1. The Perception of Speech

2. Speech is for rapid communication Speech is composed of units of sound called phonemes –examples of phonemes: /ba/ in bat, /pa/ in pat Speech

3. Seeing Sound with Spectrograms A spectrogram is a 3D plot of sound Time Frequency

4. Seeing Sound with Spectrograms A spectrogram is a 3D plot of sound Time Frequency Intensity Intensity is often coded by colour

5. Speech can be characterized by a spectrogram Acoustic Properties of Speech

6. Spectrogram reveals differences between phonemes The differences are in the formants and the formant transitions Acoustic Properties of Speech

7. Perceiving Speech So perceiving (interpreting) speech sounds is simply a matter of matching the spectrotemporal properties (the shape of the spectrogram) of the incoming sound waves to the appropriate phoneme right?…

8. Perceiving Speech So perceiving (interpreting) speech sounds is simply a matter of matching the spectrotemporal properties (the shape of the spectrogram) of the incoming sound waves to the appropriate phoneme Then specific phonemes must correspond to specific spectrograms - a property called acoustic-phonetic invariance

9. Acoustic - Phonetic invariance says that phonemes should match one and only one pattern in the spectrogram –This is not the case! For example /d/ followed by different vowels: Perceiving Speech

10. Acoustic - Phonetic invariance says that phonemes should match one and only one pattern in the spectrogram –This is not the case! For example /d/ Clearly perception and understanding of speech sounds is more elaborate than simply interpreting an internal spectrogram Perceiving Speech

11. The phrase “Peter buttered the burnt toast” has five /t/ phonemes. There are not 5 identical sweeps in the spectrogram Perceiving Speech

12. The Segmentation Problem Segmentation is the perception of silence between words Often illusory Perceiving Speech

13. The phrase “I owe you a Yo-Yo” has no silence in it ! Perceiving Speech

14. Spoken Input The Segmentation Problem: –The stream of acoustic input is not physically segmented into discrete phonemes, words, phrases, etc. –Silent gaps don’t always indicate (aren’t perceived as) interruptions in speech

15. Spoken Input The Segmentation Problem: –The stream of acoustic input is not physically segmented into discrete phonemes, words, phrases, etc. –Continuous speech stream is sometimes perceived as having gaps

16. Perceiving Speech So how do you perceive speech? Some of the “strategies”: 1. reduce the data 2. use context clues 3. use vision

17. Categorical Perception is a phenomenon in which the brain assigns a stimulus into one or another category but never into an intermediate category Categorical Perception

18. For example, /ba/ and /pa/ differ in their formant transitions –/ba/ is formed by stopping the flow of air from the lungs and releasing it after about 10 milliseconds (called voice onset time) –/pa/ is similar except that voice onset time is about 50 ms Categorical Perception

19. Voice onset time can range from zero to >50 ms. For example, you could synthesize a sound with a voice onset time of 30 ms but... Categorical Perception

20. Voice onset time can range from zero to >50 ms. For example, you could synthesize a sound with a voice onset time of 30 ms but... English speakers will hear either /ba/ or /pa/ but never something in between Categorical Perception

21. Categorical Perception is Part of Learning a Language Babies can discriminate /ba/ from /pa/ and can discriminate these from phonemes with intermediate voice onset times! By 10 to 12 months, babies (learning English) stop discriminating intermediate voice onset times

22. Categorical Perception is Part of Learning a Language Once category boundaries are learned it is impossible to unlearn them –non-native speakers of any language often cannot hear certain phonemes the way native speakers do –as a consequence they will always have at least some slight accent

23. Another example: Categorical Perception

24. Perception (of all types) Makes Use of Context The stream of information contained in speech is usually ambiguous and incomplete Your brain makes a “best guess” based on the circumstances

25. Perception (of all types) Makes Use of Context Consider the following example: “The __eel fell of the cough shoe”. car”.

26. Perception (of all types) Makes Use of Context Consider the following example: Listeners report hearing the “appropriate” phoneme during the cough “The __eel fell of the cough shoe”. car”.

27. Why rely on only one sensory system when there is information in two !? Much of Speech Perception isn’t Auditory !

28. Why rely on only one sensory system when there is information in two !? The brain seamlessly integrates any information it is given - this is called cross- modal integration Much of Speech Perception isn’t Auditory !

29. Speech perception involves the synthesis of vision and hearing The McGurk effect demonstrates the critical role of vision on speech perception Cross-modal Integration

30. The McGurk Effect Cross-modal Integration

31. The McGurk Effect - suggests that visual and auditory information are combined to enhance speech perception under normal circumstances When visual and auditory information are incongruous the resulting perception is unpredictable and often wrong Cross-modal Integration

32. Next Time: Taste Smell Touch Balance