1. 1 Speech Perception 3/30/00

2. 2 Speech Perception How do we perceive speech? –Multifaceted process –Not fully understood –Models & theories attempt to explain process Knowledge of speech perception advanced: –Spectrograph Consists of analyzing filters to analyze speech signals Determining acoustic cues for different speech sounds Provides information of fundamental frequency, harmonics, formants of the vocal tract –Pattern playback Speech synthesizer that converts painted visual patterns into speech-like sounds Performs the reverse of the spectrograph Converts visual input into perceived auditory signal

3. 3 Speech Perception Before 1950- Speech was difficult to analyze- laborious analysis systems After 1950- Speech perception became easier to study with spectrogram & pattern playback

4. 4 Speech Perception How we understand the speech of other people. How we select one voice in particular from a crowd. The processes of taking in the acoustic signal of speech and how we reach decisions quickly about who said it, what was said and how it was said.

5. 5 Vowel Perception Formants- –Resonances of the human vocal tract –Acoustic cues for the identification of vowels –The first 2 or 3 formants (F1, F2, F3) are sufficient for the perceptual identification of vowels

6. 6 Diphthong Perception Diphthongs (combinations of 2 vowels) exhibit formant transitions- –Frequency changes in a portion of the formants, reflecting changes in the shape of the vocal tract via articulatory movements

7. 7 Consonant Perception Perception is more complex because consonants depend on vowels for their recognition –I.e. if a stop consonant is separated from vowels they will not be perceived as stops –Stop consonant perception is dependent on rapidly changing formant transitions C to V in a CV context

8. 8 Suprasegmental Perception Suprasegmental (prosodic) features of a language are those properties of speech sounds that appear simultaneously or are overlaid onto the phonetic (segmental) features- I.e. Intonation, stress, quantity timing. Alter the meaning of an utterance

9. 9 Intonation Involves changes in fundamental frequency, perceived as the pitch pattern of a phrase or sentence Can be used to change speaker’s meaning –Declarative sentence (rise-fall intonation) –Questions (end-of-sentence pitch rise) Can use the same words but change the meaning

10. 10 Intonation

11. 11 Stress The perception of stress or the degree of force of an utterance- –Involves 3 acoustic parameters (Intensity, duration and fundamental frequency) –Stressed syllables- Increase in all acoustic parameters –OBject (stress on first syllable- NOUN) –obJECT (stress on second syllable- VERB)

12. 12 Quantity Timing Duration within a phonological system –Changes in relative durations of linguistic units in words can change the meaning of words –Changes in sentence duration can indicate the mood of the speaker

13. 13 Issues in Speech Perception Invariance, Linearity, Segmentation –These issues address the primary recognition problem of: “How the form of a spoken word is recognized from acoustic information in the speech waveform.

14. 14 Acoustic-Phonetic Invariance There is a distinct set of acoustic features corresponding to each phoneme so that each time the phone is produced, the same acoustic features are identified, regardless of context

15. 15 Linearity Proposes that in a spoken word, a specific sound corresponds to each phoneme, with units of sound corresponding to phonemes being discrete and ordered in a particular sequence.

16. 16 Segmentation The speech signal can be divided (and recombined) into acoustically independent units that correspond to specific phonemes.

17. 17 Problems?? 3 principles imply a one-to-one connetion between the acoustic and phonemic properties of sounds in words. NO….Evidence indicates that natural speech does not conform to these conditions! –1. Acoustic cues outnumber phonemes in words –2. Acoustic properties of a phoneme vary in different phonetic contexts. –3. At a given point there may be overlapping of acoustic properties or preceding phones or phones following –4. The articulators move continuously in conversation- coarticulation effects