Interhemispheric interaction in bilateral redundancy gain: effects of stimulus format.

Previous visual laterality experiments have shown that identification is better when 2 copies of the same stimulus are presented--1 to each hemisphere--than when only a single copy is presented to 1 hemisphere. New experiments were conducted to vary whether the 2 stimuli on a bilaterally redundant trial were physically identical or identical in format in addition to leading to identical responses. Substantial bihemispheric gain was obtained even when the 2 stimuli were perceptually distinctive (e.g., letter trigrams differing in case and font or the same numeric quantity represented by digits and dots). Thus, much of the bihemispheric advantage involves relatively abstract aspects of information processing. However, when the formats were sufficiently distinctive, there were small effects on bihemispheric performance, suggesting some role for less abstract processes that are sensitive to physical characteristics.