Comparison of Temporal and Envelope Cues in Hearing Aids: Use of Malayalam Language Chimeric Sentences and Two Compression Strategies

Abstract

Objective: The human auditory system perceives any speech sound through the inherent temporal cues i.e., the temporal fine structure (TFS) and envelope (ENV) cues which has its own predominance for perception across languages. Research in English and Mandarin Chinese language showed the difference between these cues with tonal language employ more of TFS cues and non-tonal language employ ENV cues for perception. Earlier studies on Indian language (Kannada and Malayalam) revealed ENV cues predominance for perception. Based on this, the aim of this study was to compare stimuli in which the TFS and ENV cues had been interchanged (so-called auditory chimeras). The stimuli were Malayalam language sentences delivered through a hearing aid using two compression schemes -syllabic compression and dual compression -and processed by a nonlinear 8-channel and 16-channel system.Method: Thirty-five normal hearing individuals were assessed for the perception of chimeric sentences across eight sets of frequency bands (1, 4, 6, 8, 16, 24, 32, and 64 bands). Before the administration of the chimeric sentences all the individuals were assessed for normal hearing abilities through routine audiological evaluations. Results:The results of the present study reveal there is a significant difference across frequency bands on both the syllabic and dual compression processed stimuli using either 8 or 16 channels. The ENV cues were better perceived whether 4, 6, 8, or 16 frequency bands were used, with dual compression being marginally better than syllabic compression for both 8 and 16 channels. However, 16 channels gave overall better perception than 8 channels. Conclusions:The results of the study revealed a better processing of envelope (ENV) cues, which are most important for understanding speech through a hearing aid.