Effects of aging and exposure duration on perceptual biases in chimeric face processing.

Experiments using chimeric faces, where the left and the right hand side of the face are different, have shown that observers tend to bias their responses toward the information on the left. Here we investigate the effects of aging as well as exposure duration on this leftward bias. Forty female and male blended as well as chimeric faces were presented to 24 young and 23 elderly adults in either sub-saccadic 100 msec, 300 msec or free view conditions. We found firstly that an increase in exposure duration resulted in an increase in the degree of leftward perceptual biases, irrespective of age, in line with hypotheses stressing the contribution of scanning to chimeric face processing. Secondly, fundamental differences in the perceptual biases between the groups were found in so far that the younger subjects demonstrated significant perceptual biases to chimeric face stimuli even at sub-saccadic exposure durations, whilst for older adults this was the case for the 300 msec and free view conditions only. This differential perceptual activity can be viewed in terms of either reduced right hemispheric function, or increased bilateral function as a possible consequence of elderly adults experiencing the task as more effortful.