Binary-choice decision time depends upon cerebral hemisphere and nature of task

Binary-choice paradigms are classificatory problems of basic importance to the understanding of elementary decision processes. Generally when subjects decide if two visual stimuli are identical or differ by as little as one element, the decision of "Different" takes longer. This finding is unexpected as decisions of "Different" should not require an exhaustive matching of elements. Using stimulus presentation to the right and left cerebral hemispheres, the right hemisphere initiated fast selections of "Same" for figural material and alone was responsible for the "Same"/"Different" response differential. Exp. 1 (n = 22) gave no differences for same-different, unilateral-bilateral stimulation, and left-right hemispheres. Exp. 2, using word meaning as the binary-choice task, also showed faster decisions for "Same" but a different left-hemisphere-dependent strategy. The nature of information processing in relation to binary-choice tasks is discussed and the utility of bihemispheric paradigms is demonstrated.