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Jordan Lass, Ali Hashemi, Patrick Bennett, Mary Peterson, Allison Sekuler; Neural Signals Underlying the Convexity Context Effect. Journal of Vision 2014;14(10):255. doi: 10.1167/14.10.255.
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© ARVO (1962-2015); The Authors (2016-present)
Convexity is relevant to figure assignment, but the relationship is display-dependent: Convex regions are more likely to be perceived as figures in 8- than 2-region displays, provided concave regions are homogeneously colored. This convexity context effect (CCE) may occur because multiple homogeneous concave regions (8-region displays) are more likely than the single concave region (2-region displays) to be interpolated into a surface behind the convex regions, making convex regions stand out as figures in 3D. Without such interpolation, 2-region displays may appear flat. Here we examined the neural signals underlying CCEs using electroencephalography to determine the effect of region number and perceptual interpretation on those signals. On each trial, a small probe appeared on one of two central regions of 2- or 8-region black & white displays. Observers (N=10) indicated whether the region containing the probe was figure or ground. Overall behavioural results were in the direction predicted by the CCE, although there was considerable variability across individuals. Our most consistent result was an effect of region number on the P2 amplitude for the grand average evoked response potentials (ERPs), with greater amplitudes for 8- than 2-region displays (p<0.0001). We found additional, but smaller, effects of region number on P1 and N1 latency: 8-region displays led to earlier peaks than 2-region. At the group level, there were no effects of figure-ground perception up to about 300 ms. Highly variable behavioural CCEs obtained across subjects led us to examine effects of perceptual differences on ERPs. When considering just subjects with strong behavioural CCEs, P1 and N1 components showed an effect of perceptual interpretation in the 8- but not 2-region displays. Overall, our results suggest that the magnitude of CCEs may be correlated with differences in early neural signals, and that the P2 may be linked to the perception of 3-dimensionality.
Meeting abstract presented at VSS 2014
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