Images presented at fixation provide more information to the visual system than images presented parafoveally. However, it is not clear whether it is more beneficial to receive the larger amount of information first in sequential categorical comparisons. Theories based on activation of mental sets, pure information content, or interference make different predictions on the likely outcomes of such tasks. In our study, subjects made same-different category judgments on a large set of briefly appearing pairs of grayscale images of everyday objects, which were presented on a gray background. Each image extended 5 degrees of visual angle, could appear in either the center (C) or corners (S) of the screen for 12.5, 25, or 50 msec, and was followed by a random mask presented for 25 msec. Pairings of position, timing, and category were fully randomized and balanced across trials, and the ISI between the two images within a trial was kept at 12.5msec. Subjects were instructed to fixate at the center of the screen, and their eye movements were monitored. There was a significant advantage in conditions where the central image appeared first and the peripheral image second (C-S) compared to the opposite order (S-C) (t(16)=0.02, p [[lt]] 0.05). However, the relation between stimulus presentation time and categorization performance in the C-S condition was non-monotonic: longer duration was not always paired with better performance. These results rule out pure information-based explanations and suggest that object information received earlier constrains how efficiently information received subsequently is processed in categorization tasks.

Leave a Reply

Your email address will not be published. Required fields are marked *