1. WebCT You will find a link to WebCT under the “Current Students” heading on www.uleth.ca. It is your responsibility to know how to work WebCT!www.uleth.ca There is a practice test available online. Log in to WebCT from any computer to take the test if you feel uncomfortable with WebCT (you don’t have to take the test if you don’t want!).

2. The Perception of Speech

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

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

5. Spectrogram reveals differences between phonemes Acoustic Properties of Speech

6. 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?…

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 Then specific phonemes must correspond to specific spectrograms - a property called acoustic-phonetic invariance

8. 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

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/ Clearly perception and understanding of speech sounds is more elaborate than simply interpreting an internal spectrogram Perceiving Speech

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

11. Segmentation is the perception of silence between words Often illusory Perceiving Speech

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

13. So how do you perceive speech?

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

15. 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 Sifts through the Incoming Sound

16. 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 ms. (called voice onset time) –/pa/ is similar except that voice onset time is about 50 ms Categorical Perception

17. 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

18. 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... Listeners will hear either /ba/ or /pa/ but never something in between Categorical Perception

19. 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

20. Categorical Perception is Part of Learning a Language Once category boundaries are learned it is impossible to unlearn them –non-native speakers can often never hear certain phonemes –as a consequence they will always have at least some slight accent

21. Another example: Categorical Perception

22. 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

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

24. 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”.

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

26. 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 !

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

28. The McGurk Effect Cross-modal Integration

29. Next Time: Vision