Neural responses to dynamic adaptation reveal the dissociation between the processing of the shape of contours and textures

Abstract

Shape-adaptation studies show that surround textures can inhibit the processing of contours. Using event-related potentials (ERP), we examined the time-course of neural processes involved in contour-shape and texture-shape processing following adaptation to contours and textures. Contours were made of Gabor strings whose orientations were either tangential or orthogonal to the contour path, while textures were made of a series of contours arranged in parallel. We found that in the absence of adaptation, the perceptual N1 component for contour-tests peaked later and increased in amplitude compared to the N1 for texture-tests, consistent with previous literature on contour and texture-driven ERPs. Following adaptation, the ERP difference wave (no-adaptor minus with-adaptor conditions) for contour-tests showed two components: an early (70-230 ms) and a late component (250-500 ms) that were differentially affected by the presence of surround-texture adaptor. From the temporal sequence of ERP modulations, we conclude that texture processing begins before contour processing and encompasses the stages of perceptual processing reflected in the earliest components of the visual evoked potential (P1 and N1). Interestingly, our dynamic adaptation paradigm shows two difference-wave components that are differentially modulated by adaptation to contours when presented in isolation (no-surround) and embedded in texture-surround (context). Altogether these findings support the dissociation between contour and texture processing mechanisms in human vision.