Neural timing is linked to speech perception in noise

Abstract

Understanding speech in background noise is challenging for every listener, including those with normal peripheral hearing. This difficulty is attributable in part to the disruptive effects of noise on neural synchrony, resulting in degraded representation of speech at cortical and subcortical levels as reflected by electrophysiological responses. These problems are especially pronounced in clinical populations such as children with learning impairments. Given the established effects of noise on evoked responses, we hypothesized that listening-in-noise problems are associated with degraded processing of timing information at the brainstem level. Participants (66 children; ages, 8-14 years; 22 females) were divided into groups based on their performance on clinical measures of speech-in-noise (SIN) perception and reading. We compared brainstem responses to speech syllables between top and bottom SIN and reading groups in the presence and absence of competing multitalker babble. In the quiet condition, neural response timing was equivalent between groups. In noise, however, the bottom groups exhibited greater neural delays relative to the top groups. Group-specific timing delays occurred exclusively in response to the noise-vulnerable formant transition, not to the more perceptually robust, steady-state portion of the stimulus. These results demonstrate that neural timing is disrupted by background noise and that greater disruptions are associated with the inability to perceive speech in challenging listening conditions.

Figure 1.

Top, The stimulus waveform of the speech syllable [da]. Middle, An overlay of grand average brainstem responses (N = 66) to the speech syllable [da] when presented in quiet (gray) and in babble noise (black). Sections of the response corresponding to the stimulus onset, formant transition, and steady-state regions are labeled. Bottom, The same response focused on the onset and transition regions where timing differences between the quiet and noise conditions are most evident. The peaks and troughs used in the analysis have been marked.

Figure 2.

Timing shifts from quiet to noise for top (red heavy line) and bottom (black line) SIN groups. A significant interaction between group and condition was noted (p < 0.01), demonstrating greater noise-induced peak delays in the bottom SIN group. Post hoc analyses indicated significant group by noise effects for peaks 42 (p < 0.01) and 43 (p < 0.01). Inset, Latency interaction between the quiet and noise condition between top and bottom SIN groups for peak 42 (p < 0.01). The latencies are approximately equivalent in the quiet condition, but in noise the responses of the bottom group are significantly delayed. **p < 0.01. Error bars indicate SEM.

Figure 3.

Timing shifts from quiet to noise for top (blue solid) and bottom (black dotted) reading groups. There was a significant main effect of group, and the bottom group had greater overall timing delays than the top reading group. Inset, Latency interaction between the quiet and noise condition between top and bottom reading groups for peak 52. *p < 0.05. Error bars indicate SEM.