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Speech perception 2 Perceptual organization of speech.

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Presentation on theme: "Speech perception 2 Perceptual organization of speech."— Presentation transcript:

1 Speech perception 2 Perceptual organization of speech

2 Bottom Line Whether speech is “special” or relies on general perceptual mechanisms, its organization helps to deal with variability in the speech signal and in listening conditions

3 Is speech “special”? Chomsky and language Discovery of variability in the acoustic properties of speech – the normalization problem Discovery of certain perceptual tendencies that make speech seem different from other auditory signals

4 Categorical perception Listeners can only discriminate between sounds that they would identify as belonging to different categories

5 Speech acoustics can be varied along a continuum

6 Identification Was that “ba” or “pa”?

7 Identification functions Voice onset time (ms) Percent “pa” responses 0 5 10 15 20 25 30 35 40 100 50 0 Percent“ba” responses 100 50 0 Category boundary

8 Discrimination Were those the same or different?

9 Discrimination functions Voice onset time (ms) Percent correct 0-5 5-10 10-15 15-20 20-25 25-30 30-35 35-40 100 50 Category boundary

10 Identification v. discrimination functions F1 frequency (Hz) Percent “a” responses 100 50 0 Percent correct 100 50 Category boundary

11 Variability in acoustics: Co-articulation

12 Boundaries shift with the context

13 Why would you have categorical perception? Allows listeners to “ignore” irrelevant variations in speech signal.

14 Is this a special characteristic of speech?

15 Chinchillas also have categorical perception of VOT Kuhl and Miller, 1978

16 Categorical perception of nonspeech sounds Pisoni, 1977

17 Categorical perception of nonspeech sounds Pisoni, 1977

18 Changing the procedure can eliminate categorical discrimination (Pisoni & Lazarus, 1974)

19 Conclusions: categorical perception People tend to hear speech categories, rather than the small acoustic variations across exemplars of the same phoneme. People’s sensitivity at category boundaries reflects general auditory sensitivities, but also depends on memory and other processes. Speech and hearing evolved together: speech takes advantage of our specific auditory sensitivities.

20 Vowel perception not categorical, but continuous

21 Identification v. discrimination functions - vowels F1 frequency (Hz) Percent “a” responses 100 50 0 Percent correct 100 50 Category boundary

22 Effects of experience on speech perception Speech can’t be totally “innate”, because different languages have different phonemic inventories.

23 Example: /r/-/l/ distinction in native speakers of Japanese (Logan et al., 1991)

24 “Theories” accounting for cross- language differences in phonetic perception Infants learn the phonetic contrasts of their native language from scratch. Infants know all of the phonetic contrasts in the world, but they “forget” the ones that they don’t hear around them. Infants know a lot of phonetic contrasts, but the boundaries between phonetic categories shift depending on what they hear.

25 Infants lose the ability to discriminate nonnative contrasts Werker & Tees, 1984

26 Infants lose the ability to discriminate nonnative contrasts (Mattock & Burnham, 2006)

27 Different patterns for different contrasts (Polka, 2001)

28 Vowel perception becomes language specific for infants, but not monkeys (Kuhl, 1991) AdultsInfantsMonkeys 100 80 60 40 20 0 Percent correct Prototype Nonprototype

29 Adults maintain the ability to hear some nonnative distinctions zulu click video

30 People can “relearn” nonnative distinctions (Logan et al., 1991)

31 r l Click 1 Click 2 Click 3 Click 4 g d b k t p a i Prevoiced stops How experience can affect speech perception Perceptual reorganization

32 General Conclusions Auditory sensitivity constrains the phonetic distinctions that we are able to make. Phonetic categories are organized in such a way as to optimize our ability to discriminate and to adapt to changing conditions. Experience with speech sounds reorganizes phonetic categories, and it is the reorganization that makes it difficult to hear phonetic contrasts in the reorganized region.

33 References Best, C. T., McRoberts, G. W., & Sithole, N. M. (1988). EXAMINATION OF PERCEPTUAL REORGANIZATION FOR NONNATIVE SPEECH CONTRASTS - ZULU CLICK DISCRIMINATION BY ENGLISH-SPEAKING ADULTS AND INFANTS. Journal of Experimental Psychology-Human Perception and Performance, 14(3), 345-360. Kuhl, P. K. (1991). HUMAN ADULTS AND HUMAN INFANTS SHOW A PERCEPTUAL MAGNET EFFECT FOR THE PROTOTYPES OF SPEECH CATEGORIES, MONKEYS DO NOT. Perception & Psychophysics, 50(2), 93-107. Kuhl, P. K., & Miller, J. D. (1974). DISCRIMINATION OF SPEECH SOUNDS BY CHINCHILLA - (T) VS (D) IN CV SYLLABLES. J. Acoust. Soc. Am., 56, S52-S52. Logan, J. S., Lively, S. E., & Pisoni, D. B. (1991). TRAINING JAPANESE LISTENERS TO IDENTIFY ENGLISH /R/ AND /1/ - A 1ST REPORT. J. Acoust. Soc. Am., 89(2), 874-886. Mattock, K., & Burnham, D. (2006). Chinese and English infants' tone perception: Evidence for perceptual reorganization. Infancy, 10(3), 241-265. Pisoni, D. B., & Lazarus, J. H. (1974). CATEGORICAL AND NONCATEGORICAL MODES OF SPEECH-PERCEPTION ALONG VOICING CONTINUUM. J. Acoust. Soc. Am., 55(2), 328-333. Polka, L., Colantonio, C., & Sundara, M. (2001). A cross-language comparison of (d)-(male) perception: Evidence for a new developmental pattern. J. Acoust. Soc. Am., 109(5), 2190-2201. Werker, J. F., & Tees, R. C. (1984). CROSS-LANGUAGE SPEECH-PERCEPTION - EVIDENCE FOR PERCEPTUAL REORGANIZATION DURING THE 1ST YEAR OF LIFE. Infant Behavior & Development, 7(1), 49-63.

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