Phoneme perception via hearing aids with and without compression and the role of temporal resolution

Hearing impairment is more than a sensitivity loss. The causes of reduced discrimination can be found also in deteriorations in loudness perception (recruitment), frequency resolution and temporal resolution. Only recruitment can be compensated for by modern hearing aids, namely by the reduction of the dynamic range by means of compression. However, the introduction of compression introduces temporal distortions, which may deteriorate the temporal cues of speech. In this study the perception of nonsense consonant-vowel-consonant-words presented through hearing aids was studied in a group of 12 hearing-impaired listeners. Phoneme perception in conditions with and without compression was analyzed and related to temporal parameters of the listeners' hearing. A detailed analysis of the patterns of confusions revealed clear qualitative differences in the perception of phonemes with and without compression. These differences can be related to an improved perception of temporal cues like the preburst silent interval of plosives and to spectral changes induced by the activation of the compression circuit. A reduced temporal resolution is disadvantageous for the perception of temporal cues like plosive detection, but our data do not suggest that the perception of temporal cues is hampered excessively by temporal distortions from the compression circuit itself.