Global shape aftereffects have a local substrate: A tilt aftereffect field

Abstract

Adaptation to prevailing stimuli is a ubiquitous property of the visual system that optimizes its dynamic range. The perceived difference in orientation of successively presented lines of similar orientation is exaggerated and the perceived shape of an object is influenced by previously experienced shapes. Change in perceived shape is assumed to arise through the adaptation of shape detectors. Here we consider an alternative: adaptation within a substrate of local oriented line detectors resulting in enhanced shape contrast in similar shapes. We show that the perceived shapes of a spatially coincident circle and Cartesian grid can be manipulated independently by adaptation to geometrically transformed copies of themselves. The same transformation was applied to the circle and the grid to create the adaptors; therefore, the specificity of the effects of adaptation demonstrates that the visual system adapts to the shape of objects rather than applying transformations to the reference frame of the visual field. The tilt aftereffect predicts local changes in perceived orientation, and fields of such local effects can often account for the global change in perceived shape of complex objects, including faces.

Norms are Not the Norm: Testing Theories of Sensory Encoding Using Visual Aftereffects

“…The locally-repulsive pattern of aftereffects we observe is consistent with a model in which face aftereffects arise from local interactions, such as those that govern the tilt aftereffect (Dickinson et al, 2010;Dickinson & Badcock, 2013;Dickinson et al, 2012). However, as yet it is unclear how this model can account for the transfer of aftereffects between differentlysized adapting and test stimuli.…”

“…In most circumstances perceptual aftereffects, even those for supposedly complex stimuli (such as shapes and faces), will at least partially reflect the effects of adaptation to low-level image properties (Dennett et al, 2012;Dickinson et al, 2010;Xu, Dayan, Lipkin, & Qian, 2008). We minimized such contributions by using dynamic, texture-defined white noise as an adaptor.…”

“…Adaptation to a globally distorted image can be thought of as adaptation to a systematically biased orientation field (Dickinson et al, 2010(Dickinson et al, , 2012. If the adaptor and test were presented at the same size and retinal location, one would expect this field of tilt aftereffects to manifest as a local repulsion along the facial-distortion dimension (Webster & MacLeod, 2011).…”

“…A fundamental question regarding such aftereffects is whether they arise from adaptation within substrates explicitly encoding complex attributes, or whether they can be explained entirely by the aggregation of aftereffects between simpler image elements such as colour, contrast, and edge orientation (see, e.g. Dickinson, Almeida, Bell, and Badcock (2010) and Dickinson and Badcock (2013)). …”

“…As adaptation to spatial patterns likely occurs at multiple levels of visual processing (Dhruv & Carandini, 2014;Dickinson et al, 2010Dickinson et al, , 2012Xu et al, 2008), and we wanted to investigate shape-specific adaptation, it was important to mitigate, as far as possible, the effects of adaptation in mechanisms encoding local contrast or orientation. For example, when adapting and test shapes overlap, any observed effect could be strongly impacted by contour repulsion or tilt aftereffects, likely produced in primary visual cortex rather than later shape-specific stages of processing (Dragoi et al, 2000;Jin et al, 2005).…”