Representations of a perceptual space of visual textures
Two representations of a high-dimensional perceptual space
Jonathan D. Victor, Syed M. Rizvi, and Mary M. Conte
Vision Research 137, 1-23 (2017)
Abstract
A perceptual space is a mental workspace of points in a sensory domain that supports
similarity and difference judgments and enables further processing such as classification and
naming. Perceptual spaces are present across sensory modalities; examples include colors, faces,
auditory textures, and odors. Color is perhaps the best-studied perceptual space, but it is atypical
in two respects. First, the dimensions of color space are directly linked to the three cone
absorption spectra, but the dimensions of generic perceptual spaces are not as readily traceable to
single-neuron properties. Second, generic perceptual spaces have more than three dimensions.
This is important because representing each distinguishable point in a high-dimensional space by
a separate neuron or population is unwieldy; combinatorial strategies may be needed to
overcome this hurdle.
To study the representation of a complex perceptual space, we focused on a well-characterized
10-dimensional domain of visual textures. Within this domain, we determine
perceptual distances in a threshold task (segmentation) and a suprathreshold task (border salience
comparison). In N=4 human observers, we find both quantitative and qualitative differences
between these sets of measurements. Quantitatively, observers' segmentation thresholds were
inconsistent with their uncertainty determined from border salience comparisons. Qualitatively,
segmentation thresholds suggested that distances are determined by a coordinate representation
with Euclidean geometry. Border salience comparisons, in contrast, indicated a global curvature
of the space, and that distances are determined by activity patterns across broadly tuned
elements. Thus, our results indicate two representations of this perceptual space, and suggest that
they use differing combinatorial strategies.
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