Color-motion feature-binding errors are mediated by a higher-order chromatic representation

A review of interactions between peripheral and foveal vision

Visual processing varies dramatically across the visual field. These differences start in the retina and continue all the way to the visual cortex. Despite these differences in processing, the perceptual experience of humans is remarkably stable and continuous across the visual field. Research in the last decade has shown that processing in peripheral and foveal vision is not independent, but is more directly connected than previously thought. We address three core questions on how peripheral and foveal vision interact, and review recent findings on potentially related phenomena that could provide answers to these questions. First, how is the processing of peripheral and foveal signals related during fixation? Peripheral signals seem to be processed in foveal retinotopic areas to facilitate peripheral object recognition, and foveal information seems to be extrapolated toward the periphery to generate a homogeneous representation of the environment. Second, how are peripheral and foveal signals re-calibrated? Transsaccadic changes in object features lead to a reduction in the discrepancy between peripheral and foveal appearance. Third, how is peripheral and foveal information stitched together across saccades? Peripheral and foveal signals are integrated across saccadic eye movements to average percepts and to reduce uncertainty. Together, these findings illustrate that peripheral and foveal processing are closely connected, mastering the compromise between a large peripheral visual field and high resolution at the fovea.

Poor peripheral binding depends in part on stimulus color

We have compared two explanations for poor peripheral binding. Binding is the ability to assign the correct features (e.g., color, direction of motion, orientation) to objects. Wu, Kanai, and Shimojo (Nature, 429(6989), 262, 2004) showed that subjects performed poorly on binding dot color with direction of motion in the periphery. Suzuki, Wolfe, Horowitz, and Noguchi (Vision Research, 82, 58-65, 2013) similarly showed that subjects had trouble binding color with line orientation in the periphery. These authors concluded that performance in the periphery was poor because binding is poor in the periphery. However, both studies used red and green stimuli. We tested an alternative hypothesis, that poor peripheral binding is in part due to poor peripheral red/green color vision. Eccentricity-dependent changes in visual processing cause peripheral red/green vision to be worse than foveal vision. In contrast, blue/yellow vision remains centrifugally more stable. We tested 9 subjects in a replication and extension of Suzuki and colleagues' line orientation judgment, in red and green, and in blue and yellow. There were three central conditions: (1) red (or blue) all horizontal, green (or yellow) all vertical; (2) red (or blue) all vertical, green (or yellow) all horizontal; or (3) random pairing of color and orientation. In both the red/green and the blue/yellow color schemes, peripheral performance was influenced by central line orientation, replicating Suzuki and colleagues. However, the effect with blue/yellow lines was smaller, indicating that poor peripheral "binding," as hypothesized by both Wu and colleagues and Suzuki and colleagues, is due in part to their use of red and green stimuli.

Does feature integration affect resolution of multiple simultaneous forms of ambiguity?

Ambiguity resolution, perceptual grouping, and feature integration all occur seamlessly and subconsciously. When multiple regions of an image share ambiguous features, perceptual grouping can yield an integrated object percept rather than one of multiple objects, each with its individual features. Here, perceptual resolution and grouping of chromatically rivalrous Necker cubes were investigated in three experiments to determine the principles that underlie these coherent percepts. The first experiment showed perceptual grouping beyond independent resolution of each cube's color and orientation, but the second experiment did not show grouping greater than expected from separate color- and orientation-grouping processes. The third experiment found no reliable difference in grouping when two features (color and orientation) were part of the same object versus when they were distributed across separate objects. These findings fail to support a role for feature conjunctions in grouping objects with multiple ambiguous features.

Seeing fruit on trees: enhanced perceptual dissimilarity from multiple ambiguous neural representations

Perceptual grouping contributes to the resolution of visual ambiguity of multiple spatially separate regions in view by enhancing their perceptual similarity. Here, the same ambiguous neural representations are shown also to enhance perceived dissimilarity among the regions. Two separated equiluminant gratings were made ambiguous by introducing rivalry for one of two of their features: orientation or chromaticity. Observers perceived two gratings (above and below fixation) to be different in both color and orientation more often than chance. Overall, a disambiguating process was found to select often for maximal perceived dissimilarity between two objects.

Perceptual resolution of ambiguous neural representations for form and chromaticity

A coherent percept of our visual world is important for functioning. Ambiguities, however, are implicit in visual neural representations and must be resolved for stable perception of objects and scenes. Grouping processes can link multiple neurally ambiguous fragments across the visual field. Experiments here determined how multiple visual features of each fragment contribute to perceptual resolution of ambiguity by grouping. Chromatic interocular-switch rivalry, a technique for presenting competing dichoptic images, was used to induce ambiguous neural representations for equiluminant chromatic discs and gratings. Two dichoptic stimuli were presented simultaneously to measure the amount of time they both appeared the same in at least one feature domain. The two stimuli were grouped when they appeared to share ambiguous features such as color, orientation, and spatial frequency more often than chance. Experiments here tested whether unshared and unambiguous features impeded grouping of the ambiguous components. Overall, the results show that grouping can be driven by neural ambiguity that is common for fragments across the visual field, even when the fragments also have other unshared, unambiguous features.

Perceptual resolution of color for multiple chromatically ambiguous objects

In a classic study, Kovács et al. [Proc. Natl. Acad. Sci. USA93, 15508 (1996)PNASA60027-842410.1073/pnas.93.26.15508] used an array of many disks presented dichoptically with half of the disks in one eye "red" and the other half "green;" disk chromaticities in the fellow eye were reversed, resulting in binocular color rivalry for every disk, thus creating color ambiguity. Surprisingly, the binocularly fused percept sometimes was all disks of the same color (red or green), which showed that perceptual resolution of the many ambiguous neural representations did not rely completely on monocular dominance or on independent resolution for each disk. The present study replicates and expands on the original with the aim to isolate binocularly driven neural mechanisms of perceptual resolution without contamination from monocular dominance. Observers viewed a color-rivalrous array with 16 disks presented either steadily to each eye, as in Kovács et al., or with chromatic interocular-switch rivalry (CISR), which swaps the two images between the eyes every 133 ms. The total proportion of viewing time when the 16 disks were perceived to be all red or all green was measured. For three observers, the disks all appeared the same color more often with CISR than with steady rivalrous presentation, suggesting that monocular dominance interferes with grouped perceptual resolution of ambiguous stimuli in the Kovács paradigm. This conclusion was supported by an additional condition using CISR, but with every disk the same color in one eye at each instant (e.g., all "red" disks in one eye and all "green" in the other). This condition was never significantly different from the original CISR condition, as expected if CISR reveals only binocularly mediated perceptual resolution of the disks' color, irrespective of monocular neural representations. In conclusion, chromatically tuned binocularly driven neurons account for perceptual resolution of CISR.