Dissociable Perceptual Effects of Visual Adaptation

Abstract

Neurons in the visual cortex are responsive to the presentation of oriented and curved line segments, which are thought to act as primitives for the visual processing of shapes and objects. Prolonged adaptation to such stimuli gives rise to two related perceptual effects: a slow change in the appearance of the adapting stimulus (perceptual drift), and the distortion of subsequently presented test stimuli (adaptational aftereffects). Here we used a psychophysical nulling technique to dissociate and quantify these two classical observations in order to examine their underlying mechanisms and their relationship to one another. In agreement with previous work, we found that during adaptation horizontal and vertical straight lines serve as attractors for perceived orientation and curvature. However, the rate of perceptual drift for different stimuli was not predictive of the corresponding aftereffect magnitudes, indicating that the two perceptual effects are governed by distinct neural processes. Finally, the rate of perceptual drift for curved line segments did not depend on the spatial scale of the stimulus, suggesting that its mechanisms lie outside strictly retinotopic processing stages. These findings provide new evidence that the visual system relies on statistically salient intrinsic reference stimuli for the processing of visual patterns, and point to perceptual drift as an experimental window for studying the mechanisms of visual perception.

Distinct mechanism for long-term contrast adaptation

“…In the retina, a rapid process that occurs within 100 ms of a stimulus differs in mechanism from longerterm adaptation (28), and similar, dissociable, very rapid adaptation is evident in motion-selective area MT, where it plays a role in motion perception (29). The prior behavioral work reviewed above is also consistent with separate shorter-term mechanisms of contrast adaptation acting over seconds and minutes (22,23), as is additional behavioral work suggesting that contrast adaptation may be controlled by multiple mechanisms, but that was not concerned with the temporal properties of those mechanisms (30). Hence, the adaptation measured here likely represents the action of mechanisms near the long end of a continuous distribution across timescales.…”

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

“…Some aftereffects, such as those induced by tilt adaptation, seem to arise primarily from contrastive processes, in which adaptation exaggerates differences between the adaptor and subsequent other stimuli without changing the adaptor's appearance (Mitchell and Muir (1976); but see Müller, Schillinger, Do, and Leopold (2009) and Chapter 2). Other aftereffects, such as those induced by adaptation to colour saturation, seem to arise from renormalisation processes in which a prolonged adaptor comes to appear more 'neutral' during exposure.…”

“…In the domain of orientation perception, the consensus tips in favour of a multichannel representation of orientation, giving rise to a predominantly locally repulsive tilt aftereffect, but this remains controversial (see Müller, Schillinger, et al (2009) and Chapter 2). In the domain of shape perception, a norm-based theory of aspect ratio encoding has been proposed (Regan & Hamstra, 1992;Suzuki, 2005), although there is little relevant evidence from aftereffects to support or falsify this.…”

“…However, data from a new psychophysical method devised by Müller, Schillinger, et al (2009) appear to provide clear evidence for normalisation. Müller, Schillinger, et al (2009) (Müller, Schillinger, et al, 2009).…”

“…However, some data suggest that there might be a small renormalising component in addition to the predominant local repulsion (Held, 1963;Müller, Schillinger, et al, 2009;Prentice & Beardslee, 1950;Templeton, 1972;Vaitkevicius et al, 2009). In Chapter 2, I address the most compelling recent evidence for tilt renormalisation (Müller, Schillinger, et al, 2009) and show that it can be explained instead by an interaction between the experimental task, and observers' uneven discrimination sensitivity in the orientation domain. (a) Blue curves depict the responsiveness of channels before adaptation; each channel is selective for a relatively narrow range of stimulus values, and the value of zero plays no special role in encoding.…”