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Categorical Perception

Categorical Perception. March 27, 2013. Don’t Forget!. Interim course project report #5 is due on Monday, April 1 st !. Testing the Theory. The earliest experiments on place perception were conducted in the 1950s, using a speech synthesizer known as the pattern playback.

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Categorical Perception

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  1. Categorical Perception March 27, 2013

  2. Don’t Forget! • Interim course project report #5 is due on Monday, April 1st!

  3. Testing the Theory • The earliest experiments on place perception were conducted in the 1950s, using a speech synthesizer known as the pattern playback.

  4. Pattern Playback Picture

  5. Haskins Formant Transitions • Testing the perception of two-formant stimuli, with varying F2 transitions, led to a phenomenon known as categorical perception.

  6. Categorical Perception • Categorical perception = • continuous physical distinctions are perceived in discrete categories. • In the in-class experiment from last time: • There were 11 different syllable stimuli • They only differed in the locus of their F2 transition • F2 Locus range = 726 - 2217 Hz • Source: http://www.ling.gu.se/~anders/KatPer/Applet/index.eng.html

  7. Stimulus #1 Stimulus #6 Stimulus #11 Example stimuli from the in-class experiment.

  8. Identification • In Categorical Perception: • All stimuli within a category boundary should be labeled the same.

  9. Discrimination • Original task: ABX discrimination • Stimuli across category boundaries should be 100% discriminable. • Stimuli within category boundaries should not be discriminable at all. In practice, categorical perception means: the discrimination function can be determined from the identification function.

  10. Identification  Discrimination • Let’s consider a case where the two sounds in a discrimination pair are the same. • Example: the pair is stimulus 3 followed by stimulus 3 • Identification data--Stimulus 3 is identified as: • [b] 95% of the time • [d] 5% of the time • The discrimination pair will be perceived as: • [b] - [b] - .95 * .95 = .9025 • [d] - [d] - .05 * .05 = .0025 • Probability of same response is predicted to be: • (.9025 + .0025) = .905 = 90.5%

  11. Identification  Discrimination • Let’s consider a case where the two sounds in a discrimination pair are different. • Example: the pair is stimulus 9 followed by stimulus 11 • Identification data: • Stimulus 9: [d] 80% of the time, [g] 20% of the time • Stimulus 11: [d] 5% of the time, [g] 95% of the time • The discrimination pair will be perceived as: • [d] - [d] - .80 * .05 = .04 • [g] - [g] - .20 * .95 = .19 • Probability of same response is predicted to be: • (.04 + .19) = 23%

  12. Discrimination • In this discrimination graph-- • Solid line is the observed data • Dashed line is the predicted data • (on the basis of the identification scores) Note: the actual listeners did a little bit better than the predictions.

  13. Categorical, Continued • Categorical Perception was also found for VOT distinctions. • And for stop/glide/vowel distinctions: 10 ms transitions: [b] percept 60 ms transitions: [w] percept 200 ms transitions: [u] percept

  14. Interpretation • Main idea: in categorical perception, the mind translates an acoustic stimulus into a phonemic label. (category) • The acoustic details of the stimulus are discarded in favor of an abstract representation. • A continuous acoustic signal: • Is thus transformed into a series of linguistic units:

  15. The Next Level • Interestingly, categorical perception is not found for non-speech stimuli. • Miyawaki et al: tested perception of an F3 continuum between /r/ and /l/.

  16. The Next Level • They also tested perception of the F3 transitions in isolation. • Listeners did not perceive these transitions categorically.

  17. The Implications • Interpretation: we do not perceive speech in the same way we perceive other sounds. • “Speech is special”… • and the perception of speech is modular. • A module is a special processor in our minds/brains devoted to interpreting a particular kind of environmental stimuli.

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