system
Given the following post, respond as if you're commenting on Reddit:
human
How much is the "lag" in the real world?

When playing multiplayer video games, we often experience lag. I think it can be defined as the length of time since the information is sent from the server until it is received by the computer being played on. The player then experiences the game a few milliseconds after it actually happens.

I was wondering how much lag is there in the real world? How much time does it take, for example, for the eyes to receive information send it to the brain and for the brain to "experience" what's happening?
gpt
We can actually measure how long certain signals take to propagate through the nervous system using a technique called evoked potentials. Using a set of electrodes on the scalp surface, you measure the response of the brain to a long set of stimuli and average them to get rid of all the random, moment-to-moment signals. Then you get a reproducible waveform.

For instance, there's a peak called N20 (sometimes N19) which corresponds to the arrival of sensory information from the wrist to the primary sensory cortex. This takes about 20 milliseconds. Arrival at the primary sensory cortex is just the very first step of sensory processing, but that means a sensory "lag" from your wrist is at least 20 ms long. From the foot it's more like 45 ms.

In the visual system, there are multiple identified responses and no clear agreement about what they mean. The N75 response is thought by some to represent the first arrival of visual signals to the occipital cortex, where visual processing begins. This would give a minimal visual "lag" of 75 ms; however, the P100 wave is associated with actual perception of visual stimuli, meaning the lag might be as much as 100 ms.

There are a lot of evoked potentials that have been described. There's a P300 that, to simplify, represents the recognition of a meaningful (as opposed to arbitrary or meaningless) visual stimulus. That's as much as 500 ms after the stimulus.

The idea of "lag" however is complicated by the fact that there is some sort of processing going on through the entire process. Even before visual signals arrive at the occipital cortex, basic processing in the retinal ganglion cells have started to define color opposition and contrast. That's within the first 10 ms. So the fact that it takes 50 or 75 or 100 ms to make it to the visual part of the brain doesn't make it a lag in the same way a server lag is a lag.