Abstract
Perceptual categorization is a fundamental cognitive process that gives meaning to an often graded sensory environment. Previous research has subdivided the visual pathway into posterior regions that processes the physical properties of a stimulus, and frontal regions that process more abstract properties such as category information. The superior temporal sulcus (STS) is known to be involved in face and emotion perception, but the nature of its processing remains unknown. Here, we used targeted fMRI measurements of the STS to investigate whether its representations of facial expressions are categorical or noncategorical. Multivoxel pattern analysis showed that even though subjects were performing a categorization task, the left STS contained graded, noncategorical representations. In the right STS, representations showed evidence for both stimulus-related gradations and a categorical boundary.
Highlights
Perceptual categorization is a fundamental cognitive ability because it underlies the recognition of abstract, behaviorally relevant classes in an often graded sensory environment
Percent anger Reaction time (s) functional magnetic resonance imaging (fMRI) RESULTS We trained a SMLR classifier to distinguish the neural representation associated with 0% anger from the neural representation associated with 100% anger
In this study we showed that the multivoxel representations of facial expressions in the left superior temporal sulcus (STS) are graded and noncategorical
Summary
Perceptual categorization is a fundamental cognitive ability because it underlies the recognition of abstract, behaviorally relevant classes in an often graded sensory environment. There is evidence for a frontal-posterior division of labor for visual categorization (Freedman et al, 2001, 2003; Op de Beeck et al, 2001). Experiments on the inferior temporal cortex (ITC) of nonhuman primates have shown that as the shape of a stimulus moves parametrically away from the a neuron’s preferred shape, the neuron’s response decreases in a graded manner (Op de Beeck et al, 2001). Consistent with the evidence from nonhuman primates, fMRI adaptation studies on humans have shown mostly noncategorical tuning for specific shapes in lateral occipital cortex (LOC), but tuning for categories in lateral PFC (Jiang et al, 2007).
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