What subcortical–cortical relationships tell us about processing speech in noise

Abstract

To advance our understanding of the biological basis of speech-in-noise perception, we investigated the effects of background noise on both subcortical- and cortical-evoked responses, and the relationships between them, in normal hearing young adults. The addition of background noise modulated subcortical and cortical response morphology. In noise, subcortical responses were later, smaller in amplitude and demonstrated decreased neural precision in encoding the speech sound. Cortical responses were also delayed by noise, yet the amplitudes of the major peaks (N1, P2) were affected differently, with N1 increasing and P2 decreasing. Relationships between neural measures and speech-in-noise ability were identified, with earlier subcortical responses, higher subcortical response fidelity and greater cortical N1 response magnitude all relating to better speech-in-noise perception. Furthermore, it was only with the addition of background noise that relationships between subcortical and cortical encoding of speech and the behavioral measures of speech in noise emerged. Results illustrate that human brainstem responses and N1 cortical response amplitude reflect coordinated processes with regards to the perception of speech in noise, thereby acting as a functional index of speech-in-noise perception.

Effects of age and background noise on processing a mistuned harmonic in an otherwise periodic complex sound

“…Presenting auditory stimuli against background noise had little impact on the P1m latency, but significantly increased the N1m and P2m latencies. The noise-related increase in N1m and P2m latencies is consistent with prior studies using speech sounds (Parbery-Clark et al, 2011;Whiting et al, 1998). In the present study, the noise-related increase in N1m and P2m latencies was comparable for the two groups, suggesting that aging and background noise independently affected central auditory processing.…”

“…This finding replicates and extends those of an earlier study to older adults. This noise-induced increase in N1m is not limited to harmonic complexes, but has also been observed for speech sounds (Parbery-Clark et al, 2011;Shtyrov et al, 1999). However, the increase in N1 for sound embedded in low-level noise departs from previous research which has typically reported either no effect or reduced N1 amplitude for signals embedded in noise (e.g., Billings et al, 2009;Hari and Makela, 1988;Morita et al, 2006;Okamoto et al, 2007;Whiting et al, 1998).…”

“…There are several factors that may contribute to this discrepancy, including differences in signal-to-noise ratio, sample sizes, and stimulus types. Interestingly, studies which reported increases in N1 amplitude presented binaural sounds embedded in binaural noise Parbery-Clark et al, 2011;Shtyrov et al, 1999) while those observing reduced amplitude often used monaural stimuli that were presented against either ipsilateral, contralateral, or binaural noise (e.g., Billings et al, 2009;Hari and Makela, 1988;Morita et al, 2006;Okamoto et al, 2007;Whiting et al, 1998). Moreover, in these studies the noise was usually intended to mask the signal whereas in the present study the noise level was not intended to mask the stimuli but rather was used to provide a soft homogenous background against which the transient auditory stimuli were presented.…”

The Impact of Musicianship on the Cortical Mechanisms Related to Separating Speech from Background Noise

“…Like previous studies that presented stimuli in noise (Billings et al, 2009(Billings et al, , 2011Parbery-Clark, Marmel, et al, 2011;Romei et al, Figure 6. (A) Scatterplot illustrating the relationship between accuracy (i.e., percent of words repeated correctly) and P1 amplitude in the SNR-0 condition for musicians and nonmusicians.…”

“…This finding suggests that informational masking (from competing speech signals) and physical/ energetic masking have separable effects, even when attention is directed away from the auditory scene, and demonstrates the unique nature of separating speech from background noise that is also speech. Importantly, the amplitude of the P1 and N1 components is related to the fidelity of the encoding of the speech sound at the level of the brainstem (Parbery-Clark, Marmel, Bair, & Kraus, 2011;Musacchia, Strait, & Kraus, 2008), suggesting that the P1 or N1 may be enhanced in musicians for processing speech in noise.…”