Amplitude--intensity functions for auditory middle latency responses in hearing-impaired subjects

Results from animal studies show that hearing loss can result in increased neural responsiveness within the central auditory system. This study employed auditory middle latency evoked responses to compare central auditory responsiveness in human males with and without hearing loss. Measurements of auditory middle latency responses (MLRs) recorded from 14 normal hearing males were compared with MLR measures from 14 males with high-frequency, sensorineural hearing loss. Sixteen toneburst stimuli (four frequencies x four intensities) were used. Slopes of the amplitude-intensity functions for the several components of the MLR were obtained for each subject at frequencies below, near, and above the audiometric edge. Analysis of variance (ANOVA) revealed a significant group effect for MLR component Pa-Na, with less steep slopes at all frequencies for the hearing-impaired group. The ANOVA also showed a trend towards a significant group effect for Pb-Nb. Two-sample t-tests performed for Pb-Nb for each of the four tonebursts showed a frequency-specific effect. For Pb-Nb there was a statistically greater mean slope for the hearing-impaired group at the toneburst frequency associated with the audiometric edge.