Evaluating shape after-effects with radial frequency patterns

Abstract

Mechanisms selective for complex shape are vulnerable to adaptation techniques historically used to probe those underlying performance in lower-level visual tasks. We explored the nature of these shape after-effects using radial frequency patterns. Adapting to a radial frequency pattern resulted in a strong and systematic after-effect of a pattern that was 180 degrees out of phase with the adapting pattern. This after-effect was characterized as both a shift in the point of subjective equality and an increase in response uncertainty. The after-effect transferred across adapting pattern contrast and adaptor amplitude, suggesting an involvement from shape-specific mechanisms located at higher processing stages along the visual pathway. Moreover, our results suggested that the shift in the point of subjective equality was guided by global processing mechanisms, whereas the increase in uncertainty reflected activity from local processing mechanisms. Together, these results suggest that shape-specific after-effects reflect gain control processes at various stages of processing along the ventral pathway.

Local motion effects on form in radial frequency patterns

“…Wilson (2004, 2005) favored the first of these interpretations citing evidence that motion RF modulation pedestals had a detrimental effect on discrimination thresholds for spatial RF deformation both in phase and out of phase with the test pattern modulation. However, the perceived form of a motion RF pattern has amplitude maxima at the points where the motion is maximally centrifugal and spatial RF patterns have been shown to elicit spatial RF after effects of opposite phase (Anderson et al, 2007) which raises the question of whether motion RF patterns exhibit spatial RF after effects of opposite phase. The spatial RF after effect is independent of the contrast of the adapting stimulus (Anderson et al, 2007) suggesting the neural mechanisms responsible for encoding the shape are downstream of those effecting contrast gain control.…”

“…However, the perceived form of a motion RF pattern has amplitude maxima at the points where the motion is maximally centrifugal and spatial RF patterns have been shown to elicit spatial RF after effects of opposite phase (Anderson et al, 2007) which raises the question of whether motion RF patterns exhibit spatial RF after effects of opposite phase. The spatial RF after effect is independent of the contrast of the adapting stimulus (Anderson et al, 2007) suggesting the neural mechanisms responsible for encoding the shape are downstream of those effecting contrast gain control. Experiment 1 of this study demonstrates that the after effect develops over a very short adaptation period (40 ms) and in the absence of an intervening stimulus the adaptation is persistent in comparison to the rise time.…”

“…The effects of motion on perceived position are local but if speed were modulated sinusoidally around a circle the resulting local displacements would give the impression of spatial form in phase with the speed modulation. Adaptation to spatial RF patterns has been shown to result in a subsequently presented circle appearing to have the opposite phase of modulation (Anderson, Habak, Wilkinson, & Wilson, 2007), therefore motion RF patterns should give rise to opposite phase after effects in low amplitude spatial RF patterns and vise versa. Our hypothesis, that the perception of motion-defined form arises from the integration of positions perceived as displaced in the direction of local motion is supported by a series of five experiments giving the following five results.…”

(In) Sensitivity to spatial distortion in natural scenes

“…Complex-shaped closed figures can be synthesized from the sum of a set of simple radial frequency patterns of differing cyclical period, amplitude and phase. Adaptation (Anderson, Habak, Wilkinson, & Wilson, 2007; Bell, Wilkinson, Wilson, Loffler, & Badcock, 2009), masking (Bell, Badcock, Wilson, & Wilkinson, 2007) and sub-threshold summation (Bell & Badcock, 2009) studies suggest that the perception of spatial structure in these patterns is based on the outputs of a set of channels, each of which is selective for a narrow range of radial modulation frequencies. In this paper, visual sensitivity to spatial distortions in natural scenes was examined systematically.…”

Adaptation to implied tilt: extensive spatial extrapolation of orientation gradients

“…Adaptation is thought to occur at multiple stages, giving rise to a rich variety of perceptual aftereffects, ranging from distortions of basic stimulus properties such as local orientation (Gibson and Radner, 1937), to more complex higher-level structures (e.g., Suzuki, 2001; Peirce and Taylor, 2006; Anderson et al, 2007; Gheorghiu and Kingdom, 2007). However, surprisingly little is known about the interplay between changes occurring at multiple stages of analysis—a critical component of understanding adaptation in the visual system as a whole.…”