Visual attention in split-brain monkeys

Abstract

How the separated hemispheres of a split-brain animal avoid conflict with each other remains uncertain. In some circumstances both hemispheres seem to be able to attend to separate stimuli simultaneously^1,2. Yet, when a split-brain animal has received separate training in each hemisphere on visual discrimination tasks which require opposite solutions, and is then placed in a situation where either hemisphere could respond, conflict does not occur. Instead, one hemisphere dominates behaviour for a variable time, then the other assumes control³. Independent variation of degree of attention in each hemisphere has been hypothesised to account for this⁴. We have sought electroencephalographic evidence of such hemispheric independence of visual attention in the split-brain animal, since a change in the power spectrum of the EEG accompanies increased visual attention—that is, an increase in θ (4–7 Hz) and β (13–25 Hz) frequency power, and a decrease in α (8–12 Hz) frequency power⁵. Power spectrum analysis has given evidence of alternate dominance of visual attention in the separated hemispheres. This finding has implications for the absence of hemispheric conflict in such animals, and the development of hemispheric specialisation in man.