ULTRA RAPID FACE DETECTION IN NATURAL IMAGES : IMPLICATIONS FOR COMPUTATION IN THE VISUAL SYSTEM

Using a choice saccade task, Kirchner and Thorpe recently demonstrated that detection of animals in natural scenes is considerably faster than previously supposed [1]. Here we present some new data with the same task that show that face detection is even more efficient. When two images are flashed to the left and right of fixation, subjects can accurately make saccades to the side where there is a human face with a mean reaction of time of only 147 ms and an accuracy level of 94%. The earliest reliable saccades were made as early as 110 ms after stimulus onset. If we allow roughly 20 ms for saccade initiation, such data leaves very little time for visual processing and seems to rule out computations that require more than one spike per neuron. Furthermore, it seems clear that only a feedforward pass through the visual pathways can be performed in so little time.

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