Speech-in-noise discriminability after noise exposure: Insights from a gerbil model of acoustic trauma

Exposure to loud sounds can lead to hearing impairments. Speech comprehension, especially in the presence of background sounds, allegedly declines as a consequence of noise-induced hearing loss. However, the connection between noise overexposure and deteriorated speech-in-noise perception is not clear yet and potential underlying mechanisms are still under debate. This study investigates speech-in-noise discrimination in young-adult Mongolian gerbils before and after an acoustic trauma to reveal possible noise-induced changes in the perception of speech sounds and to examine the commonly suggested link between noise exposure and speech-in-noise perception difficulties. Nine young-adult gerbils were trained to discriminate a deviant consonant-vowel-consonant combination (CVC) or vowel-consonant-vowel combination (VCV) in a sequence of CVC or VCV standards, respectively. The logatomes were spoken by different speakers and masked by a steady-state speech-shaped noise. After the gerbils completed the behavioral baseline experiments, they underwent an acoustic trauma and collected data for the second time in the behavioral experiments. Applying multidimensional scaling, response latencies were used to generate perceptual maps reflecting the gerbils internal representations of the sounds pre- and post-trauma. To evaluate how the discrimination of vowels and consonants was altered after the acoustic trauma, changes in response latencies between phoneme pairs were investigated with regard to their articulatory features. Auditory brainstem responses were measured to assess peripheral auditory function. We found that the perceptual maps of vowels and consonants were very similar before and after noise exposure. Interestingly, the gerbils overall vowel discrimination ability was improved after the acoustic trauma, even though the gerbils suffered from noise-induced hearing loss. In contrast to the improvements in vowel discrimination, there were only minor changes in the gerbils ability to discriminate consonants. Moreover, the noise exposure showed a differential influence on the response latencies for vowel and consonant discriminations depending on the articulatory features of the specific phonemes.