Effects of Long-Term Musical Training on Cortical Auditory Evoked Potentials

Abstract

Objective: Evidence suggests that musicians, as a group, have superior frequency resolution abilities when compared with nonmusicians. It is possible to assess auditory discrimination using either behavioral or electrophysiologic methods. The purpose of this study was to determine if the acoustic change complex (ACC) is sensitive enough to reflect the differences in spectral processing exhibited by musicians and nonmusicians.

Design: Twenty individuals (10 musicians and 10 nonmusicians) participated in this study. Pitch and spectral ripple discrimination were assessed using both behavioral and electrophysiologic methods. Behavioral measures were obtained using a standard three interval, forced choice procedure. The ACC was recorded and used as an objective (i.e., nonbehavioral) measure of discrimination between two auditory signals. The same stimuli were used for both psychophysical and electrophysiologic testing.

Results: As a group, musicians were able to detect smaller changes in pitch than nonmusician. They also were able to detect a shift in the position of the peaks and valleys in a ripple noise stimulus at higher ripple densities than non-musicians. ACC responses recorded from musicians were larger than those recorded from non-musicians when the amplitude of the ACC response was normalized to the amplitude of the onset response in each stimulus pair. Visual detection thresholds derived from the evoked potential data were better for musicians than non-musicians regardless of whether the task was discrimination of musical pitch or detection of a change in the frequency spectrum of the ripple noise stimuli. Behavioral measures of discrimination were generally more sensitive than the electrophysiologic measures; however, the two metrics were correlated.

Conclusions: Perhaps as a result of extensive training, musicians are better able to discriminate spectrally complex acoustic signals than nonmusicians. Those differences are evident not only in perceptual/behavioral tests but also in electrophysiologic measures of neural response at the level of the auditory cortex. While these results are based on observations made from normal-hearing listeners, they suggest that the ACC may provide a non-behavioral method of assessing auditory discrimination and as a result might prove useful in future studies that explore the efficacy of participation in a musically based, auditory training program perhaps geared toward pediatric or hearing-impaired listeners.

Figure 1

Box plots illustrate performance by both groups of study participants on a speech perception in noise task (AZ Bio sentence test at 0 dB SNR) and on a timbre identification task.

Figure 2

Box plots show performance of musicians and non-musicians on the spectral ripple and pitch discrimination tasks. The scatter plot shows the correlation between these two behavioral measures of auditory discrimination. Note that better performance on the spectral ripple discrimination task is indicated by higher threshold values while better performance on the pitch discrimination task is indicated by lower thresholds threshold values.

Figure 3

Waveforms recorded from all 20 study participants are shown for two example stimuli. Thinner dashed lines are waveforms recorded from individual participants. The thicker solid lines are grand average waveforms. Waveforms recorded from musicians and non-musicians have been separated. Spectrograms of the stimuli used to evoke these responses are also shown.

Figure 4

Cortical onset and ACC responses recorded from a musician and a non-musician are shown. The upper panels show results evoked using a change in pitch. The parameter is the magnitude of the pitch change. The lower panels show results obtained using a shift in the position of the peaks and valleys of the ripple noise stimuli. The parameter is density of the spectral ripples. The asterisks indicate the visual detection thresholds for the ACC.

Figure 5

The effect of changes in spectral ripple density and pitch on normalized ACC response amplitudes are shown. Filled symbols indicate results obtained from the musicians. Open symbols indicate results obtained from non-musicians. The error bars represent one standard error around the mean. The numbers in parentheses are the number of subjects in each group included in the mean calculation.

Figure 6

Box plots show visual detection thresholds for ACC responses evoked using either a shift in the peaks and troughs of a ripple noise stimulus or a shift in pitch of a musical tone. Results obtained from musicians are contrasted with results recorded from non-musicians. The scatterplot shows the correlation between these two metrics. The line represents the results of a linear regression computed using combined data from both subject groups.

Figure 7

Scatterplots show the relationship between ACC based VDTs and behavioral measures of auditory discrimination for the pitch change and the ripple noise stimuli. The lines show the results of a linear regression computed using combined data from both subject groups. Asterisks indicate responses recorded from individuals with mild hearing loss for frequencies ≥ 4000 Hz.