Degraded temporal processing after traumatic brain injury

Hearing complaints are common following traumatic brain injury (TBI) even in the absence of peripheral auditory impairment. Study goals were to explore the mechanisms which underlie this complaint. Adult listeners with a history of mild TBI or concussion were compared to young and age-matched controls. All listeners had normal or near-normal audiometric thresholds. Listeners with TBI reported difficulty understanding speech in noise. We hypothesized that hearing complaints after TBI are related to damage to neural pathways resulting in degraded temporal resolution. A battery of psychophysical tasks were used to test this hypothesis, specifically: monaural temporal fine structure, to evaluate temporal coding of unresolved harmonics; binaural temporal fine structure, to evaluate temporal coding of a low-frequency sinusoid; interaural coherence, to evaluate sensitivity to the similarity of a correlated broadband noise; and masking level difference, to evaluate the ability to take advantage of interaural phase for tone detection in noise. Results showed individual differences in temporal processing ability among listeners with a history of TBI. Test scores varied from normal to significantly impaired, despite normal audiometry. These results suggest that auditory temporal processing may be related to difficulty understanding speech in noise after TBI. [Work supported by NIH.]