To determine whether the N1-P2 complex reflects training-induced changes in neural activity associated with improved voice-onset-time (VOT) perception.
Auditory cortical evoked potentials N1 and P2 were obtained from 10 normal-hearing young adults in response to two synthetic speech variants of the syllable /ba./ Using a repeated measures design, subjects were tested before and after training both behaviorally and neurophysiologically to determine whether there were training-related changes. In between pre- and post-testing sessions, subjects were trained to distinguish the −20 and −10 msec VOT /ba/ syllables as being different from each other. Two stimulus presentation rates were used during electrophysiologic testing (390 msec and 910 msec interstimulus interval).
Before training, subjects perceived both the −20 msec and −10 msec VOT stimuli as /ba./ Through training, subjects learned to identify the −20 msec VOT stimulus as “mba” and −10 msec VOT stimulus as “ba.” As subjects learned to correctly identify the difference between the −20 msec and −10 msec VOT syllabi, an increase in N1-P2 peak-to-peak amplitude was observed. The effects of training were most obvious at the slower stimulus presentation rate.
As perception improved, N1-P2 amplitude increased. These changes in waveform morphology are thought to reflect increases in neural synchrony as well as strengthened neural connections associated with improved speech perception. These findings suggest that the N1-P2 complex may have clinical applications as an objective physiologic correlate of speech-sound representation associated with speech-sound training.
Department of Speech and Hearing Sciences (K.T., B.O.), University of Washington, Seattle, Washington; Department of Communication Sciences (N.K.), Neurobiology and Physiology, Otolaryngology, Northwestern University, Evanston, Illinois; Department of Communication Sciences (N.K., T.M.), Northwestern University, Evanston, Illinois; and Electrophysiology Department, (C.P.), House Ear Institute, Los Angeles, California.
Portions of this article were presented at the Association for Research in Otolaryngology meeting in St. Petersburg, Florida (2000), and the American Auditory Society meeting in Scottsdale, Arizona (2000).
Address for correspondence: K. Tremblay, Ph.D., Dept. of Speech and Hearing Sciences, University of Washington, 1417 NE 42nd Street, Seattle, WA 98105.
March 23, 2000
October 1, 2000