Apr 19th 2013 (Fri)
HRC Seminar with Agnes Leger

Dr. Agnes Leger, Postdoctoral Associate, Research Laboratory of Electronics, MIT

Title: Abnormal speech processing for hearing-impaired listeners in frequency regions where absolute thresholds are normal


Speech intelligibility is reduced for listeners with sensorineural hearing loss, especially in noise. The extent to which this reduction is due to reduced audibility or supra-threshold deficits is still debated. The specific influence of supra-threshold deficits on speech intelligibility was investigated.

   The intelligibility of nonsense speech signals in quiet and in various noise maskers was measured for normal-hearing (NH) and hearing-impaired (HI) listeners with hearing loss in high-frequency regions. Participants in both groups had a wide range of ages. The effect of audibility was limited by filtering the signals into low (≤1.5 kHz), mid (1-3 kHz) and low+mid (≤3 kHz) frequency regions, where pure-tone sensitivity was normal or near-normal for the HI listeners. The influence of impaired frequency selectivity on speech intelligibility was investigated for NH listeners by simulating broadening of the auditory filters using a spectral-smearing algorithm. Temporal fine structure sensitivity was estimated for NH and HI listeners by measuring sensitivity to interaural phase differences. Otoacoustic emissions and brainstem electrical responses were measured.

   HI listeners showed mild to severe intelligibility deficits for speech in quiet and in noise. Similar deficits were obtained for steady and fluctuating noises. Simulated reduced frequency selectivity also led to deficits in intelligibility for speech in quiet and in noise, but these were not large enough to explain the deficits found for the HI listeners. The results suggest that speech deficits for the HI listeners may result from suprathreshold auditory deficits caused by outer hair cell damage and by factors associated with aging. The influence of temporal fine structure sensitivity remains unclear.

   These results suggest that speech intelligibility can be strongly influenced by supra-threshold auditory deficits. Audiometric thresholds within the “normal” range (better than 20 dB HL) do not imply normal auditory function.

Seminar Information

Seminars are generally held on Fridays at 10:30 AM in Room 203 of 44 Cummington Street. (Exceptions in time or location will be noted for any talks that are different).