Apparent movement in relation to homonymous and heteronymous stimulation of the cerebral hemispheres.

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Abstract
The purpose was to deter-mine whether interaction between excitations in the same cerebral hemisphere is greater than interaction between excitations in different hemispheres. The phenomenon of apparent movement was used as anindicator of interaction. Four black dots on a white background, arranged as the corners of a 5 mm. square were used as stimulus objects. The field was viewed monocularly; distance of the dots from the subject''s eye was 13 inches. The 2 dots forming one diagonal of the "square" were presented together, extinguished, and then followed 0.1 sec. later by the 2 forming the other diagonal. In this way, the stimulus conditions could give rise either to apparent vertical or apparent horizontal movement. Whether the one or the other took place could not be dependent on the conditions of peripheral stimulation, but on cerebral factors alone. Control of the cerebral factors was secured by varying the position of the fixation point relative to the 4 dots. It was found that when the fixation point was in the center of the "square," the subjects saw predominantly vertical movement, that is, movement between the 2 dots constituting each of the 2 vertical "sides" of the "square." In this case the fixation point fell on the retinal mid-line and the 2 dots forming a given vertical side fell on the same hemisphere. When the fixation point was to one side of the "square," it was found that there was no predominance of one type of apparent movement over the other. In this case the excitations from the 4 dots all fell on the same hemisphere. It was concluded that there is greater interaction between cerebral excitations in the same hemisphere than between cerebral excitations in disparate hemispheres.

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