treatment. Sixty-one
  percent of the children assessed no longer met the criteria for their
  primary anxiety disorder diagnosis following treatment, and 76% were
  rated as 'much'/'very much' improved on the Clinical Global
  Impression-Improvement (CGI-I) scale.  There were significant
  reductions on parent and child report measures of anxiety symptoms,
  interference and depression. Preliminary exploration indicated that
  parental anxiety was associated with child treatment outcome. The
  findings suggest that guided CBT self-help represents a promising
  treatment for childhood anxiety in primary care.

Wish I had full text for this one which is specifically for "personality disorders."  Heh, looks like it's published next month.  These are so fresh.

Psychol Psychother. 2013 Sep;86(3):262-79. doi:
  10.1111/j.2044-8341.2011.02060.x. Epub 2012 Feb 20. Three-week inpatient Cognitive Evolutionary Therapy (CET) for patients with
  personality disorders: Evidence of effectiveness in symptoms reduction
  and improved treatment adherence. Prunetti E, Bosio V, Bateni
  M, Liotti G.  Casa di Cura Villa Margherita, Vicenza, Italy
  Scuola di Psicologia Cognitiva S.r.l., Rome, Italy Associazione
  Psicologia Cognitiva, Rome, Italy. Abstract
  Objectives. The aim of this study was to evaluate the efficacy of
  Cognitive Evolutionary Therapy (CET) in an intensive short residential
  treatment of a wide range of severe personality disorders (PDs) that
  resulted in a reduction of social functioning and significant personal
  distress. Design. Each patient was assessed at admission,
  discharge, and 3 months later in order to determine if there was a
  reduction in symptoms and an improved adherence to former outpatient
  programs and to check if patients were undergoing new treatment after
  discharge. Method. Fifty-one patients participated in this
  study. The 20-hr weekly program consisted of two individual sessions
  and various group modules. Outcome measures included: self-reported
  measures of depression, anxiety, general symptoms, number and duration
  of inpatient admissions after the programme, and continuation in an
  outpatient treatment programme. Results. The results show an
  overall improvement in general psychopathology after the release and
  in follow-up sessions, a decrease in the number of further hospital
  admissions, and an increased level of attendance of outpatient
  therapy. Conclusions. This study shows that intensive short
  residential treatment is an effective treatment for patients with a
  wide range of PDs. © 2012 The British Psychological Society.
  J Med Internet Res. 2013 Aug 5;15(8):e153. doi: 10.2196/jmir.2714.

I couldn't fit anymore text into this post.  If you'd like I can make another answer post with more citations though.  I had to trunicate this last one.

The Clinical Effectiveness of Web-Based Cognitive Behavioral Therapy With Face-to-Face Therapist Support for Depressed Primary Care
  Patients: Randomized Controlled Trial. Høifødt RS, Lillevoll
  KR, Griffiths KM, Wilsgaard T, Eisemann M, Waterloo K, Kolstrup N.
   Department of Psychology, Faculty of Health Sciences,
  University of Tromsø, Tromsø, Norway.
  ragnhild.s.hoifodt@uit.no. Abstract
CONCLUSIONS:
  The intervention combining MoodGYM and brief therapist support can be an effective treatment of depression in a sample of primary care
  patients. The intervention alleviates depressive symptoms and has a
  significant positive effect on anxiety symptoms and satisfaction with
  life. Moderate rates of nonadherence and predominately positive
  evaluations of the treatment also indicate the acceptability of the
  intervention. The intervention could potentially be used in a
  stepped-care approach, but remains to be tested in regular primary
  health care.


text:
What is the neurological mechanism behind the "fear of failure"?
Sometimes, the fear of failing at something can be debilitating, and more often than not present a barrier for that person to even try new things - the locus of the fear can be quite different between people - ranging from academic, sporting and relationships and a whole lot more.
So, my question is, what is the neurological mechanism that results in the fear of failure?

Take a look at psychology of risk aversion: https://en.wikipedia.org/wiki/Risk_aversion_%28psychology%29

According neurological perspective,  Amygdala  is involved in pleasurable emotional learning as well as fearful emotional learning. awareness of the aversive nature of  stimuli is sufficient to guide our actions. We avoid dangerous neighborhoods
or shark-infested waters, not mainly because we have been
 attacked by sharks in those locations, but instead
because we might have been given information regarding the stimulus aversive characteristics.
Previous research did substantiate on basis of humans using fear conditioning. they had had found that the amygdala is not completely important in terms learning or developing of an external, cognitive representation of the aversive characters of a stimulus or event .
This cognitive representation that depends on the hippocampal memory
system, which is significant in terms of developing declarative memories, which leads to recalling of past failed experience from hippocampus and feeling sense of fear of failure in future outcomes .although, the amygdala is important for expressing conditioned fear response towards the  same stimuli.
refrence : Phelps, E., O'Connor, K., Gatenby, J., Gore, J., Grillon, C., & Davis, M. (2001). Activation of the left amygdala to a cognitive representation of fear. Nature Neuroscience, 4(4), 437-441. doi: 10.1038/86110


text:
What are the psychological mechanisms behind arrogance?
According to this Wiktionary defintion, arrogance is

1.The act or habit of arrogating, or making undue claims in an overbearing manner; that species of pride which consists in exorbitant claims of rank, dignity, estimation, or power, or which exalts the worth or importance of the person to an undue degree; proud contempt of others; lordliness; haughtiness; self-assumption; presumption.

It is often something that many others in the vicinity find repulsive, sometimes without the person realising it, but, more often than not, they do realise it.
What are the psychological mechanisms that lead to arrogant thoughts, words and actions?

Arrogance is overestimation of one's self worth coupled with the tendency to look at those 'less gifted' as inferior arrogance involves a blatant disegard for people's feelings it is akin to narcissism

Clinically, arrogance is often associated with narcissistic personality disorder.

Narcissistic personality disorder is one of a group of conditions called dramatic personality disorders. People with these disorders have intense, unstable emotions, and a distorted self-image. Narcissistic personality disorder is further characterized by an abnormal love of self, an exaggerated sense of superiority and importance, and a preoccupation with success and power. However, these attitudes and behaviors do not reflect true self-confidence. Instead, the attitudes conceal a deep sense of insecurity and a fragile self-esteem. People with this personality disorder also tend to set unrealistic goals.

DSM-IV-TR diagnostic criteria include (reprinted here):

Criteria for narcissistic personality disorder to be diagnosed include:

Having an exaggerated sense of self-importance
Being preoccupied with fantasies about success, power or beauty
Believing that you are special and can associate only with equally special people
Requiring constant admiration
Having a sense of entitlement
Taking advantage of others
Having an inability to recognize needs and feelings of others
Being envious of others
Behaving in an arrogant or haughty manner

From a scientific standpoint, these characteristics can be difficult to pin down, and clinically, NPD is an "Axis II" diagnosis, which means that most insurance (in the United States) won't cover treatment of the disorder in and of itself.
Consequently, the push to discovering its underlying mechanisms may be less strong, but from theory, they are largely believed to be based on environment.
Proponents of the diagnosis are attempting to adjust the diagnostic criteria a bit to make it more objective for the upcoming DSM-V release.


text:
What are the neurological differences between those who have a high tolerance to pain and those who do not?
I am curious to learn what are the neurological differences between those that have a high tolerance to pain than to those that do not.  Specifically, by high tolerance to pain, I am referring to those people who can just 'work through' any moderate and even severe injury (e.g. a broken arm - as I have seen a couple of people do).

It would be very interesting to see if there are any strategic differences in high-tolerance vs low-tolerance individuals--are high-tolerance individuals using more cognitive management strategies, or is it primarily a physiological difference that determines the difference in pain tolerance?

Much of the "higher order" sensation of pain is processed in the anterior cingulate cortex.

From Wikimedia Commons
There is a movement towards performing anterior cingulotomies in patients with intractable pain.  These procedures are also used to help patients with severe depression or obsessive compulsive disorder, so we have some idea that this area of the brain is a point at which emotional salience is associated with our experience of the world around us.  In the case of pain, post-surgical patients still experience all of the "lower level" symptoms (prostaglandin synthesis, etc.), but do not attach any meaning to them.
So, it is likely that individual differences in this anatomical region could partially account for those who can "work through" the pain versus those for whom it becomes overwhelming.  It's certainly possible that those who can tolerate pain have a lower sensitivity to prostaglandins in their spinal circuitry, but I can't speak to whether that's a valid explanation.

Yen CP, Kuan CY, Sheehan J, Kung SS, Wang CC, Liu CK, Kwan AL (2009) Impact of bilateral anterior cingulotomy on neurocognitive function in patients with intractable pain. J Clin Neurosci., 16(2), 214-9.

Worth noting that acetaminophen (A.K.A. Tylenol) buffers the pain of social rejection too through action on the anterior cingulate cortex!

@NickStauner Very interesting, thanks for pointing that out!


text:
Why do people talk fast in presentations when nervous?
I was at a professional development seminar today, and the presenter, while being interesting and knowing his subject admitted to being nervous and was speaking very fast.  I know I do this when I am giving presentations, despite knowing my audience and my subject.
Why is it that a lot of people will speak faster when nervous?

Are you looking for answer on biological or cognitive level?

@user1406647 I am interested in the cognitive level.

I am experienced presenter, my job is to show presentation, organize educations and trainings to different people, with different personality traits in different situation. Until now I collected more the 700 hours of presentation and more then 120 hours of presentation education. In the beginning I had also that problem, but I overcome it by exercise. Now I am completely relaxed when present.
In my opinion cause of this is social anxiety in self presentation:
Here is one research, but I am sure you can find several more if you look to literature section.
Social anxiety, self-presentation, and the self-serving bias in causal attribution [1980].
Also people get aroused because if they think that other judge them, especially if they do not present a lot... here is model how people conclude others judge them
Mood and judgement: The affect infusion model (AIM) [1995]
EDIT: In this case 'fast talking' is indicator of public speaking fear, so you cant using 'public speaking fear' as cause of 'fast talking' because it will be circular definition. Here is a try to explain this in S-O-R paradigm:
State anxiety patterns for public speaking and the behavior inhibition system [2009]
I don't know exactly what is happening in brain but I assume that something is happening in giri of the hippocampus (working memory) which is overloaded with information of judging environment and accommodate presentation, but also have significant role in speech production.

This explains well that people get nervous when presenting. But why does this nervousness cause presenters to talk faster?

i tried to improve answer

This is an interesting answer, and I agree that evaluation apprehension plays a role, but it still doesn't answer the basic question: why would evaluation apprehension cause fast talking?  Why wouldn't it, for example, cause people to slow down way too much to make sure they get everything right?

@Krysta Maybe it is two-process model. Task oriented presenters will finish their presentation fast, and people oriented presenters will allocate more working memory on participant reactions. It will be very interesting to check this model experimentally.

When speaker lacks confidence about the full-scope of what they present, they stuff in as much as can be spoken to ensure they've covered any 'possible loose ends'.
Lack-of-Confidence ensures the speaker will never have enough, and will jam in more.
A confident speaker understands the core of their topic.  They can speak it in 1 sentence (or 5).  Thus, all other speech is elaboration, not foundation.

I suppose an experiment to test this hypothesis would be to take unconfident people and confident people, induce arousal (inject adrenaline), then see how much more quickly they perform the task about which they are confident.

Why would adrenaline make a difference here?  Just to distract them from potential calm that could allow more-rational thinking

People with low self-esteem yet are unaroused are not commonly known to speak faster than normal. The asker used the term "nervous" which I had interpreted to mean aroused. Double-checking, "nervous" is not synonymous with unconfident, though they can be closely related.

It has been disproven that an aroused brain "thinks faster", but an aroused brain perceives time as passing slower. Thus, an aroused speaker would be inclined to believe that they're speaking too slowly and thus speak faster to compensate.
Even outside of oral presentation, I find this tendency to act faster to be evident when I am playing a first-person shooter video-game and my view (and to a more unfortunate extent, my aim) whips about when I'm having an adrenaline rush, and how a scared animal will act similarly.

This line of thought seems quite reasonable and in my opinion does more towards answering the question than the currently accepted answer. It could further be improved by linking directly to the specific publications you are referring to, potentially seeing whether their findings can be placed more in context or not.


text:
What is the cognitive basis for a sudden loss of confidence in social/professional interactions?
This question is similar to this earlier question, but from a very different viewpoint - what I am asking here is, what is the cognitive basis for a sudden loss of confidence?
For example, if a person has been confidently answering questions in a room of experts, a party or on an online forum (or a Q&A site like here), and encounters negative feedback for what ever reason (and what ever the motive), why is it that some will simply withdraw and become silent?
To put the experience in perspective (note: this is not a request for personal help), when I experience it, it is like the confidence goes out like a light, and only rarely does the 'light' come back on.

I would delete the part about "simply withdrawing and becoming silent" from the question, because there are many other reasons for that behavior that have nothing to do with a loss of confidence. E.g. someone might withdraw because he thinks the other discussants lack the proper understanding, which would be exactly the opposite of lacking confidence.

I believe that it is not confidence that is lacking or undermined. I can know that my answer is correct, and nevertheless feel insecure in the face of an attack. So I am confident of myself, but lack the emotional stability to withstand (unsubstantiated) critique. What is behind the described behavior, in my opinion, is not a lack of confidence, but a lack of self-worth. I rely on constant (!) positive feedback, so I drop into an abyss of self-doubt once it is withdrawn. Healthy individuals can tolerate short periods of social adversity, because they are convinced of their own inherent worth.

Interesting question, and it appears to me that it may be expanded not to just confidence, but other sudden changes in subjective experience as well.

@what: perhaps you can formulate an answer relative to self worth, I thin that would be helpful...

@GregMcNulty I don't have time to hunt for references now. If you want, you can find them and post the answer, I wouldn't mind.