Phase specific shape aftereffects explained by the tilt aftereffect.

Abstract

Aftereffects of adaptation are frequently used to infer mechanisms of human visual perception. Commonly, the properties of stimuli are repelled from properties of the adaptor. For example, in the tilt aftereffect a line is repelled in orientation from a previously experienced line. Perceived orientation is predicted by the centroid of the responses of a population of mechanisms individually tuned to limited ranges of orientation but collectively sensitive to the whole possible range. Aftereffects are also predictable if the mechanisms are allowed to adapt. Adaptation across radial frequency patterns, patterns deformed from circular by a sinusoidal modulation of radius, causes repulsive aftereffects, sensitive to the relative amplitudes and orientations of the patterns. Here we show that these shape aftereffects can be accounted for by the application of local tilt aftereffects around the shape contour. We suggest that fields of tilt aftereffects might provide a general mechanism for exaggerating the perceptual difference between successively experienced stimuli, making them more discriminable. If the human visual system does indeed exploit this possibility, then the conclusions often made by studies assuming adaptation within mechanisms sensitive to the shape of stimuli will need to be reconsidered.

The statistics of natural shapes predict high-level aftereffects in human vision

“…Many previous studies showed a rough correspondence between psychophysically-measured bandwidths for basic visual properties (e.g., spatial frequency, orientation, and colour) and those in single neurons from the early visual cortex known for coding local information (Lennie and Movshon, 2005). The correspondence has long fueled the debate as to whether shape aftereffects are due to local or global processes (Suzuki, 2005;Storrs, 2015;Bowden et al, 2019).…”

“…One well-known method for examining shape coding is with adaptation paradigms that produce shape aftereffects. In such experiments, prolonged viewing of one shape (‘adaptor’) makes a subsequently presented shape (‘test’) appear distorted (Regan and Hamstra, 1992; Rivest, Kim, and Sharpe, 2004; Suzuki and Cavanagh, 1998; Suzuki, 2001, 2003, 2005; Fleming, Holtmann-Rice, and Bülthoff, 2011; Storrs and Arnold, 2013, 2017; Bowden et al, 2019). A given test shape can take on multiple different post-adaptation appearances, depending on which shapes are used as adaptors (e.g., Regan and Hamstra, 1992; Suzuki, 2001, 2005; Storrs and Arnold, 2017; Bowden et al, 2019).…”

“…we directly pit an empirically-derived high-level statistical shape space against a number of local, low-level aftereffect models that are inspired by both neurophysiology (i.e., early stages of visual processing) and previous psychophysical work (e.g., TAE; Bowden et al, 2019).…”

Analysis of shape uses local apparent position rather than physical position

“…Increased sensitivity of neuronal receptive fields centered on a projected path might cause stimuli adjacent to the path to be perceived as nearer the path than they actually are, lending the path some perceptual stiffness and making position somewhat subordinate to continuity of the path. Previously we have used Euler's method to predict the perceived shapes of paths subject to local contextual illusions ( Bowden et al, 2019 ; Dickinson, Almeida, et al, 2010 ; Dickinson, Harman, et al, 2012 ). Obviously, the visual system would not use a serial system of determining the form of a path but it is conceivable that excitatory connections between neurons signaling illusory orientations will result in the perceived position of the path being displaced, due to the enhancement in sensitivity of receptive fields that are not centered on the physical path, if the local position is encoded in the responses of a population of neurons.…”

“…The perceived shape of an object is, however, also influenced by contextual effects that act more locally. Local effects of orientation context, for example, have been shown to influence perceived shape ( Bowden, Dickinson, Green, & Badcock, 2019 ; Dickinson, Almeida, Bell, & Badcock, 2010 ; Dickinson & Badcock, 2013 ; Dickinson, Mighall, Almeida, Bell, & Badcock, 2012 ). Under certain conditions, local contextual effects can also lead to the misinterpretation of the configuration of a path.…”