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Categorical Perception of Expressions in Chimpanzees ( Pan troglodytes )

Categorical Perception of Expressions in Chimpanzees ( Pan troglodytes ). Jennifer M.B. Fugate March 15, 2007. Classification of Stimuli. Many animals spontaneously categorize stimuli in their environment into groups

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Categorical Perception of Expressions in Chimpanzees ( Pan troglodytes )

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  1. Categorical Perception of Expressions in Chimpanzees (Pan troglodytes) Jennifer M.B. Fugate March 15, 2007

  2. Classification of Stimuli • Many animals spontaneously categorize stimuli in their environment into groups • Categorical perception = a process by which linear physical changes of a stimulus are perceived nonlinearly (Harnad, 1987) GREEN YELLOW ORANGE RED BLUE

  3. Categorical Perception of Expression • This is also true for the perception of facial expressions in humans. • One way this has been tested in the human literature is to use stereotypical facial expressions and morph them in different proportions to see how they are identified. • Humans perceive at least 5 of the 6 “basic” emotions categorically (Etcoff & Magee, 1992; Calder, et al., 1996; de Gelder, et al., 1997). • The categorical perception of expression might be beneficial in communicating a signaler’s intention (unambiguous signaling).

  4. Experiment I: • Do chimpanzees perceive their own expressions categorically?

  5. Chimpanzee Expressions Relaxed open mouth “play” Face Scream Face Bared Teeth Face Pant Hoot Face

  6. Task 1 – Categorization of Morphs 1 2 3 4 5 6 6 – step morph between bared teeth and play faces Bared teeth endpoint Play endpoint

  7. Results Task 1 Bared Teeth - Play n.s. n.s. P = .015 100.00% P = .015 P < .001 90.00% 80.00% 70.00% 60.00% % bared teeth identification 50.00% 40.00% 30.00% 20.00% 10.00% 0.00% morph 1 morph 2 morph 3 morph 4 morph 5 morph 6 (29% play - (43% play - (57% play - (71% play - (86% play - 14% play - 71% bt 57% bt 43% bt 29% bt 14% bt 86% bt Morph F morph (5,10) = 11.99, p = .001

  8. Task 2 –Within vs. Between Category Discrimination 2 4 ? ~20% ? ~50% ? ~80% ? ~50% 1 3 5 3 BETWEEN BOTH CATEGORIES WITHIN ONE CATEGORY If boundary between 3-4

  9. Bared Teeth-Play 80.00% 70.00% 60.00% 50.00% 40.00% 30.00% 1-2-3 2-3-4 3-4-5 4-5-6 Results Task 2 4 looks more like 5 than 3 % sample classified as lower number Morph triad t between vs. within (3) = 1.842, p = .081

  10. Experiment II • Can the identification of a visual morph be changed depending on the accompanying audio? • In a nutshell, yes, and the effect is generally greatest for morphs along the categorical boundaries.

  11. Conclusions • Chimpanzees likely perceive the expressions studied here categorically. • The addition of auditory information alters the perception of visual expression.

  12. Acknowledgments • Harold Gouzoules, Ph.D. • Lisa Parr, Ph.D. (NIH/NIMH R01-MH068791) • Yerkes National Primate Research Center (RR-00165) • Center for Behavioral Neuroscience (IBS9876754)

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