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It has previously been reported that visual crowding of a target by flankers is stronger in the upper visual field than in the lower, and this finding has been attributed to greater attentional resolution in the lower hemifield (He, Cavanagh, & Intriligator, 1996). Here we show that the upper/lower asymmetry in visual crowding can be explained by natural variations in the borders of each individual's visual field. Specifically, asymmetry in crowding along the vertical meridian can be almost entirely accounted for by replacing the conventional definition of visual field location, in units of degrees of visual angle, with a definition based on the ratio of the extents of an individual's upper and lower visual field. We also show that the upper/lower crowding asymmetry is eliminated when stimulus eccentricity is expressed in units of percentage of visual field extent but is present when the conventional measure of visual angle is used. We further demonstrate that the relationship between visual field extent and perceptual asymmetry is most evident when participants are able to focus their attention on the target location. These results reveal important influences of visual field boundaries on visual perception, even for visual field locations far from those boundaries., (© 2015 ARVO.)

A new illusion, called the configural shape illusion (CSI), is described in which the apparent shape of an object (the "target") is systematically distorted by the presence of an adjacent shape (the "inducer") that is distinct from, but perceptually grouped with, the target. The target is selectively elongated in a direction consistent with the extension of the larger configuration that includes both target and inducer. Experiments 1 and 2 show that the CSI magnitude varies systematically with factors known to influence grouping strength between configural elements, including proximity, good continuation, positional alignment, lightness similarity, hue similarity, and common fate. Experiments 3 through 5 examine the influence of relative inducer size and target size on illusion magnitude. We suggest that the CSI is caused by edge assimilation modulated by similarity between the target and inducer arising from population coding of edge positions. This assimilation account fits well with previous explanations of one-dimensional illusions of linear extent (e.g., the Müller-Lyer and Baldwin illusions), which are extended to account for the present two-dimensional illusion of shape., (© 2014 ARVO.)

Shifts of attention due to rapid cue onsets have been shown to distort the perceived location of objects, but are there also systematic distortions in the perceived shapes of the objects themselves from such shifts? The present study demonstrates that there are. In three experiments, oval contours were presented that varied in width and height. Two brief, bright white dots were presented as cues and were positioned horizontally or vertically either inside or outside the oval contour. Observers had to judge whether the oval was taller than wide. The results show that the perceived shape of an oval was changed by visual cues such that the oval contours were repelled by the cues (Exp. 1). This effect only occurred when the cues preceded the ovals, providing sufficient time between the presentations to attract involuntary attention (Exp. 2). Moreover, an explanation based on figural aftereffects was ruled out (Exp. 3).

Reliable effects of spatial attention on perceptual measures have been well documented, yet little is known about how attention affects perception of space per se. The present study examined the effects of involuntary shifts of spatial attention on perceived location using a paradigm developed by S. Suzuki and P. Cavanagh (1997) that produces an attentional repulsion effect (ARE). The ARE refers to the illusory displacement of two vernier lines away from briefly presented cues. In Experiment 1, we show that the magnitude of the ARE depends on cue-target distance, indicating that the effects of attention on perceived location are not uniform across the visual field. Experiments 2 and 3 tested whether repulsion occurs away from cue center of mass or from cue contour. Perceived repulsion always occurred away from the cues' center of mass, regardless of the arrangement of the cue contours relative to the vernier lines. Moreover, the magnitude of the ARE varied with shifts in the position of the cues' center of mass. These experiments suggest that the onset of the cue produces a shift of attention to its center of mass rather than to the salient luminance contours that define it, and that this mechanism underlies the ARE.