Crowding (mutual scrambling of nearby peripheral stimuli) has several known asymmetries. We explored these and other asymmetries systematically across the visual field. Crowding strength for 16 target (Gabor) positions in the visual field (8 directions × 2 eccentricities) were determined by positioning a plaid mask made of two transparently overlaid Gabors either inward, outward, clockwise, or counter-clockwise around the target. Overall, we found a surprisingly large individual variation in crowding strength appearing as idiosyncratic hotspots across the visual field. No correlations were found between the idiosyncratic variations of crowding and visual acuity either across the visual field or across subjects. When averaged across observers the results replicated most of the previously reported asymmetries of crowding. No new types of asymmetries were observed, but we found that the inward-outward asymmetry of crowding is present only along the horizontal meridian. Most surprisingly, we discovered that this asymmetry increases two-fold, if the observer is forced to attend to both left and right visual fields. This indicates that besides other factors attention allocation has a strong effect on the crowding asymmetry.
It has long been known that an outward mask is much more disruptive than an inward mask in crowding (H. Bouma, 1973). We show that the locus of attention strongly affects this inward-outward anisotropy, removing it in some conditions and reversing it in others. In a 2AFC paradigm, subjects identified whether a high-contrast Gabor target of a given orientation was presented left or right of fixation. When a fixed eccentricity (8°) was used, the outward plaid mask produced much stronger crowding than the inward mask. When 7°, 8°, and 9° eccentricities were interleaved within the same run, diffusing attention, the inward and outward masks produced the same amount of crowding for all three eccentricities. When target identification was contingent on a foveal cue, biasing attention inward, the inward mask produced stronger crowding. Finally, a new contrast-detection paradigm was used to demonstrate that attention is generally mislocalized outward of the target, which may explain the commonly observed anisotropy in crowding. Our results suggest that spatial attention is intimately involved in the mechanism of crowding.
This study extended previous research on equivalence relations established with outcome-specific reinforcers to include the merger of separately established stimulus classes. Participants were four adults. Conditional discriminations AC and BC were trained first. Correct selections of C1 (C2, or C3) in the presence of A1 or B1 (A2 or B2, or A3 or B3) were followed by red (blue, or white) tokens; tokens were exchanged for value added to three participant-selected gift cards. Outcomes on equivalence tests for three-member classes ABC were positive. DF and EF were trained with the same reinforcing consequences, and tests were positive for three-member classes DEF. Results of class merger tests with combinations of stimuli from the ABC and DEF classes (AD, FB, etc.) were immediately positive for two participants, demonstrating six-member classes ABCDEF with reinforcers as nodes. Merger tests for a third participant were initially negative but became positive after brief exposure to unreinforced probe trials with reinforcers as comparison stimuli. Following class merger, tests for matching the reinforcers to samples and comparisons were also positive. Class-merger test results were negative for a fourth participant. The results provide the first demonstration of eight-member equivalence classes including two outcome-specific conditioned reinforcing stimuli.
An important communication skill for children with autism is answering multiple questions about visual stimuli (e.g., "What is it?" "What color is it?"). We targeted answering "What number?" and "What shape?" in the presence of numbers inside shapes, and "What is it?" and "What color?" in the presence of colored objects (e.g., a yellow cat) with 3 preschoolers with autism. In addition to a progressive time delay, we required the participants to answer the questions by echoing a keyword from the questions. For example, we taught them to answer, "What color?" with "color blue." In the context of a multiple-probe design across behaviors within a multipleprobe design across participants, the procedure was effective in increasing trained responses and producing within-and across-category generalization. The echoic may have facilitated the responses by increasing the salience of the auditory stimuli and strengthening intraverbals within autoclitic frames.
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