Testing hemifield independence for divided attention in visual object tasks.

In this study, we asked to what degree hemifields contribute to divided attention effects observed in tasks with object-based judgments. If object recognition processes in the two hemifields were fully independent, then placing stimuli in separate hemifields would eliminate divided attention effects; in the alternative extreme, if object recognition processes in the two hemifields were fully integrated, then placing stimuli in separate hemifields would not modulate divided attention effects. Using a dual-task paradigm, we compared performance in a semantic categorization task for relevant stimuli arranged in the same hemifield to performance for relevant stimuli arranged in separate left and right hemifields. In two experiments, there was a reliable decrease in divided attention effects when stimuli were shown in separate hemifields compared to the same hemifield. However, the effect of divided attention was not eliminated. These results reject both the independent and integrated hypotheses, and instead support a third alternative - that object recognition processes in the two hemifields are partially dependent. More specifically, the magnitude of modulation by hemifields was closer to the prediction of the integrated hypothesis, suggesting that for dual tasks with objects, dependent processing is mostly shared across the visual field.