008-23 – Task-independent allocentric representation of symmetry using polygons

Visual symmetry activates regions in the extrastriate cortex and generates an ERP component called the Sustained Posterior Negativity (SPN). The extrastriate symmetry network can overcome visual distortions that destroy regularity in the image and achieve an allocentric representation of symmetry. A previous study has shown that these allocentric representations are only constructed when symmetry is task relevant (Makin et al., 2015). However, it is possible that some stimulus types facilitate allocentric representations during secondary tasks. To test this, we compared SPN responses to symmetrical configurations of Gabors and solid polygons. Stimuli were either presented in the frontoparallel plane or with perspective distortion. There were 3 groups of 40 participants. The first group performed a regularity discrimination task, the second group performed a luminance discrimination task and the third performed a sound-luminance congruency task. We observed an SPN response for Gabors and solid polygons in all 3 tasks. In all tasks the SPN was larger (i.e., more negative) for the frontoparallel stimuli than perspective stimuli. This perspective cost was reduced by solid polygons, compared to Gabors. We conclude that some level of allocentric representation occurs in all tasks and with different stimuli, however, there is no case where perspective cost is reduced to zero. This suggests that conditions for view invariance are more subtle than suggested by Makin et al. (2015). Future work will examine SPN magnitude in rich scenes with different cues to facilitate automatic allocentric representations.