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Sébastien M. Crouzet, Simon J. Thorpe; Power spectrum cues underlying ultra-fast saccades towards faces. Journal of Vision 2010;10(7):634. doi: https://doi.org/10.1167/10.7.634.
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When images of a face and a vehicle are flashed left and right of fixation, subjects can selectively saccade towards the face only 100 ms after image onset (Crouzet et al., submitted). This is so quick that it probably does not allow time for complete analysis of the image by the ventral stream. What sorts of information could be used for triggering such fast saccades? One possibility is that this ultra-rapid processing relies on relatively low level power spectrum (PS) information in the Fourier domain (Honey et al., J. Vis., 2008). Thus, PS normalization in the task can significantly alter face detection performance, especially for the very first saccades (Crouzet et al., ECVP 2008). However, a decrease of performance following PS normalization does not prove that PS-based information is sufficient to perform the task (Gaspar & Rousselet, Vis. Res., 2009). Following the Gaspar and Rousselet paper, we used a swapping procedure to clarify the role of PS information in fast face detection. Our experiment used 3 conditions: (i) with the original images, (ii) inverted, in which the face image has the PS of a vehicle, and the vehicle has the PS of a face, and (iii) swapped, where the face has the PS of another face, and the vehicle has the PS of another vehicle. The results showed very similar levels of performance in the original and swapped conditions, and a huge drop in the inverted condition. The conclusion is that, in the early temporal window offered by the saccadic choice task, the visual saccadic system effectively makes use of low level PS information for fast face detection, implying that faces may be detected by some particular combination of spatial frequency and orientation energy.
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