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The Effects of Handedness and Bilateral Saccadic Eye Movements on False Alarms in Recognition Memory

Handedness can be used as a marker for interhemispheric interaction, which can produce memory benefits. Bilateral saccadic eye movements can be used to manipulate levels of interhemispheric interaction. This study measured the effects of handedness and bilateral saccadic eye movement on memory using the Deese-Roediger-McDermott paradigm. This study predicted a memory advantage for left-handers and mixed-handers without eye movements and an advantage for right-handers with the eye movements. The results do not support these predictions but do suggest that handedness is a factor in episodic memory performance. The analyses for this study were run using A’ to compare false alarm rates for critical lures and for unrelated new items. Mixed-handers were less susceptible to the DRM paradigm, as the made fewer critical false alarms than both left-handers and right-handers. The bilateral saccadic eye movements increased the number of critical false alarms for left-handers but did not affect righthanders or mixed-handers. Reaction times data indicated that participants treated critical lures like old items. Running head: EFFECTS OF HANDEDNESS ON MEMORY 3 The Effects of Handedness and Bilateral Saccadic Eye Movements on False Alarms in Recognition Memory People tend to think of handedness is only related to common tasks like writing or throwing a ball, but hand dominance and its relationship with neural functioning have more far reaching consequences. Handedness can be defined as the general preference of one hand over the other for basic motor functions, and can vary in both strength and direction (Oldfield, 1971). In addition, the term handedness can apply to lateral preferences for tasks that do not involve the hands, such as kicking a ball and monocular vision. Handedness is somehow reflected in the brain, but there is no handedness area that we are aware of. We do know that handedness can affect the brain and mental processes in large part due to research on dyslexia, which is more common in left-handers than in right-handers (Geschwind, 1983). In addition, left-handers are more likely to have language lateralized in the right hemisphere or bilaterally organized than right-handers (Knecht et al., 2000). However, researchers as well as people in general do not fully understand the implications of handedness for cognitive processes, such as memory. The current study will examine the effects of handedness on episodic memory performance. Interhemispheric Interaction Interhemispheric interaction is the degree to which the left and right hemispheres of the brain communicate with each other via the corpus callosum (Witelson, 1985). The corpus callosum connects the two hemisphere of the brain and is responsible for the majority of interhemispheric interaction. Handedness is linked with the degree of interhemispheric interaction. The general pattern is that right-handers exhibit less interhemispheric interaction than mixed-handers and left-handers (Christman & Propper, 2001; Christman, Propper, & Brown, 2006; Christman, Propper, & Dion, 2004; Lyle, McCabe, & Roediger, 2008; Propper & Running head: EFFECTS OF HANDEDNESS ON MEMORY 4 Christman, 2004; Propper, Christman, & Phaneuf, 2005; Witelson, 1985). There is evidence to suggest that the disparity in the degree of interhemispheric interaction found in left-handers and right-handers is due to differences in the size of the corpus callosum, with left-handed and ambidextrous individuals possessing larger corpus callosa than right-handed individuals (Witelson, 1985). There are clear anatomical asymmetries associated with handedness, since the corpus callosum is larger in non-right-handed individuals than in right-handed individuals (Witelson, 1985). Many researchers use the term non-right-handers instead of left-handers, because it is difficult to find sufficient numbers of left-handed participants, and non-right-handers include mixed-handers. There are more specific variations in corpus callosum size that also take hemispheric laterality into account. Language lateralization in the right hemisphere is correlated with a larger corpus callosum. Individuals whose language capacities are lateralized to the left or bilaterally represented have smaller corpus callosa than individuals with right hemisphere language lateralization (Cowell, Kertesz, & Denenber, 1993). There is evidence for sex differences interacting with handedness to affect the size of the corpus callosum (Habib et al., 1991). Possibly because of the influence of hormonal differences, non-right-handed males have larger corpus callosa than right-handed males, but non-right-handed females have smaller corpus callosa compared to right-handed females (Habib et al., 1991). Because of the evidence connecting non-right-handedness to increased levels of interhemispheric interaction, measure of handedness can be used to gage levels of interhemispheric interaction without any direct neurological measures. The benefits of nonright-handedness on episodic memory ability have been attributed to increases in interhemispheric interaction. Mixed-handed individuals exhibit superior recall of both lab-based Running head: EFFECTS OF HANDEDNESS ON MEMORY 5 and autobiographical episodic memories in comparison to strongly right-handed individuals (Propper et al., 2005). This result places the advantage of non-right-handedness with the mixedhanded group, but it remains unclear which non-right-handers have greater baseline levels of interhemispheric interaction and experience episodic memory benefits because of it. The next section reviews the observed relationship between handedness and episodic memory abilities.