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Nathan Destler, Manish Singh, Jacob Feldman; Sensitivity to shape differences along morph spaces. Journal of Vision 2016;16(12):417. doi: https://doi.org/10.1167/16.12.417.
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© ARVO (1962-2015); The Authors (2016-present)
MOTIVATION. We investigated the dimensions defining mental shape space, by measuring shape discrimination thresholds along "morph-spaces" defined by pairs of shapes. Given any two shapes, one can construct a morph-space by taking weighted averages of their boundary vertices (after normalization), creating a continuum of shapes ranging from the first shape to the second. Previous studies of morphs between highly familiar shape categories (e.g. truck and turkey) have shown elevated discrimination at the category boundary, reflecting a kind of "categorical perception" in shape space. Here, we use this technique to explore implicit categorical boundaries in spaces of unfamiliar shapes, where categories are defined not by familiar named types, but by the underlying "generative" structure of mental shape space. METHODS. Subjects were shown two shapes at nearby points along a morph-space, and asked to judge whether they were the same or different, with an adaptive procedure used to estimate discrimination thresholds at each point along the morph-space. We targeted several potentially important categorical distinctions, such one- vs. two-part shapes, two- vs. three-part shapes, changes in symmetry structure, and other "qualitative" distinctions. RESULTS. The results show strong consistency between subjects, as well as some intriguing differences among different morph-spaces. In several spaces, subjects showed marked "categorical" discrimination patterns, with sensitivity (1/difference threshold) maximal at an intermediate point in the morph-space and declining near the two base shapes. However, in other morph-spaces, subjects showed high sensitivity near the base shape with the most symmetries, and declining sensitivity as asymmetry increased. CONCLUSION. The results show that discrimination thresholds are not uniform over shape spaces. Instead, categorical organization of shape spaces influences basic perceptual sensitivity to shape properties.
Meeting abstract presented at VSS 2016
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