Abstract
BackgroundAuditory neuropathy is a disorder characterized by no or severely impaired auditory brainstem responses in presence of normal otoacoustic emissions and/or cochlear microphonics. Speech perception abilities in these individuals are disproportionate to their hearing sensitivity and reported to be dependent on cortical evoked potentials and temporal processing abilities. The disproportionate loss of auditory percept in presence of normal cochlear function is suggestive of impairment of auditory neural synchrony.MethodsWe studied the auditory evoked potentials and psychophysical abilities in 14 adults with auditory neuropathy to characterize their perceptual capabilities. Psychophysical tests included measurement of open set speech identification scores, just noticeable difference for transition duration of syllable /da/ and temporal modulation transfer function. Auditory evoked potentials measures were, recording of P1/N1, P2/N2 complex and mismatch negativity (MMN).ResultsResults revealed a significant correlation between temporal processing deficits and speech perception abilities. In majority of individuals with auditory neuropathy P1/N1, P2/N2 complex and mismatch negativity could be elicited with normal amplitude and latency. None of the measured evoked potential parameters correlated with the speech perception scores. Many of the subjects with auditory neuropathy showed normal MMN even though they could not discriminate the stimulus contrast behaviorally.ConclusionConclusions drawn from the study are1. Individuals with auditory neuropathy have severely affected temporal processing.2. The presence of MMN may not be directly linked to presence of behavioral discrimination and to speech perception capabilities at least in adults with auditory neuropathy.
Highlights
Auditory neuropathy is a disorder characterized by no or severely impaired auditory brainstem responses in presence of normal otoacoustic emissions and/or cochlear microphonics
The presence of mismatch negativity (MMN) may not be directly linked to presence of behavioral discrimination and to speech perception capabilities at least in adults with auditory neuropathy
Speech identification scores correlated with low frequency (250 Hz, 500 Hz, 1000 Hz) hearing thresholds (r = 0.67, p = 0.001) but not with the high frequency hearing thresholds (2000 Hz, 4000 Hz and 8000 Hz r = 0.3, p = .234)
Summary
Auditory neuropathy is a disorder characterized by no or severely impaired auditory brainstem responses in presence of normal otoacoustic emissions and/or cochlear microphonics. Speech perception abilities in these individuals are disproportionate to their hearing sensitivity and reported to be dependent on cortical evoked potentials and temporal processing abilities. The disproportionate loss of auditory percept in presence of normal cochlear function is suggestive of impairment of auditory neural synchrony. Auditory neuropathy (AN) is recently described hearing disorder characterized by abnormal auditory nerve functioning in presence of normal cochlear receptor hair cell activity [1]. The clinical findings that define auditory neuropathy are (page number not for citation purposes). Behavioral and Brain Functions 2005, 1:21 http://www.behavioralandbrainfunctions.com/content/1/1/21 SN. ABR identification scores 16/F Present Absent 16/M Present absent
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