1 26 September, 2000HKU Categorization Assigning things (percepts, concepts, objects, etc.) to distinct groups in a principled (rule-based) manner.

2 26 September, 2000HKU Categorization and Perception

3 26 September, 2000HKU How do we know what to look for? The world is so full of information...

4 26 September, 2000HKU The world is very complex 1We cannot process all information available to us – we must selectively attend to what is important to us. –How do we know what to attend to? 2We 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?

5 26 September, 2000HKU What determines what we attend to? The environment –Some features of the environment give us necessary information. Our biology –Some aspects of our biology determine what we are capable of attending to. Experience –It turns out that the problem of having to group things together helps us learn what things in the world to attend to.

6 26 September, 2000HKU 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).

7 26 September, 2000HKU 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.

8 26 September, 2000HKU Experience Experience with making categories causes changes in perception. –Acquired equivalence within categories. –Acquired distinctiveness between them. Eleanor Gibson (1969) Robert Goldstone (1998)

9 26 September, 2000HKU Categorical Perception Perceiving a continuous range of stimuli as members of discrete categories. (Harnad, 1987)

10 26 September, 2000HKU Some Physical Continua Color Pitch Loudness Brightness Angle Weight Etc.

11 26 September, 2000HKU Some physical phenomena are perceived continuously

12 26 September, 2000HKU Some are not

13 26 September, 2000HKU For Example A continuum ranging from /da/ to /ga/ (after Delattre, Liberman, & Cooper, 1955) Good /ga/Good /da/

14 26 September, 2000HKU Identification: Discontinuity at Boundary

15 26 September, 2000HKU Pairwise Discrimination: Same or Different?

16 26 September, 2000HKU Pairwise Discrimination (same/different)

17 26 September, 2000HKU What Happened? Physical World Perceptual Representation

18 26 September, 2000HKU Categorical Perception Identification determines Discrimination

19 26 September, 2000HKU Traditional view of CP Discrimination is only possible (above chance) across a category boundary. Within a category, all tokens are perceived as identical.

20 26 September, 2000HKU Another Example Level Tone Continuum Tone 1Tone 6Tone

21 26 September, 2000HKU Identification of tones in context (after Francis, Ciocca, & Ng, in prep)

22 26 September, 2000HKU Pairwise Discrimination (same/different)

23 26 September, 2000HKU Cantonese Tones Show distinct categories in identification. Do not show any evidence of category effect on discrimination. Conclusion (for now): Perception of tone categories does not depend only on changes in perceptual abilities.

24 26 September, 2000HKU Categorical Perception The use of categories in perception is a cognitive process that involves interaction between perceptual information and higher-level knowledge of objects in the world.

25 26 September, 2000HKU What rules are used to group objects? Definitions (Feature Lists) Family Resemblance Similarity to Prototypes Exemplar models

26 26 September, 2000HKU

27 26 September, 2000HKU

28 26 September, 2000HKU Definitions and Features Dogs are animals that have four legs, have fur, bark, wag their tails…

29 26 September, 2000HKU 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.

30 26 September, 2000HKU 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.

31 26 September, 2000HKU Exemplar Models To remember a category, just remember all the members of the category. Head-filling-up problem. Evidence for abstractions.

32 26 September, 2000HKU 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, 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 cat’s striate cortex. Journal of Physiology, 148, Hubel, D. H. & Wiesel, T. N. (1962). Receptive fields, binocular ineraction, and functional architecture in the cat’s visual cortex. Journal of Physiology, 160, 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.