Reduction in sound discrimination in noise is related to envelope similarity and not to a decrease in envelope tracking abilities.

Humans and animals constantly face challenging acoustic environments such as various background noises that impair the detection, discrimination and identification of behaviorally relevant sounds. Here, we disentangled the role of temporal envelope tracking on the reduction in neuronal and behavioral discrimination between communication sounds in situations of acoustic degradations. By collecting neuronal activity from six different levels of the auditory system, from auditory nerve up to secondary auditory cortex in anesthetized guinea-pigs, we found that tracking of slow changes of the temporal envelope is a general functional property of auditory neurons for encoding communication sounds in quiet and also in adverse, challenging, conditions.
Results from a Go/No-Go sound discrimination task on mice support the idea that the loss of distinct slow envelope cues in noisy conditions impacted the discrimination performance. Together, these results suggest that envelope tracking is potentially a universal mechanism operating in the central auditory system, which allows the detection of any between-stimuli difference in slow envelope and thus cope with degraded conditions.

Reduction in sound discrimination in noise is related to envelope similarity and not to a decrease in envelope tracking abilities. Samira Souffi, Léo Varnet, Meryem Zaidi, Brice Bathellier, Chloé Huetz, Jean-Marc Edeline.

Methods: We simulated auditory nerve fiber (sANF) responses and recorded the neuronal activity in five auditory structures (from cochlear nucleus to secondary auditory cortex) in response to four vocalizations presented in quiet and in two types of noise (a stationary and a chorus noise at three SNRs: +10, 0 and -10 dB). In addition, we tested whether behaving animals can discriminate between whistles when engaged in a Go/No-Go task involving the discrimination between two of the four whistles used in our electrophysiological studies (W1 and W3). Licks to the S+ were rewarded by a drop of water and licks to the S- were punished by a 5-second time-out period.

Results: Subcortical and cortical auditory neurons track the slow changes of the temporal envelope (<20Hz), with a high degree of fidelity in the original (positively correlated with the neuronal discrimination) and degraded conditions. Our results demonstrate that the between-stimulus envelope similarity, which increases in noise, negatively correlates both with the neuronal discrimination and the behavioral performance.

Article published in The Journal of PhysiologyAccess to the manuscript