Abstract
SummaryCrowding is the breakdown in object recognition that occurs in cluttered visual environments [1–4] and the fundamental limit on peripheral vision, affecting identification within many visual modalities [5–9] and across large spatial regions [10]. Though frequently characterized as a disruptive process through which object representations are suppressed [11, 12] or lost altogether [13–15], we demonstrate that crowding systematically changes the appearance of objects. In particular, target patches of visual noise that are surrounded (“crowded”) by oriented Gabor flankers become perceptually oriented, matching the flankers. This was established with a change-detection paradigm: under crowded conditions, target changes from noise to Gabor went unnoticed when the Gabor orientation matched the flankers (and the illusory target percept), despite being easily detected when they differed. Rotation of the flankers (leaving target noise unaltered) also induced illusory target rotations. Blank targets led to similar results, demonstrating that crowding can induce apparent structure where none exists. Finally, adaptation to these stimuli induced a tilt aftereffect at the target location, consistent with signals from the flankers “spreading” across space. These results confirm predictions from change-based models of crowding, such as averaging [16], and establish crowding as a regularization process that simplifies the peripheral field by promoting consistent appearance among adjacent objects.
Highlights
Change-based models are better able to explain the correlation between target identification errors and the structure of flanking elements [9, 16, 22,23,24,25]. These systematic effects could reflect behavioral strategies that, for instance, lead observers to report the average of a stimulus array under conditions of high uncertainty or to report the flankers because of information loss at the target location
We report that crowding induces target noise patches to appear oriented, matching the appearance of flankers to an extent that is indistinguishable from physically oriented stimuli
We examined whether crowding-induced changes in appearance could induce a tilt aftereffect (TAE) by having observers adapt to either (1) an uncrowded target Gabor, (2) crowded noise, or (3) a crowded blank region, followed by a single test Gabor on each trial (Figure 3A)
Summary
MATLAB (MathWorks) on a Macintosh computer running PsychToolbox [49]. Stimuli were presented on a cathode ray tube monitor (LaCie Electron Blue 22) with a resolution of 1152 × 870 pixels and a refresh rate of 75 Hz, fitted with a Bits++ box (Cambridge Research Systems) to give 14-bit contrast resolution. The monitor was calibrated with a Minolta LS110 photometer and linearized with look-up tables to give a mean and maximum luminance of 50 and 100 cd/m2, respectively. Stimuli were viewed monocularly with the dominant eye from a distance of 57 cm. Experiments took place in a dark room, with responses made with either the keyboard (change detection) or mouse (adaptation)
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