Selective age-related changes in orientation perception

Orientation perception is a fundamental property of the visual system and an important basic processing stage for visual scene perception. Neurophysiological studies have found broader tuning curves and increased noise in orientation-selective neurons of senescent monkeys and cats, results that suggest an age-related decline in orientation perception. However, behavioral studies in humans have found no evidence for such decline, with performance being comparable for younger and older participants in orientation detection and discrimination tasks. Crucially, previous behavioral studies assessed performance for cardinal orientation only, and it is well known that the human visual system prefers cardinal over oblique orientations, a phenomenon called the oblique effect. We hypothesized that age-related changes depend on the orientation tested. In two experiments, we investigated orientation discrimination and reproduction for a large range of cardinal and oblique orientations in younger and older adults. We found substantial age-related decline for oblique but not for cardinal orientations, thus demonstrating that orientation perception selectively declines for oblique orientations. Taken together, our results serve as the missing link between previous neurophysiological and human behavioral studies on orientation perception in healthy aging.</p

Selective age-related changes in orientation perception

Acknowledgments The authors thank Malwina Filipczuk, Leah Hillari, and Jacqueline Von Seth for their help with data collection. Supported by The Rank Prize Funds (JMA, KSP).Peer reviewedPublisher PD

separate motion detecting mechanisms for first and second order patterns revealed by rapid forms of visual motion priming and motion aftereffect

Fast adaptation biases the perceived motion direction of a subsequently presented ambiguous test pattern (R. Kanai & F. A. Verstraten, 2005). Depending on both the duration of the adapting stimulus (ranging from tens to hundreds of milliseconds) and the duration of the adaptation-test blank interval, the perceived direction of an ambiguous test pattern can be biased towards the same or the opposite direction of the adaptation pattern, resulting in rapid forms of motion priming or motion aftereffect respectively. These findings were obtained employing drifting luminance gratings. Many studies have shown that first-order motion (luminance-defined) and second-order motion (contrast-defined) stimuli are processed by separate mechanisms. We assessed whether these effects also exist within the second-order motion domain. Results show that fast adaptation to second-order motion biases the perceived direction of a subsequently presented second-order ambiguous test pattern with similar time courses to that obtained for first-order motion. To assess whether a single mechanism could account for these results, we ran a cross-order adaptation condition. Results showed little or no transfer between the two motion cues and probes, suggesting a degree of separation between the neural substrates subserving fast adaptation of first- and second-order motion. © ARVO

What crowding can tell us about object representations

In crowding, perception of a target usually deteriorates when flanking elements are presented next to the target. Surprisingly, adding further flankers can lead to a release from crowding. In previous work we showed that, for example, vernier offset discrimination at 9� of eccentricity deteriorated when a vernier was embedded in a square. Adding further squares improved performance. The more squares presented, the better the performance, extending across 20� of the visual field. Here, we show that very similar results hold true for shapes other than squares, including unfamiliar, irregular shapes. Hence, uncrowding is not restricted to simple and familiar shapes. Our results provoke the question of whether any type of shape is represented at any location in the visual field. Moreover, small changes in the orientation of the flanking shapes led to strong increases in crowding strength. Hence, highly specific shape-specific interactions across large parts of the visual field determine vernier acuity

What crowding can tell us about object representations

Peer reviewedPublisher PD

Grouping, pooling, and when bigger is better in visual crowding

In crowding, perception of a target is strongly deteriorated by nearby elements. Crowding is often explained by pooling models predicting that adding flankers increases crowding. In contrast, the centroid hypothesis proposes that adding flankers decreases crowding—‘‘bigger is better.’’ In foveal vision, we have recently shown that adding flankers can increase or decrease crowding depending on whether the target groups or ungroups from the flankers. We have further shown how configural effects, such as good and global Gestalt, determine crowding. Foveal and peripheral crowding do not always reveal the same characteristics. Here, we show that the very same grouping and Gestalt results of foveal vision are also found in the periphery. These results can neither be explained by simple pooling nor by centroid models. We discuss when bigger is better and how grouping might shape crowding

When bigger is better

One of the main factors of crowding is the spacing between target and flankers. The closer the flankers are to the target, the stronger is crowding. Recently, it was proposed that crowding strength is determined by the distance between target and flanker centroids (Levi & Carney, 2009). Here, we determined vernier offset discrimination in the periphery with different flanker configurations. When the vernier was flanked by two vertical lines, thresholds increased. Thresholds decreased compared to the two-lines condition when each of the lines was complemented to form a rectangle. This is in line with the centroid hypothesis because the rectangles' centroids are further away than the centroids of the single flankers. However, when crossing the upper and lower horizontal lines of the rectangles, performance deteriorated even though centroids are the same in this and the rectangle condition. These results can neither be explained by the spacing between the target and the flankers nor by centroid distance. Also simple pooling models fail to account for these results. We propose instead that grouping is a key factor in crowding: crowding decreases when target and flankers ungroup, crowding increases when target and flankers group