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Peter Kohler, Anthony Norcia; Identifying cortical areas involved in perceptual decisions about symmetry. Journal of Vision 2016;16(12):129. doi: 10.1167/16.12.129.
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© 2017 Association for Research in Vision and Ophthalmology.
Wallpaper groups are a class of maximally regular textures that consist of 17 sub-groups, each defined by a unique combination of four fundamental symmetries: mirror reflection, translation, rotation and glide reflection (Liu et al 2010). We have previously shown that four of these groups, all containing rotation symmetry, elicit responses in human visual cortex that increase linearly with the maximal order of rotation symmetry present in each group. We observed this effect in three areas of the ventral visual processing stream (V4, VO1 and LOC), as well as in area V3, but not in earlier visual areas (Kohler et al., J. Neurosci., in press). These results raise an important question: Which parts of this network of areas drive behavioral responses about symmetry? Here we address this question using a perceptual decision-making task and EEG source imaging of response-locked activity. Participants discriminated images containing rotation symmetry from control images containing only translation symmetry in a speeded two-alternative forced choice task. We localized EEG responses evoked during the task to functionally defined regions-of-interest in visual cortex. We found responses that differed for fast and slow reaction times in visual areas including LOC, V4, and potentially V3. V1 showed no evidence of this effect. This indicates that the timing of behavioral responses to symmetry in wallpaper groups is driven by activity in visual areas at least as early as V4. There is converging evidence that perceptual decision-making is at least partly driven by areas that are also associated with the encoding of input stimuli (Ales et al 2013, Cottereau et al 2014, Dmochowski & Norcia 2015). Our data are well aligned with these findings, and emphasize the contribution of early visual areas to multiple visual tasks, including the detection of visual symmetry.
Meeting abstract presented at VSS 2016
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