Abstract
The objective of this experiment was to address: 1) whether normal efferent system function is required for normal cochlear tuning as measured by distortion product otoacoustic emission (DPOAE) suppression in humans and 2) whether cochlear function, assessed by DPOAE suppression tuning, is normal in a small group of patients with auditory neuropathy. DPOAE suppression tuning curves (STCs) are similar to other physiologic measures of tuning. They are generated by evoking a DPOAE with two simultaneously presented pure tones and then suppressing the distortion product with a third tone of varying frequency and level. In this study, DPOAE STCs were generated with f2 frequencies of 1500, 3000, and 6000 Hz in 15 normal-hearing adults and four subjects with documented auditory neuropathy. Tuning curve width, slope and tip characteristics, as well as rate of suppression growth were measured in each group. Contralateral suppression of otoacoustic emissions (OAEs) was also recorded as an index of medial efferent function. Results show that the four subjects with auditory neuropathy lacked efferent suppression of OAEs. However, these four subjects showed normal estimates of cochlear tuning as measured by DPOAE suppression results. This finding suggests that normal efferent system function is not required at the time of test for normal DPOAE suppression tuning. It also suggests that cochlear function as evaluated by detailed measures of DPOAE suppression, is normal in these "typical" patients with auditory neuropathy.
Highlights
Kummer, P., Janssen, T., & Arnold, W. (1995)
DPOAE generation site, degree of suppression tuning and growth of suppression were found to be normal in these four subjects with auditory neuropathy, providing detailed evidence of normal mechanical processes in the cochleae of these “classic” or typical patients with auditory neuropathy
Considering the fact that the contralateral suppression of OAEs was absent in all four subjects, the DPOAE suppression results can be assumed to exist in the absence of normal efferent influence to the OHCs of the cochlea
Summary
SubjectsFour subjects with auditory neuropathy participated in this study. Table 1 summarizes their ages when first diagnosed with auditory neuropathy and their ages at test. Included are basic test results, such as the acoustic reflex test and ABR, confirming their status as patients with auditory neuropathy. None of the four subjects with auditory neuropathy were found to have any other neurologic dysfunction at the time of test. The 15 normal-hearing young adults used as control subjects are fully described in another report (Abdala, 1998). These subjects had normal audiograms (Ͻ15 dB HL) and a negative history of otologic disease or noise exposure
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