Effects of auditory rehabilitation on DLF performance.

The experimental design used in the present study was the same as McDermott et al.’s (1998) and Thai Van et al.’s (2003). These studies revealed that DLFs measured near the hearing-loss cut-off frequency in subjects with steeply sloping hearing loss are locally improved, suggesting a central reorganization induced by the hearing loss. Our study is in agreement with these results. DLF scores were significantly better at the initial best frequency (bDLF) than at bDLF+1/8 octave. Furthermore, following auditory rehabilitation, an alteration in DLF scores was observed at the bDLF of each subject, whereas no significant difference was found at any other frequencies. At bDLF, the DLFs that were found to be smallest before rehabilitation were somewhat normalized with respect to other frequencies one month and three months after fitting. The fact that no significant difference could be observed between ‘before’ and ‘6 months after the rehabilitation’ may perhaps be explained by a new phase of plasticity but more probably by procedural or task learning: i.e., subjects progressively improved their DLF performance by doing the test at every frequency including the bDLF. Moreover, these results can certainly not be imputed to an ‘acclimatization effect’ (cognitive changes linked to the hearing-aid fitting) since they were observable only at one single frequency (bDLF) and not at neighbouring frequencies.

During rehabilitation, no change in hearing threshold or loudness perception was observed for the frequencies centred on the bDLF; consequently these two parameters presumably did not influence the change in DLF.