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Categorization
Assigning things (percepts, concepts,
objects, etc.) to distinct groups in a
principled (rule-based) manner.
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Categorization and
Perception
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26 September, 2000 HKU 3How do we know what to look for?
The world is so full of information...
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The world is very complex
1 We cannot process all information available to us
we must selectively attendto what is important
to us.
How do we know what to attend to?
2 We cannot keep track of every individual item in
the world we must group similar things
together. What rules are used to group objects, and how do these
rules operate?
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Environment
The Horizon ratio.
Most people see the
buildings as the same
size, and the tower as
taller.
The ratio above to
below the horizon
always gives good
information about
height (except in
illusions).
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Our Biology
Neural detectors for perceptual
properties
Vision: Horizontal lines, vertical lines,dots, directional motion, retinal location
(Hubel & Wiesel, 1959, 1962); also color,
brightness, simple shapes & solids, etc. Audition: loudness, pitch, frequency
sweeps.
Etc.
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Experience
Experience with making categories
causes changes in perception.
Acquired equivalence within categories.
Acquired distinctiveness between them.
Eleanor Gibson (1969)
Robert Goldstone (1998)
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Categorical Perception
Perceiving a continuous range
of stimuli as members of
discrete categories.
(Harnad, 1987)
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Some Physical Continua
Color
Pitch
Loudness
Brightness
Angle
Weight
Etc.
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Some physical phenomena
are perceived continuously
0
20
40
60
80
100
0 1 2 3 4 5 6 7 8 9 10
Magnitude of Stimulus(e.g. Loudness)
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Some are not
010
20304050
607080
90100
0 1 2 3 4 5 6 7 8 9 10
token
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For Example
A continuum ranging from
/da/ to /ga/
(after Delattre, Liberman, & Cooper, 1955)
Good /ga/Good /da/
1 2 3 4 5 6 7 8
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Identification:
Discontinuity at Boundary
010
20304050
607080
90100
1 2 3 4 5 6 7 8
token
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Pairwise Discrimination:
Same or Different?
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Pairwise Discrimination
(same/different)
0
1020
30
40
50
6070
80
90
100
1_2 2_3 3_4 4_5 5_6 6_7 7_8
Pair of stimuli
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What Happened?
1 2 3 4 5 6 7 8
1 2 3 4 5 6 7 8
Physical World
Perceptual Representation
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Categorical Perception
Identification
determinesDiscrimination
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Traditional view of CP
Discrimination is only possible
(above chance) across a category
boundary.
Within a category, all tokens are
perceived as identical.
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Another Example
Level Tone Continuum
Tone 1Tone 6 Tone 3
1 2 3 4 5 6 7 8 9 10
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Identification of tones in
context(after Francis, Ciocca, & Ng, in prep)Identification
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1 2 3 4 5 6 7 8 9 10
Stimulus
low
mid
high
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Pairwise Discrimination
(same/different)Level tone discrimination
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1_2 2_3 3_4 4_5 5_6 6_7 7_8 8_9 9_10
Stimulus pair
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Cantonese Tones
Show distinct categories in
identification.
Do not show any evidence ofcategory effect on discrimination.
Conclusion (for now): Perception of
tone categories does not dependonly on changes in perceptual
abilities.
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Categorical Perception
The use of categories in perception
is a cognitive process that involves
interaction between perceptualinformation and higher-level
knowledge of objects in the world.
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What rules are used to
group objects?
Definitions (Feature Lists)
Family Resemblance
Similarity to Prototypes
Exemplar models
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Definitions and Features
Dogs are animals that have four legs,
have fur, bark, wag their tails
Animal Four legs Fur Barks Wags tail
Banyan Tree X X X X X
Goldish X X X X
Persian Cat X X
German Shepherd
Dachshund
Mexican Hairless X
Barking Deer ?
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Family Resemblance
Ludwig Wittgenstein (1953) proposed
that games could not be defined or
categorized by features. Rather, any game shares some
resemblance to some (but not all)
other games.
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Similarity to Prototypes
Rosch (1978). Prototype is a central,
average, representation (real or
constructed) of a category. Tokens sufficiently similar to the
prototype are considered members
of that category. Memory for specific exemplars.
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Exemplar Models
To remember a category, just
remember all the members of the
category. Head-filling-up problem.
Evidence for abstractions.
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Bibliography
Francis, A. L., Ciocca, V. & Ng, B. K. C. (in prep). On the noncategorical perception of
Cantonese tones.
Gibson, E. J. (1969). Principles of Perceptual Learning and Development. New York,
Appleton-Century-Crofts.
Goldstone, R. (1998). Perceptual learning. Annual Review of Psychology, 49, 585-
612. Harnad, S. (1987). Psychophysical and cognitive aspects of categorical perception: A
critical overview. In Harnad, S. (Ed.) Categorical Perception: The Groundwork of
Cognition. Cambridge, MA, The MIT Press.
Hubel, D. H. & Wiesel, T. N. (1959). Receptive fields of single neurones in the cats
striate cortex. Journal of Physiology, 148, 574-591.
Hubel, D. H. & Wiesel, T. N. (1962). Receptive fields, binocular ineraction, and
functional architecture in the cats visual cortex. Journal of Physiology, 160, 106-154.
Rosch, E. (1978). Principles of categorization. In Rosch, E. & Lloyd, B. (Eds.)
Cognition and Categorization. Hillsdale, NJ, Lawrence Erlbaum Associates.
Wittgenstein, L. (1953). Philosophical Investigations. New York, Macmillan.