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Stimulus Presentation Strategies for Eliciting the Acoustic Change Complex: Increasing Efficiency

Martin, Brett A.1; Boothroyd, Arthur2; Ali, Dassan3; Leach-Berth, Tiffany3

doi: 10.1097/AUD.0b013e3181ce6355
Research Articles
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Objective: The purpose of this study was to compare four strategies for stimulus presentation in terms of their efficiency when generating a speech-evoked cortical acoustic change complex (ACC) in adults and children.

Design: Ten normally hearing adults (aged 22 to 31 yrs) and nine normally hearing children (aged 6 to 9 yrs) served as participants. The ACC was elicited using a 75-dB SPL synthetic vowel containing 1000 Hz changes of second formant frequency, creating a change of perceived vowel between /u/ and /i/. The ACC was recorded from Cz using four stimulus formats:

  1. Interrupted presentation of a 1-sec stimulus containing a single change from /u/ to /i/ using a 2-sec interonset interval.
  2. Interrupted presentation of the same stimulus using a 1-sec interonset interval.
  3. Interrupted presentation of a 1.5-sec stimulus containing a change from /u/ to /i/ followed by a reverse change from /i/ to /u/, using a 2-sec interonset interval.
  4. Continuous presentation of a stimulus alternating between /u/ and /i/ using a 1-sec repetition interval.

Interrupted presentation of a 1-sec stimulus containing a single change from /u/ to /i/ using a 2-sec interonset interval.Interrupted presentation of the same stimulus using a 1-sec interonset interval.Interrupted presentation of a 1.5-sec stimulus containing a change from /u/ to /i/ followed by a reverse change from /i/ to /u/, using a 2-sec interonset interval.Continuous presentation of a stimulus alternating between /u/ and /i/ using a 1-sec repetition interval. ACC magnitude was expressed as the standard deviation of the voltage waveform within a window believed to span the ACC. Noise magnitude was estimated from the variances at each sampling point in the same window. Efficiency was expressed in terms of the ACC to noise magnitude ratio divided by testing time.

Results: ACC magnitude was not significantly different for the two directions of second formant change. Reducing interonset interval from 2 to 1 sec increased efficiency by a factor close to two. Combining data from the two directions of change increased efficiency further, by a factor approximating the square root of 2.

Conclusion: Continuous alternating stimulus presentation is more efficient than interrupted stimulus presentation in eliciting the ACC. The benefits of eliminating silent periods and doubling the number of acoustic changes presented in a given time period are not seriously offset by a reduction in root mean square response amplitude, at least in young adults and in children as young as 6 yrs.

This study examined four strategies for stimulus presentation in terms of their efficiency when generating a speech-evoked cortical acoustic change complex (ACC) in adults and children. Continuous alternating stimulus presentation is more efficient than interrupted stimulus presentation in eliciting the ACC. The benefits of eliminating silent periods and doubling the number of acoustic changes presented in a given time period, are not seriously offset by a reduction in rms response amplitude, at least in young adults and in children as young as 6 years old.

1Program in Speech-Language-Hearing Sciences, Graduate Center of the City University of New York, New York, New York; 2Distinguished Professor Emeritus, Program in Speech-Language-Hearing Sciences, Graduate Center of the City University of New York, New York, New York; 3Program in Audiology, Montclair State University, Upper Montclair, New Jersey.

Portions were used in partial fulfillment for the requirements of the Sc.D. degree at Montclair State (D.A. and T.B.).

Supported by NIH-NIDCD grant #DC05386 (to B.A.M.).

Address for correspondence: Brett A. Martin, Program in Speech and Hearing Sciences, Graduate Center, City University of New York, 365 Fifth Avenue, New York, NY 10016. E-mail: bmartin@gc.cuny.edu.

Received March 24, 2009; accepted November 13, 2009.

© 2010 Lippincott Williams & Wilkins, Inc.