LOUDNESS PERCEPTION AND FREQUENCY DISCRIMINATION IN SUBJECTS WITH STEEPLY SLOPING HEARING-LOSS - POSSIBLE CORRELATES OF NEURAL PLASTICITY

Loudness functions and frequency difference limens (DLFs) were measure d in five subjects with steeply sloping high-frequency sensorineural h earing loss. The stimuli were pulsed pure tones encompassing a range o f frequencies. Loudness data were obtained using a 2AFC matching proce dure with a 500-Hz reference presented at a number of levels. DLFs wer e measured using a 3AFC procedure with intensities randomized within 6 dB around an equal-loudness level. Results showed significantly shall ower loudness functions near the cutoff frequency of the loss than at a lower frequency, where hearing thresholds were near normal. DLFs wer e elevated, on average, relative to DLFs measured using the same proce dure in five normally hearing subjects, but showed a local reduction n ear the cutoff frequency in most subjects with high-frequency loss. Th e loudness data are generally consistent with recent models that descr ibe loudness perception in terms of peripheral excitation patterns tha t are presumably restricted by a steeply sloping hearing loss. However , the DLF data are interpreted with reference to animal experiments th at have shown reorganization in the auditory cortex following the intr oduction of restricted cochlear lesions. Such reorganization results i n an increase in the spatial representation of lesion-edge frequencies , and is comparable with the functional reorganization observed in ani mals following frequency-discrimination training. It is suggested that similar effects may occur in humans with steeply sloping high-frequen cy hearing loss, and therefore, the local reduction in DLFs in our dat a may reflect neural plasticity. (C) 1998 Acoustical Society of Americ a. [S0001-4966(98)02910-5].