Categorical Perception Categorical Perception of Expressions in of Expressions in ChimpanzeesChimpanzees ( (Pan Pan troglodytestroglodytes))

Jennifer M.B. FugateJennifer M.B. FugateMarch 15, 2007March 15, 2007

Many animals spontaneously categorize Many animals spontaneously categorize stimuli in their environment into groupsstimuli in their environment into groups

Categorical perceptionCategorical perception = a process by = a process by which linear physical changes of a which linear physical changes of a stimulus are perceived nonlinearly stimulus are perceived nonlinearly (Harnad, 1987)(Harnad, 1987)

Classification of Classification of StimuliStimuli

BLUE GREEN YELLOW ORANGE RED

Categorical Perception Categorical Perception of Expressionof Expression This is also true for the perception of This is also true for the perception of

facial expressions in humans.facial expressions in humans. One way this has been tested in the One way this has been tested in the

human literature is to use stereotypical human literature is to use stereotypical facial expressions and morph them in facial expressions and morph them in different proportions to see how they are different proportions to see how they are identified.identified.

Humans perceive at least 5 of the 6 Humans perceive at least 5 of the 6 “basic” emotions categorically “basic” emotions categorically (Etcoff & (Etcoff & Magee, 1992; Calder, et al., 1996; de Gelder, et al., 1997).Magee, 1992; Calder, et al., 1996; de Gelder, et al., 1997).

The categorical perception of expression The categorical perception of expression might be beneficial in communicating a might be beneficial in communicating a signaler’s intention (unambiguous signaler’s intention (unambiguous signaling).signaling).

Experiment I: Experiment I: Do chimpanzees perceive their Do chimpanzees perceive their

own expressions categorically?own expressions categorically?

Chimpanzee Chimpanzee ExpressionsExpressions

Pant Hoot Face

Relaxed open mouth “play” Face

Scream Face

Bared Teeth Face

Task 1 – Categorization of Task 1 – Categorization of MorphsMorphs

6 – step morph between bared teeth and play faces

Bared teeth endpoint Play endpoint

1 2 3 4 5 6

Results Task 1Results Task 1Bared Teeth - Play

0.00%10.00%20.00%30.00%40.00%50.00%60.00%70.00%80.00%90.00%

100.00%

morph 1

14% play -86% bt

morph 2(29% play -71% bt

morph 3(43% play -57% bt

morph 4(57% play -43% bt

morph 5(71% play -29% bt

morph 6(86% play -14% bt

Morph

% b

ared

teet

h id

entifi

catio

n

F morph (5,10) = 11.99, p = .001

n.s. n.s. P = .015 P = .015 P

< .001

Task 2 –Within vs. Between Task 2 –Within vs. Between Category DiscriminationCategory Discrimination

WITHIN ONE CATEGORY BETWEEN BOTH CATEGORIES

? ~50%

? ~20%

1 3

4

? ~50%

? ~80%

2

If boundary between 3-4

53

Bared Teeth-Play

30.00%

40.00%

50.00%

60.00%

70.00%

80.00%

1-2-3 2-3-4 3-4-5 4-5-6

Results Task 2Results Task 2

4 looks more like 5 than 3

% sa

mpl

e cla

ssifi

ed a

s low

er

num

ber

Morph triadt between vs. within (3) = 1.842, p = .081

Experiment IIExperiment II Can the identification of a visual Can the identification of a visual

morph be changed depending on morph be changed depending on the accompanying audio?the accompanying audio?

In a nutshell, yes, and the effect In a nutshell, yes, and the effect is generally greatest for morphs is generally greatest for morphs along the categorical boundaries. along the categorical boundaries.

ConclusionsConclusions Chimpanzees likely perceive the Chimpanzees likely perceive the

expressions studied here expressions studied here categorically.categorically.

The addition of auditory The addition of auditory information alters the perception information alters the perception of visual expression.of visual expression.

AcknowledgmentsAcknowledgments Harold Gouzoules, Ph.D.Harold Gouzoules, Ph.D. Lisa Parr, Ph.D. (NIH/NIMH R01-Lisa Parr, Ph.D. (NIH/NIMH R01-

MH068791)MH068791) Yerkes National Primate Research Yerkes National Primate Research

Center (RR-00165)Center (RR-00165) Center for Behavioral Center for Behavioral

Neuroscience (IBS9876754)Neuroscience (IBS9876754)