PT - JOURNAL ARTICLE AU - Amarins N. Heeringa AU - Christine Köppl TI - Auditory nerve fiber discrimination and representation of naturally-spoken vowels in noise AID - 10.1523/ENEURO.0474-21.2021 DP - 2022 Jan 24 TA - eneuro PG - ENEURO.0474-21.2021 4099 - http://www.eneuro.org/content/early/2022/01/24/ENEURO.0474-21.2021.short 4100 - http://www.eneuro.org/content/early/2022/01/24/ENEURO.0474-21.2021.full AB - To understand how vowels are encoded by auditory nerve fibers, a number of representation schemes have been suggested that extract the vowel’s formant frequencies from auditory nerve-fiber spiking patterns. The current study aims to apply and compare these schemes for auditory nerve-fiber responses to naturally-spoken vowels in a speech-shaped background noise. Responses to three vowels were evaluated; based on behavioral experiments in the same species, two of these were perceptually difficult to discriminate from each other (/e/vs/i/) and one was perceptually easy to discriminate from the other two (/a:/).Single-unit auditory nerve fibers were recorded from ketamine/xylazine-anesthetized Mongolian gerbils of either sex (n = 8). First, single-unit discrimination between the three vowels was studied. Compared to the perceptually easy discriminations, the average spike timing-based discrimination values were significantly lower for the perceptually difficult vowel discrimination. This was not true for an average rate-based discrimination metric, the rate d-prime. Consistently, spike timing-based representation schemes, plotting the temporal responses of all recorded units as a function of their best frequency, i.e. dominant component schemes, average localized interval rate, and fluctuation profiles, revealed representation of the vowel’s formant frequencies, whereas no such representation was apparent in the rate-based excitation pattern.Making use of perceptual discrimination data, this study reveals that discrimination difficulties of naturally-spoken vowels in speech-shaped noise originate peripherally and can be studied in the spike timing patterns of single auditory nerve fibers.Significance statementUnderstanding speech in noisy environments is an everyday challenge. This study investigates how single auditory nerve fibers, recorded in the Mongolian gerbil, discriminate and represent naturally-spoken vowels in a noisy background approximating real-life situations. Neural discrimination metrics were compared to the known behavioral performance by the same species, comparing easy to difficult vowel discriminations. A spike-timing-based discrimination metric agreed well with perceptual performance, while mean discharge rate was a poor predictor. Furthermore, only spike-timing-based, but not the rate-based, representation schemes revealed peaks at the formant frequencies, which are paramount for perceptual vowel identification and discrimination. This study reveals that vowel discrimination difficulties in noise originate peripherally and can be studied in the spike-timing patterns of single auditory nerve fibers.