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Reading chimpanzee faces: evidence for the role of verbal labels in categorical perception of emotion.

ABSTRACT: Categorical perception (CP) occurs when continuously varying stimuli are perceived as belonging to discrete categories. Thereby, perceivers are more accurate at discriminating between stimuli of different categories than between stimuli within the same category (Harnad, 1987; Goldstone, 1994). The current experiments investigated whether the structural information in the face is sufficient for CP to occur. Alternatively, a perceiver's conceptual knowledge, by virtue of expertise or verbal labeling, might contribute. In two experiments, people who differed in their conceptual knowledge (in the form of expertise, Experiment 1; or verbal label learning, Experiment 2) categorized chimpanzee facial expressions. Expertise alone did not facilitate CP. Only when perceivers first explicitly learned facial expression categories with a label were they more likely to show CP. Overall, the results suggest that the structural information in the face alone is often insufficient for CP; CP is facilitated by verbal labeling.

SUBMITTER: Fugate JM

PROVIDER: S-EPMC2949420 | biostudies-literature | 2010 Aug

REPOSITORIES: biostudies-literature

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Reading chimpanzee faces: evidence for the role of verbal labels in categorical perception of emotion.

Fugate Jennifer M B JM Gouzoules Harold H Barrett Lisa Feldman LF

Emotion (Washington, D.C.) 20100801 4

Categorical perception (CP) occurs when continuously varying stimuli are perceived as belonging to discrete categories. Thereby, perceivers are more accurate at discriminating between stimuli of different categories than between stimuli within the same category (Harnad, 1987; Goldstone, 1994). The current experiments investigated whether the structural information in the face is sufficient for CP to occur. Alternatively, a perceiver's conceptual knowledge, by virtue of expertise or verbal labeli ...[more]

PMID: 20677871

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Project description:BackgroundWhile humans (like other primates) communicate with facial expressions, the evolution of speech added a new function to the facial muscles (facial expression muscles). The evolution of speech required the development of a coordinated action between visual (movement of the lips) and auditory signals in a rhythmic fashion to produce "visemes" (visual movements of the lips that correspond to specific sounds). Visemes depend upon facial muscles to regulate shape of the lips, which themselves act as speech articulators. This movement necessitates a more controlled, sustained muscle contraction than that produced during spontaneous facial expressions which occur rapidly and last only a short period of time. Recently, it was found that human tongue musculature contains a higher proportion of slow-twitch myosin fibers than in rhesus macaques, which is related to the slower, more controlled movements of the human tongue in the production of speech. Are there similar unique, evolutionary physiologic biases found in human facial musculature related to the evolution of speech?Methodology/prinicipal findingsUsing myosin immunohistochemistry, we tested the hypothesis that human facial musculature has a higher percentage of slow-twitch myosin fibers relative to chimpanzees (Pan troglodytes) and rhesus macaques (Macaca mulatta). We sampled the orbicularis oris and zygomaticus major muscles from three cadavers of each species and compared proportions of fiber-types. Results confirmed our hypothesis: humans had the highest proportion of slow-twitch myosin fibers while chimpanzees had the highest proportion of fast-twitch fibers.Conclusions/significanceThese findings demonstrate that the human face is slower than that of rhesus macaques and our closest living relative, the chimpanzee. They also support the assertion that human facial musculature and speech co-evolved. Further, these results suggest a unique set of evolutionary selective pressures on human facial musculature to slow down while the function of this muscle group diverged from that of other primates.

Dataset Information

Reading chimpanzee faces: evidence for the role of verbal labels in categorical perception of emotion.

Publications

Reading chimpanzee faces: evidence for the role of verbal labels in categorical perception of emotion.

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