Abstract
"Gratton effect (conflict adaptation effect)" refers to the increase of compatibility effects observed in stimulus-response paradigm when the congruent trials appear more frequently, compared to less frequently. We aimed to examine the effects of visual hemifield where task-relevant letter strings are presented on Gratton effect. In Experiment 1, we manipulated the appearance probability for the congruent / incongruent trials (75 % / 25 %) in the left and right visual field. The results showed that the compatibility effect was greater in the hemifield where the congruent trials appear more frequently (75 %), than the hemifield where those appear less frequently (25 %). That is, we found "Gratton effect across hemifields" (left and right). In Experiment 2, we manipulated the appearance probability for congruent / incongruent trials in the upper and lower visual fields, instead of the left and right visual fields. The results obtained in Experiment 2 were different from those in Experiment1. The compatibility effects were not modulated by the appearance probability for the congruent / incongruent trials in the upper-lower visual field. These results obtained in the two experiments suggested that cognitive control in visual processing works independently in the left and right visual hemifield, not in the upper and lower visual hemifield. This finding provides the possibility, that the independent control of visual processing in the left and right visual field may due to that each cerebral hemisphere controls visual attention independently.
