Hillenbrand: Vowels12 Peterson & Barney (1952) Study conducted at Bell Labs. The 1 st big acoustic study carried out with the (then) recently invented sound spectrograph machine. 1. Recordings 10 vowels (i, ɪ, ɛ,æ, ɑ, ɔ, ʊ,u, ʌ, ɚ ) /hVd/ context (“heed,” “hid,” “head,” “had,” etc.) 76 talkers (33 men, 28 women, 15 children) 2. Measurements: F0, F1-F3 3. Listening Study 70 listeners asked to identify each test signal as one of ten words (“heed,” “hid,” “head,” “had,” etc.)
Hillenbrand: Vowels23 What does this mean? It appears as though listeners are recognizing vowels based on information other than F 0 and F 1 -F 3. What are the possibilities? Two Candidates: Duration Patterns of spectral change over time
Hillenbrand: Vowels25 Original Duration Neutral Duration Short Duration Long Duration
Hillenbrand: Vowels26 Logic: If duration plays no role in vowel recognition, the 4 signal types ought to be equally intelligible; i.e., artificially modifying duration will not affect what vowel is heard. On the other hand, if duration plays a role in vowel perception, the OD signals ought to be more intelligible than any of the duration-modified signals. Also, there are specific kinds of changes in vowel identity that we would expect. For example: Shortened /i/ ought to be heard as /I/ Lengthened /I/ ought to be heard as /i/ Shortened /A/ ought to be heard as /‰/ Lengthened / ‰ / ought to be heard as /A/ Shortened /u/ ought to be heard as /U/ Lengthened /U/ ought to be heard as /u/ Shortened /å/ ought to be heard as /ú/ Lengthened /ú/ ought to be heard as /å/
Hillenbrand: Vowels29 Effects of Duration on Vowel Perception Original Duration, Long Duration, Short Duration
Hillenbrand: Vowels30 The Role of Spectral Change in Vowel Perception
Hillenbrand: Vowels31 More examples. Note especially the rise in F2 for /U/ and /ú/.
Hillenbrand: Vowels32 Here’s another way to visualize patterns of formant frequency change in vowels: This figure shows formant frequencies measured at the beginning of the vowel and a 2 nd time at the end of the vowel. (The phonetic symbol is plotted at the 2 nd measurement). Note that some vowels (e.g., /i/ and /u/) are pretty steady over time, but others have formants that change quite a bit throughout the course of the vowel (e.g., /e/, /o/, / ú /, /U/, /A/, /I/ ).
Hillenbrand: Vowels33 NAT:Naturally spoken /hAd/ OF:Synthesized, preserving original formant contours FF:Synthesized with flattened formants
Hillenbrand: Vowels34 Key comparison is OF vs. FF: If the formant movements don’t matter, flattening the formant contour will not affect the vowel percept, and the recognition rates for OF and FF should be very similar. On the other hand, if the formant movements are important, the FF signals will be less intelligible than the OF signals. Conclusion: Spectral change patterns do matter.