Letters lost:capturing appearance in crowded peripheral vision reveals a new kind of masking

Peripheral vision is strongly limited by crowding, the deleterious influence of flanking items on target perception. Distinguishing what is seen from what is merely inferred in crowding is difficult because task demands and prior knowledge may influence observers' reports. Here, we used a standard identification task in which participants were susceptible to these influences, and to minimize them, we used a free-report-and-drawing paradigm. Three letters were presented in the periphery. In Experiment 1, 10 participants were asked to identify the central target letter. In Experiment 2, 25 participants freely named and drew what they saw. When three identical letters were presented, performance was almost perfect in Experiment 1, but it was very poor in Experiment 2, in which most participants reported only two letters. Our study reveals limitations of standard crowding paradigms and uncovers a hitherto unrecognized effect that we call redundancy masking

Multidimensional feature interactions in visual crowding: When configural cues eliminate the polarity advantage.

Crowding occurs when surrounding objects (flankers) impair target perception. A key property of crowding is the weaker interference when target and flankers strongly differ on a given dimension. For instance, identification of a target letter is usually superior with flankers of opposite versus the same contrast polarity as the target (the "polarity advantage"). High performance when target-flanker similarity is low has been attributed to the ungrouping of target and flankers. Here, we show that configural cues can override the usual advantage of low target-flanker similarity, and strong target-flanker grouping can reduce - instead of exacerbate - crowding. In Experiment 1, observers were presented with line triplets in the periphery and reported the tilt (left or right) of the central line. Target and flankers had the same (uniform condition) or opposite contrast polarity (alternating condition). Flanker configurations were either upright (||), unidirectionally tilted (\\ or //), or bidirectionally tilted (\/ or /\). Upright flankers yielded stronger crowding than unidirectional flankers, and weaker crowding than bidirectional flankers. Importantly, our results revealed a clear interaction between contrast polarity and flanker configuration. Triplets with upright and bidirectional flankers, but not unidirectional flankers, showed the polarity advantage. In Experiments 2 and 3, we showed that emergent features and redundancy masking (i.e. the reduction of the number of perceived items in repeating configurations) made it easier to discriminate between uniform triplets when flanker tilts were unidirectional (but not when bidirectional). We propose that the spatial configurations of uniform triplets with unidirectional flankers provided sufficient task-relevant information to enable a similar performance as with alternating triplets: strong-target flanker grouping alleviated crowding. We suggest that features which modulate crowding strength can interact non-additively, limiting the validity of typical crowding rules to contexts where only single, independent dimensions determine the effects of target-flanker similarity

What Line Drawings Reveal About the Visual Brain

Scenes in the real world carry large amounts of information about color, texture, shading, illumination, and occlusion giving rise to our perception of a rich and detailed environment. In contrast, line drawings have only a sparse subset of scene contours. Nevertheless, they also trigger vivid three-dimensional impressions despite having no equivalent in the natural world. Here, we ask why line drawings work. We see that they exploit the underlying neural codes of vision and they also show that artists’ intuitions go well beyond the understanding of vision found in current neurosciences and computer vision

High confidence and low accuracy in redundancy masking.

Visual scenes typically contain redundant information. One mechanism by which the visual system compresses such redundancies is 'redundancy masking' - the reduction of the perceived number of items in repeating patterns. For example, when presented with three lines in the periphery, observers frequently report only two lines. Redundancy masking is strong in radial arrangements and absent in tangential arrangements. Previous studies suggested that redundancy-masked percepts predominate in stimuli susceptible to redundancy masking. Here, we investigated whether strong redundancy masking is associated with high confidence in perceptual judgements. Observers viewed three to seven radially or tangentially arranged lines at 10° eccentricity. They first indicated the number of lines, and then rated their confidence in their responses. As expected, redundancy masking was strong in radial arrangements and weak in tangential arrangements. Importantly, with radial arrangements, observers were more confident in their responses when redundancy masking occurred (i.e., lower number of lines reported) than when it did not occur (i.e., correct number of lines reported). Hence, observers reported higher confidence for erroneous than for correct judgments. In contrast, with tangential arrangements, observers were similarly confident in their responses whether redundancy masking occurred or not. The inversion of confidence in the radial condition (higher confidence when accuracy was low and lower confidence when accuracy was high) suggests that redundancy-masked appearance trumps 'veridical' perception. The often-reported richness of visual consciousness may partly be due to overconfidence in erroneous judgments in visual scenes that are subject to redundancy masking

Appearance changes and error characteristics in crowding revealed by drawings

Peripheral vision is strongly limited by crowding: Targets that are easily recognized in isolation are unrecognizable when flanked by close-by objects. Crowding does not only impair target recognition but also changes appearance. Here we investigated appearance changes and errors in crowding by letting observers draw crowded stimuli. Observers drew stimuli presented at 6° and 12° eccentricity. Stimuli consisted of characters and letter-like symbols. Targets were presented with either a flanker on each side or in isolation. To characterize appearance changes and errors in crowding, we developed a scoring system that captured differences between the drawings and the stimuli. The resulting drawings revealed strong appearance changes under crowding. Importantly, our results reveal crowding errors that are usually not shown in standard crowding paradigms. We found high rates of element Omissions and element Truncations, indicating a central role of target "diminishment" in crowding. Furthermore, we show that a subset of the observed element Omissions and Additions was possibly caused by feature migration. Relatively high rates of position errors, in particular element Translations, reflected the often reported location uncertainty in crowding. Virtually no complete target-flanker substitutions were observed. We suggest a new classification system for errors in crowding, and propose drawing as a useful appearance-based method to investigate crowding

Atypical visual field asymmetries in redundancy masking.

Redundancy masking is the reduction of the perceived number of items in repeating patterns. It shares a number of characteristics with crowding, the impairment of target identification in visual clutter. Crowding strongly depends on the location of the target in the visual field. For example, it is stronger in the upper compared to the lower visual field and is usually weakest on the horizontal meridian. This pattern of visual field asymmetries is common in spatial vision, as revealed by tasks measuring, for example, spatial resolution and contrast sensitivity. Here, to characterize redundancy masking and reveal its similarities to and differences from other spatial tasks, we investigated whether redundancy masking shows the same typical visual field asymmetries. Observers were presented with three to six radially arranged lines at 10° eccentricity at one of eight locations around fixation and were asked to report the number of lines. We found asymmetries that differed pronouncedly from those found in crowding. Redundancy masking did not differ between upper and lower visual fields. Importantly, redundancy masking was stronger on the horizontal meridian than on the vertical meridian, the opposite of what is usually found in crowding. These results show that redundancy masking diverges from crowding in regard to visual field asymmetries, suggesting different underlying mechanisms of redundancy masking and crowding. We suggest that the observed atypical visual field asymmetries in redundancy masking are due to the superior extraction of regularity and a more pronounced compression of visual space on the horizontal compared to the vertical meridian

What crowds in crowding?

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Capsule networks as recurrent models of grouping and segmentation

Funding: AD was supported by the Swiss National Science Foundation grant n.176153 “Basics of visual processing: from elements to figures”. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Data Availability: The human data for experiment 2 and the full code to reproduce all our results are available here: https://github.com/adriendoerig/Capsule-networks-as-recurrent-models-of-grouping-and-segmentation.Peer reviewedPublisher PD