CEREBRAL HEMISPHERIC ASYMMETRY: BASIS OF DUAL COGNITIVE SYSTEMS? (CEREBRAL DOMINANCE)

The research on functional bilateral asymmetry and its possible evolutionary basis were selectively reviewed. It was proposed that the two cerebral hemispheres are the loci of two different cognitive systems. The left hemisphere interprets sensory information and orchestrates motor output in accordance with linguistic rules, the right hemisphere in accordance with rules for carrying out operations in three-dimensional space. The cognitive programs which carry out interpretive functions are common to the two systems, while those responsible for the generation of activity are radically different and logically incompatible. Other research tending to indicate distinct cognitive systems (specifically, research on impression formation and the mere exposure effect) was reviewed, and it was proposed that these cognitive systems are located in opposite cerebral hemispheres. Two experiments using a dichotic listening task were conducted to look for laterality effects in impression formation. The valence and emotionality of words presented to the two ears were varied, so that the relative contributions of words heard in the left and right ears could be compared. It was expected that the words heard in the left ear would be more influential, since it was hypothesized that the impression formation task evokes relatively more right hemisphere processing than does simple verbal recall. In the second experiment; the same stimuli were used for a free recall task. The results overall did not support the hypothesis. The impression formation data did not show a left ear bias; in fact, the result (although not significant) tended to show a greater right ear contribution. The recall data showed higher recall of words heard in the right ear. A significant interaction revealed that words heard in the right ear were equally likely to be recalled whether positive or negative; however, negative words presented to the left ear were more likely to be recalled than positive words presented to the same ear. Finally, reasons for the negative findings and alternative methodologies were discussed