Context-dependent encoding in the auditory brainstem subserves enhanced speech-in-noise perception in musicians

Abstract

Musical training strengthens speech perception in the presence of background noise. Given that the ability to make use of speech sound regularities, such as pitch, underlies perceptual acuity in challenging listening environments, we asked whether musicians' enhanced speech-in-noise perception is facilitated by increased neural sensitivity to acoustic regularities. To this aim we examined subcortical encoding of the same speech syllable presented in predictable and variable conditions and speech-in-noise perception in 31 musicians and nonmusicians. We anticipated that musicians would demonstrate greater neural enhancement of speech presented in the predictable compared to the variable condition than nonmusicians. Accordingly, musicians demonstrated more robust neural encoding of the fundamental frequency (i.e., pitch) of speech presented in the predictable relative to the variable condition than nonmusicians. The degree of neural enhancement observed to predictable speech correlated with subjects' musical practice histories as well as with their speech-in-noise perceptual abilities. Taken together, our findings suggest that subcortical sensitivity to speech regularities is shaped by musical training and may contribute to musicians' enhanced speech-in-noise perception.

Fig. 1

To investigate subcortical sensitivity to stimulus regularities, the speech sound /da/ was presented in predictable (top) and variable (bottom) conditions. In the predictable condition, /da/ was presented 100% of the time. In the variable condition, /da/ was randomly presented at a frequency of 12.5%, in the context of seven other speech sounds. Auditory brainstem responses to /da/ were event-matched between the two conditions (represented by highlighted bars) so as to avoid the potential confound of presentation order.

Fig. 2

Subcortical enhancement of predictable speech in musicians. (A) Group average responses for musicians (left) and nonmusicians (right) in predictable (grey) and variable (black) stimulus conditions. (B) Grand average spectra and (C) corresponding frequency amplitude bar graphs for the predictable and variable conditions for the fundamental frequency (F₀) and its harmonics (H₂–H₅). (D) Musicians, but not nonmusicians, demonstrate enhanced subcortical representation of the fundamental frequency (F₀) in the predictable condition relative to the variable condition. *p < 0.05; **p < 0.01; error bars represent 1 standard error.

Fig. 3

The difference between the F₀ representation in the predictable compared to the variable condition (F_0predictable – F_0variable) correlates with speech-in-noise perception among musicians, in which greater subcortical sensitivity to speech regularities relates to better speech-in-noise perception (rho = −0.567, p = 0.02). This same relationship is not present in the nonmusician group (rho = −0.348, p = 0.204).

Fig. 4

The difference between the F₀ representations in the predictable compared to the variable condition (F_0predictable – F_0variable) correlates with years of musical practice for the musician group. The more years musicians consistently practiced their instrument, the greater the neural sensitivity to speech sound regularities (rho = 0.672, p = 0.004).