Visual and verbal coding in the interhemispheric transfer of information

A manual response was used to record a decision of ‘same’ or ‘differ’ on two visual signals which were presented simultaneously, either both to the same hemisphere or each to different hemispheres. The signals were drawn from the set of letters A, B, a, b. Eight subjects were required to match on the basis of the names of the letters (irrespective of whether they were capitals or lower case) and eight subjects were required to match on the basis of the visual identity of the signals.Reaction times were measured for ‘same’ and ‘differ’ decisions.This experiment extends a previous study by the same authors (Davis and Schmit 1971). The previous finding, that when two signals are presented each to different hemispheres, reaction times are shorter than when both are presented to the same hemisphere, was confirmed for both visual and name matching. New evidence is provided on the role of each hemisphere in the analysis and comparison of signals, on either a visual or a verbal basis, for ‘same’ and ‘differ’ decisions. A model to explain the results in terms of the different functions of the two hemispheres is proposed.