Psychoacoustics of Dynamic ‘Center-of-Gravity’ Signals

1. Psychoacoustics of Dynamic ‘Center-of-Gravity’ Signals Larry Feth Ashok Krishnamurthy Ohio State University

2. Spectral Center-of-Gravity • Chistovitch and Lublinskaja (1976,1979) • Perceptual Formant at ‘Center-of-Gravity’ • Two-formant synthetic vowel • Matched by adjustable single-formant signal • Center frequency of match depends on relative amplitudes of the two formants

3. Experimental Paradigm

4. Chistovitch and Lublinskaja Results

5. Voelcker Two-tone Signals

6. Voelcker Two-tone Signals • Initially, led to the EWAIF model • Envelope-Weighted Average of Instantaneous Frequency (time domain) • Point by point multiply E x F values • Sum over N periods • Divide by sum of weights • Indicates pitch change in periodic signals • Helmholtz (1954, 2nd English edition) • Jeffress (1964)

7. EWAIF Model

8. IWAIF Model Predictions

9. Two-tone resolution task • Feth and O’Malley (1977) • Two-tone resolution • DI = 1 dB; Df independent variable • ‘Voelcker-tone pair’ pitch discrimination • inverted “u-shaped” psychometric functions • Components resolved beyond –75% point • ~3.5 Bark separation = jnnd

10. Voelcker Signal: Discrimination Task

11. Discrimination Results • Jnnd – ‘Just not noticeable difference’ • Filled circles • Breakpoint estimates • Open circles • CR – critical ratio CBW • CB – ‘empirical’ CBW • Solid line TW envelope

12. IWAIF Model Intensity Weighted Average of Instantaneous Frequency = Centroid of signal’s positive power spectrum (Anantharaman, et al., 1993)

13. Dynamic Center-of-Gravity Effect • Lublinskaja (1996) • Three-formant synthetic Russian vowels • Listeners identified vowels with: • ‘conventional’ formant transitions • co-modulated formant pairs that exhibit the same dynamic spectral center-of-gravity • ID functions were very similar with formant pairs separated by 4.3 Bark or less

14. Psychophysics • Anantharaman (1998) • Two-tone signals with dynamic c-o-g effect • We called them ‘Virtual Frequency’ Glides • Listeners matched transition rates in VF glides to those in FM glides • IWAIF model predicts results for transitions from 2 to ~5 ERB

15. Dynamic Center-of-Gravity Signals Waveform Long-term Spectrum Spectrogram

16. Rate-matching results

17. Model Results

18. Short-term running IWAIF Model

19. IWAIF Model Results

20. Application of ST-IWAIF Model

21. More Psychophysics • Research Question(s) • What is being ‘integrated’ in spectral integration? OR • Where in the auditory system is the processing located?

22. Psychophysics • Iyer, et al., (2001) • Temporal acuity for FM and VF glides • Step vs. linear ramp discrimination • Similar DT values may mean common process • Masking patterns for FM and VF glides • Peripheral process i.e., ‘Energy Masking’ • Different results – VF not peripheral process

23. Temporal Acuity Paradigm Step (red) versus Glide (blue) transitions for FM tone (left panel) and Virtual Frequency (right panel)

24. Temporal Acuity Results Just discriminable step duration for FM (solid lines; filled symbols) and VF (dashed lines; unfilled symbols) signals. Frequency separations are 2, 5 and 8 ERBu. The results for 1000 Hz are represented by circles and those for 4000 Hz by triangles. Average for 4 listeners.

25. Fh Fh Fc Fc Fl Fl Time Time Dynamic Center-of-Gravity Maskers Masking of brief probe by FM glide (left panel) and by VF glide (right panel). Probe is in the spectro-temporal center of each masker. Five auditory filter bands are illustrated.

26. Masking of a 20 ms probe by FM (light blue) and VF (darker blue) maskers. The probe is placed at the beginning, middle, and end of the masker. Significant differences are seen at 5 and 8 ERB for the middle position and the initial position at 8 ERB. Average for 4 listeners. Masking Results

27. Glide Direction Asymmetry • Gordon and Poeppel • 3 Frequency ranges: (for F1,F2 & F3) • ~ 30 unpracticed listeners 20 trials / signal • One interval Direction Identification: Up vs. Dn • Best results at high frequency (F3) range • 10- through 160 ms ‘Up’ is easier to ID than ‘Dn’ • Less clear-cut results at low or mid-freq. ranges

28. Glide Direction Asymmetry Gordon and Poeppel – ARLO (2002) Identification of FM Sweep direction is easier for rising than for falling tones.

29. Glide Direction Asymmetry • Dawson, (2002) • Tested only high frequency range (F3) • Practiced listeners; ~ 100% all conditions! • Modified procedure • Rove each frequency sweep over 1 octave • Practice to ~ asymptote

30. Glide ID Results • Average for 4 listeners • One-interval ID task • 250 trials / datum point • Well-practiced Subj’s • Starting frequency roved over 1-octave range • Summary • FM ‘easier’ than VF • Up ‘easier’ than Down

31. CV Identification Experiment • [da] – [ga] continuum: varying F3 transition • Duration: 50 ms transition into 200 ms base • F3 onset: 2018 to 2658 Hz in 80 Hz steps • F3 base: 2527 Hz (constant) • Formant transition ‘type’: • Klatt synthesizer • Frequency Modulated tone glide • Virtual Frequency glide

32. CV Identification: Stimuli Spectrogram 1. Step 1 of Klatt Monaural Continuum—/ga/ endpoint

33. CV Identification: Stimuli Spectrogram 2. Step 1 of FM Monaural Continuum—/ga/ endpoint

34. CV Identification: Stimuli Spectrogram 3. Step 1 of VF Monaural Continuum—/ga/ endpoint

35. CV Identification: Stimuli Spectrogram 4. Step 1 of Dichotic FM Continuum—/ga/ endpoint

36. CV Identification: Stimuli Spectrogram 5. Step 1 of Dichotic VF Continuum—/ga/ endpoint

37. CV Identification Experiment • Listeners: 8 adults with normal hearing • Procedure: One interval, 2-AFC • 3 transition types: Klatt, FM or VF • 6 of 8 tokens tested • 20 repetitions / token • Results are averaged for the 8 listeners

38. CV Identification: Results

39. CV Identification: Results

40. Psychoacoustics of Dynamic ‘Center-of-Gravity’ Signals Conclusions • ‘Excitation’ is integrated not signal energy • The processing is central not peripheral • Masking Patterns are very different • Temporal Acuity results are similar for FM & VF glides • Direction ID Asymmetry is similar for FM & VF glides

41. Psychoacoustics of Dynamic ‘Center-of-Gravity’ Signals Conclusions • CV identification functions are similar for: • Klatt synthesized sounds • FM formant sounds • VF formant sounds • Thus, it doesn’t matter how ‘excitation’ is moved from A to B, the brain will interpret it as the same sound. • The effect is evident under dichotic listening; further support for central processing.

42. Ewa Jacewicz Rob Fox Nandini Iyer Robin Dawson Jayanth Anantharaman Collaborators

43. Psychoacoustics of Dynamic ‘Center-of-Gravity’ Signals Thank You Questions?

44. Up vs. Down FM Glide

45. Up vs. Down FM Glide

46. Up vs. Down VF Glide

47. Up vs. Down VF Glide

48. Effect of Masker Direction Masking produced by VF (above) and FM (below) maskers with D F = 5 ERB. Purple bars are “up” glides; yellow bars are “down” glides. Centered probe.

49. Effect of Masker Position Masking produced by VF (above) and FM (below) maskers with D F = 5 ERB. Purple bars are “up” glides; yellow bars are “down” glides.

50. Klatt & FM Parameters