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Sébastien Crouzet, Simon J. Thorpe, Holle Kirchner; Category-dependent variations in visual processing time. Journal of Vision 2007;7(9):922. doi: 10.1167/7.9.922.
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In a choice saccade paradigm where two natural scenes are simultaneously flashed left and right of fixation, subjects can initiate saccades to the side containing an animal in as little as 120 ms (Kirchner & Thorpe, Vis Res, 2006). Here, we investigated whether this processing time depends on the nature of the target category. Previous go/no-go studies had suggested that rapid processing of natural scenes was comparable for categories such as animals, faces and means of transport (VanRullen & Thorpe, Perception, 2001; Rousselet et al., JOV, 2004). But in the present experiments, we found clear evidence that certain image categories were processed more rapidly than others. In different blocks of trials, subjects had to respond to target categories such as animals, faces and means of transport using distractors that were made of various landscapes. The results showed a category-dependent variation of processing time. Mean RTs, varied from 140 ms for human faces (with the first saccades occurring only 110 ms after stimulus onset) to 190 ms for means of transport. In a second series of experiments, we investigated the effect of the type of distractor on performance, testing categories against each other. A major observation was that the image categories that were fastest when used as targets were also the most disturbing ones when they were used as distractors. These category-specific differences in processing time may also be reflected in the fact that certain key stimuli such as faces are also more resistant to backward masking and rapid sequential visual presentation (Bacon-Macé et al., in preparation). We propose that the ability to perform the choice saccade task and the resistance to masking could both reflect the speed with which information can be extracted during cortical processing.
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