The role of color and attention-to-color in mirror-symmetry perception

Abstract

The role of color in the visual perception of mirror-symmetry is controversial. Some reports support the existence of color-selective mirror-symmetry channels, others that mirror-symmetry perception is merely sensitive to color-correlations across the symmetry axis. Here we test between the two ideas. Stimuli consisted of colored Gaussian-blobs arranged either mirror-symmetrically or quasi-randomly. We used four arrangements: (1) ‘segregated’ – symmetric blobs were of one color, random blobs of the other color(s); (2) ‘random-segregated’ – as above but with the symmetric color randomly selected on each trial; (3) ‘non-segregated’ – symmetric blobs were of all colors in equal proportions, as were the random blobs; (4) ‘anti-symmetric’ – symmetric blobs were of opposite-color across the symmetry axis. We found: (a) near-chance levels for the anti-symmetric condition, suggesting that symmetry perception is sensitive to color-correlations across the symmetry axis; (b) similar performance for random-segregated and non-segregated conditions, giving no support to the idea that mirror-symmetry is color selective; (c) highest performance for the color-segregated condition, but only when the observer knew beforehand the symmetry color, suggesting that symmetry detection benefits from color-based attention. We conclude that mirror-symmetry detection mechanisms, while sensitive to color-correlations across the symmetry axis and subject to the benefits of attention-to-color, are not color selective.

The role of motion and number of element locations in mirror symmetry perception

“…However, this level of performance is similar to those obtained by previous studies1253. Our results show that static patterns have a higher detection threshold than moving patterns, but only when one single pattern is presented throughout.…”

“…Symmetry perception elicits a distinctive pattern of brain activity9, involving a large network of extrastriate visual areas such V3a, V7 and LOC1011. Although several recent studies have examined the contribution of simple visual attributes, such as colour121314 and stereoscopic depth151617 to symmetry perception, little if any, is known about the role of motion in symmetry perception. In dynamic scenes, both motion direction and timing are likely to affect symmetry perception.…”

The neural basis of visual symmetry and its role in mid‐ and high‐level visual processing

“…For instance, in the case of luminance antisymmetry, all elements are arranged symmetrically, but black elements are paired with white and white with black. Antisymmetry and symmetry are perceptually comparable under some conditions, in particular when density is low, but in other cases antisymmetry discrimination is impaired . There are a few explanations for the relative perceptual weakness of antisymmetry.…”

“…Wu and Chen and Gheorghiu et al . studied the relationship between symmetry and luminance or color of the elements.…”

Symmetric patterns with different luminance polarity (anti‐symmetry) generate an automatic response in extrastriate cortex

“…It seems that the extrastriate symmetry network is flexible enough to feed on a range of color or luminance‐defined features. However, it prefers such features to be matched at symmetrical positions (see also Gheorghiu et al., for equivalent behavioral results and interpretation).…”