The precedence effect for lateralization for the mild sensory neural hearing impaired

Using dichotic signals presented by headphone, stimulus onset dominance (the precedence effect for lateralization) was investigated for six sensorineural hearing-impaired subjects. Stimuli were based on 2400-Hz lowpass-filtered 5-ms noise bursts. We used the paradigm, as described by Goverts et al. (2000, Hear. Res. 148, 88-94), in which a single noise burst is divided into leading and lagging parts, with opposite lateralization cues (viz. an interaural time delay of 0.2 ms). The occurrence of onset dominance was investigated by measuring the lateral perception of the stimulus ('left' or 'right') with fixed, equal durations of leading and lagging parts, while decreasing the absolute signal level or adding a filtered white noise. The dominance of the leading part was quantified by measuring the lateral perception of the stimulus as a function of the relative duration of the leading (and thus the lagging) part. This was done at about 40 dB sensation level (SL) in quiet and in filtered white noise, at a signal-to-noise ratio resulting in a SL of about 6 dB. Results are compared to normal hearing reference data at various SLs. Hearing-impaired data show a large variance and overall a decreased precedence effect in terms of both occurrence and quantification, which cannot be explained on basis of reduced audibility. Mean performance of the hearing-impaired subjects at 40 dB in quiet was similar to normal hearing performance in masking noise at a signal-to-noise ratio of 0 dB.