Interhemispheric interaction in semantic categorization of pictures.

Interhemispheric processing may either increase or decrease the processing power of the brain. The two experiments presented here examined in normal subjects whether hemispheric interaction would be useful or not in semantic categorization of pictures. It was tested whether the advantages of dividing the processing between the hemispheres would increase when the experimental task was kept constant but the computational demands of the stimuli was increased. The critical stimuli were either identical (two copies of the same picture) or semantically related pictures (e.g., apple-banana). The stimuli were presented either unilaterally to the same hemisphere or bilaterally to the opposite hemispheres. The results from the two experiments showed a bilateral advantage in categorization of the semantically related pictures but not in categorization of the less demanding identical pictures. The results support the hypothesis that the cognitive capacity of the brain can be increased by dividing the processing of relatively demanding stimuli between the hemispheres.