Abstract
The acoustic reflex test is an important tool for identifying auditory disorder from the middle ear to the superior olivary complex. Absence of acoustic reflexes is the early sign of many auditory disorders. Absence of acoustic reflex with normal hearing sensitivity may be an early sign of auditory neuropathy with poor encoding of speech at initial stage. Speech auditory brainstem response was recorded with /da/ (40 ms) stimuli in two groups of patients. The control group contained normal-hearing participants with presence of acoustic reflex, whereas the experimental group contained normal-hearing participants with absent acoustic reflexes. The peak latency, amplitude, and F0 and F1 mean amplitude were analyzed in both groups. MANOVA showed no significant difference in any parameter between the control and experimental group. Results of the current study showed that absence of acoustic reflexes in normal-hearing patients without auditory complaint is not sufficient by itself to diagnose the existence of auditory neuropathy. This study also highlighted that normal-hearing patients with absence of acoustic reflex have similar brainstem encoding of speech as that of patients with acoustic reflex.
Highlights
Loud sounds cause involuntary contraction of the stapedius muscle, called acoustic reflex
In clinical practice we see patients without auditory complaints and with hearing threshold within the normal limit correlating with speech audiometry showing absent acoustic reflex responses at values above those expected on an A-type tympanogram
Results of the current study showed no significant difference between control and experimental groups in terms of the latency and amplitude measures of speech auditory brainstem response (ABR)
Summary
Loud sounds cause involuntary contraction of the stapedius muscle, called acoustic reflex. In clinical practice we see patients without auditory complaints and with hearing threshold within the normal limit correlating with speech audiometry showing absent acoustic reflex responses at values above those expected on an A-type tympanogram. A study by Pinotti et al [12] showed that 10% of normal-hearing individuals had absent acoustic reflex, without any ear complaints These findings wherein absence of acoustic reflex occurs alone, with normal pure tone audiometry and speech audiometry, normal tympanometry, and presence of otoacoustic emission within normal patterns have aroused interest in research in these areas. Speech ABR in patients with no auditory complaints, with normal hearing, and with an A-type tympanogram with the absence of acoustic reflex has not been documented yet Such a study would give insight into the processing capability of speech sound in patients with auditory neuropathy.
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