| Hemispheric interaction in two types of face processing tasks was examined using a divided visual field paradigm. In the first set of experiments, a face comparison task with bilateral presentation was used to look at the ability of the hemispheres to collaborate in face processing. In the second set, an attended facedness decision task with a distractor in the opposite visual field was used to look at the ability of the hemispheres to function independently in face processing. Performance with unilateral and central vision presentation was also investigated for comparison purposes.; For the face comparison task, performance was examined for both simultaneous and sequential presentation. The bilateral distribution advantage for simultaneous presentation, typically seen as evidence for collaboration, was not found. Instead the simultaneous task revealed a bias to respond "same" with bilateral presentation and "different" with unilateral presentation. For the sequential task, there was no evidence of bias but rather an overall LVF advantage for both accuracy and latency with performance for bilateral presentation corresponding to that for unilateral presentation in the visual field which viewed the second face. Performance in central vision yielded a pattern very similar to that observed when the faces were presented lateralized to the LVF. The "same" bias for simultaneous bilateral comparisons was taken as evidence of a loss of detail when such comparisons are made across hemispheres. The lack of bias for sequential presentations was taken as evidence that a more abstract code may be used for such comparisons which is less subject to degradation.; For the attended face detection task, the visual field effects were interpreted as evidence for callosal relay with non-face decisions being made in the RH. Only non-face targets showed significant evidence of interference from distractors and then, only when the target preceded the distractor either as a result of interhemispheric transfer time or vertical location. This finding was taken as evidence that non-face decisions require additional resources which, if occupied processing a distractor, reduce the accuracy of detection of a subsequent non-face target. The effect was also demonstrated to extend across trials. |
