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)