September 2015
Volume 15, Issue 12
Vision Sciences Society Annual Meeting Abstract  |   September 2015
Visual search speed is influenced by differences in shape arbitrariness
Author Affiliations
  • Anna Leshinskaya
    Psychology Department, Harvard University
  • Alfonso Caramazza
    Psychology Department, Harvard University
Journal of Vision September 2015, Vol.15, 1165. doi:
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      Anna Leshinskaya, Alfonso Caramazza; Visual search speed is influenced by differences in shape arbitrariness. Journal of Vision 2015;15(12):1165.

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      © ARVO (1962-2015); The Authors (2016-present)

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We hypothesized that the visual system is particularly tuned to those features which correlate with behaviorally relevant dimensions, and compared a few possibilities: how man-made an object is (naturalness), how often an object is eaten (edibility), how often an object is manipulated (manipulability), and the degree to which an object’s shape is arbitrary (shape arbitrariness; Prasada, 2001). For example, the shape of a hammer is more constrained by the kind of thing that it is (i.e., is less arbitrary) than the shape of a rock. Does variability in perceptual similarity among sets of small, inanimate objects correlate with behavioral ratings on any of these dimensions? We chose four sets (categories) of stimuli: manipulable artifacts (e.g., pens), non-manipulable artifacts (e.g., lamps), natural objects (e.g. pinecones), and fruits/vegetables. These categories did not differ on ratings of typicality, familiarity, internal details, and visual complexity, or in area, aspect ratio, contour variance, extent, spatial frequency, contrast, or luminance. Participants searched for a target image among distractors from the same or different category; they pressed a space bar when they found the target, and reported its location by clicking X’s that replaced the original images. For each category pairing, the difference in search speeds between same- and different-category trials was taken as an index of perceptual dissimilarity, and correlated with distances in each dimension for each subject (representational similarity analysis). Neither manipulability nor edibility explained the pattern of perceptual dissimilarity among categories (all r< .1, t< 1,p>.3). Although naturalness explained some variance (r=.16, t=2.13, p=.048), shape arbitrariness explained more (r=.40, t=4.05, p< .0001). Visual features correlated with shape arbitrariness include shape symmetry and regularity, according to ratings(r=.74, p< .001). These results suggest that, among inanimate objects, the visual system may be particularly sensitive to the perceptual features correlated with the arbitrariness of their shapes.

Meeting abstract presented at VSS 2015


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