Projects | People | Publications | Downloads

David Purcell

• Purcell, D. W., Ross, B., Picton, T. W. and Pantev, C. (2007). Cortical responses to the 2f1-f2 combination tone measured indirectly using magnetoencephalography. Journal of the Acoustical Society of America 122(2)992-1003.

• Purcell, D. W. and K. Munhall (2006). Adaptive control of vowel formant frequency: Evidence from real-time formant manipulation. Journal of the Acoustical Society of America 120(2), 966-977.

• Purcell, D. W., P. Van Roon , M. S. John , and T. Picton (2006). Simultaneous Latency Estimations for Distortion Product Otoacoustic Emissions and Envelope Following Responses. Journal of the Acoustical Society of America 119(5), 2869-2880.

• Purcell, D. W. and K. Munhall (2006). Compensation Following Real-time Manipulation of Formants in Isolated Vowels. Journal of the Acoustical Society of America 119(4), 2288-2297.

Abstracts

Cortical responses to the 2f1-f2 combination tone measured indirectly using magnetoencephalography

The simultaneous presentation of two tones with frequencies f1 and f2 causes the perception of several combination tones in addition to the original tones. The most prominent of these are at frequencies f2-f1 and 2f1-f2. This study measured human physiological responses to the 2f1-f2 combination tone at 500 Hz caused by tones of 750 and 1000 Hz with intensities of 65 and 55 dB SPL, respectively. Responses were measured from the cochlea using the distortion product otoacoustic emission (DPOAE), and from the auditory cortex using the 40-Hz steady-state magnetoencephalographic (MEG) response. The perceptual response was assessed by having the participant adjust a probe tone to cause maximal beating (�best-beats�) with the perceived combination tone. The cortical response to the combination tone was evaluated in two ways: first by presenting a probe tone with a frequency of 460 Hz at the perceptual best-beats level, resulting in a 40-Hz response because of interaction with the combination tone at 500 Hz, and second by simultaneously presenting two f1 and f2 pairs that caused combination tones that would themselves beat at 40 Hz. The 2f1-f2 DPOAE in the external auditory canal had a level of 2.6 (s.d. 12.1) dB SPL. The 40-Hz MEG response in the contralateral cortex had a magnitude of 0.39 (s.d. 0.1) nA m. The perceived level of the combination tone was 44.8 (s.d. 11.3) dB SPL. There were no significant correlations between these measurements. These results indicate that physiological responses to the 2f1-f2 combination tone occur in the human auditory system all the way from the cochlea to the primary auditory cortex. The perceived magnitude of the combination tone is not determined by the measured physiological response at either the cochlea or the cortex.

[top]

Adaptive control of vowel formant frequency: Evidence from real-time formant manipulation

Auditory feedback during speech production is known to play a role in speech sound acquisition and is also important for the maintenance of accurate articulation. In two studies the first formant (F1) of monosyllabic consonant-vowel-consonant words (CVCs) was shifted electronically and fed back to the participant very quickly so that participants perceived the modified speech as their own productions. When feedback was shifted up (experiment 1 and 2) or down (experiment 1) participants compensated by producing F1 in the opposite frequency direction from baseline. The threshold size of manipulation that initiated a compensation in F1 was usually greater than 60 Hz. When normal feedback was returned, F1 did not return immediately to baseline but showed an exponential deadaptation pattern. Experiment 1 showed that this effect was not influenced by the direction of the F1 shift, with both raising and lowering of F1 exhibiting the same effects. Experiment 2 showed that manipulating the number of trials that F1 was held at the maximum shift in frequency (0, 15, 45 trials) did not influence the recovery from adaptation. There was a correlation between the lag-one autocorrelation of trial-to-trial changes in F1 in the baseline recordings and the magnitude of compensation. Some participants therefore appeared to more actively stabilize their productions from trial-to-trial. The results provide insight into the perceptual control of speech and the representations that govern sensorimotor coordination

[top]

Simultaneous Latency Estimations for Distortion Product Otoacoustic Emissions and Envelope Following Responses

The purpose of this research was to simultaneously estimate processing delays in the cochlea and brainstem using the same acoustic stimuli. Apparent latencies were estimated from ear canal measurements of 2f1-f2 distortion product otoacoustic emissions (DPOAEs), and scalp recordings of the f2-f1 envelope following response (EFR). The stimuli were equal level tone pairs (65 dB SPL) with the upper tone f2 set at either 900 or 1800 Hz to fix the initiation site of the DPOAE and EFR. The frequency of f1 was swept continuously between frequency limits chosen to keep the EFR response between 150 and 170 Hz. The average DPOAE latencies were 9.6 and 6.2 ms for f2 =900 and 1800 Hz, and the corresponding EFR latencies were 12.4 and 8.8 ms. In a control condition, a third (suppressor) tone was added near the DPOAE response frequency to evaluate whether the potential source at fdp was contributing significantly to the measured emission. DPOAE latency is the sum of both inward and outward cochlear delays. The EFR apparent latency is the sum of inward cochlear delay and neural processing delay. Neural delay was estimated as approximately 5.3 ms for both frequencies of stimulation.

[top]

Compensation Following Real-time Manipulation of Formants in Isolated Vowels

Auditory feedback influences human speech production, as demonstrated by studies using rapid pitch and loudness changes. Feedback has also been investigated using the gradual manipulation of formants in adaptation studies with whispered speech. In the work reported here, the first formant of steady-state isolated vowels was unexpectedly altered within trials for voiced speech. This was achieved using a real-time formant tracking and filtering system developed for this purpose. The first formant of vowel /eh/ was manipulated 100% toward either /�/ or /I/, and participants responded by altering their production with average F1 compensation as large as 16.3% and 10.6% of the applied formant shift, respectively. Compensation was estimated to begin <460 ms after stimulus onset. The rapid formant compensations found here suggest that auditory feedback control is similar for both F0 and formants.

[top]

Other NCA labs include

Anechoic Chamber | Assistive Devices | Child Amplification |
Child Hearing Research | Digital Signal Processing | Speech Communication | Electrophysiology | Hearing Research Clinic | Hearing Science  | Robert B. Johnston Aural Rehabilitations