Direct encoding of orientation variance in the visual system

Abstract

Our perception of regional irregularity, an example of which is orientation variance, seems effortless when we view two patches of texture that differ in this attribute. Little is understood, however, of how the visual system encodes a regional statistic like orientation variance, but there is some evidence to suggest that it is directly encoded by populations of neurons tuned broadly to high or low levels. The present study shows that selective adaptation to low or high levels of variance results in a perceptual aftereffect that shifts the perceived level of variance of a subsequently viewed texture in the direction away from that of the adapting stimulus (Experiments 1 and 2). Importantly, the effect is durable across changes in mean orientation, suggesting that the encoding of orientation variance is independent of global first moment orientation statistics (i.e., mean orientation). In Experiment 3 it was shown that the variance-specific aftereffect did not show signs of being encoded in a spatiotopic reference frame, similar to the equivalent aftereffect of adaptation to the first moment orientation statistic (the tilt aftereffect), which is represented in the primary visual cortex and exists only in retinotopic coordinates. Experiment 4 shows that a neuropsychological patient with damage to ventral areas of the cortex but spared intact early areas retains sensitivity to orientation variance. Together these results suggest that orientation variance is encoded directly by the visual system and possibly at an early cortical stage.

Ensemble perception of color in autistic adults

“…This similarity between the norm‐based coding of faces and that of color has been noted previously [e.g., Webster, ; Webster & Leonard, ]. There is also evidence that observers show adaptation aftereffects to summary statistics—both the mean [size—Corbett, Wurnitsch, Schwartz, & Whitney, ] and also the variance [orientation—Norman, Heywood, & Kentridge, ; spatial position/numerosity—Payzan‐LeNestour, Balleine, Berrada, & Pearson, ]. Such aftereffects suggest that ensemble summary statistics are explicitly represented within the visual system, and may be driven by, and/or contribute to, norm‐based or relative systems of coding.…”

Similarly oriented objects appear more numerous

“…Orientation variance is a directly encoded visual percept and an important cue for discriminating texture and segmenting visual scenes (Dakin, 1999;Dakin & Watt, 1997;Norman et al, 2015). It is not surprising that such a feature would interact with numerosity perception; however, we did not have a strong prior hypothesis that variance or coherence would cause over-or underestimation.…”

“…Indeed, many texture discrimination tasks can be performed by comparing orientation variances (Dakin, 1999). Orientation variance is susceptible to adaptation and adaptation to variance is experimentally distinguishable from adaptation to orientation itself, suggesting that orientation variance is directly encoded and represented by a unique mechanism (Norman, Heywood, & Kentridge, 2015).…”

Texture segmentation without human V4

“…Such an impairment would impact many aspects of perception, from pattern recognition to face perception. It is clear from previous tests on patients MS and HJA, however, that, despite their extensive occipitotemporal damage, neither patient is completely unable to integrate spatially distributed elements -HJA is somewhat spared at estimating mean orientation (Allen et al, 2007) and MS can even discriminate levels of orientation variance (Norman, Heywood & Kentridge, 2015). Such Primary visual cortex is, however, not unique in its apparent sensitivity to texture contrast, and from the current results it is not possible to truly conclude that it is solely primary visual cortex that is responsible for MS's segmentation ability.…”