Age-related rollover for spectrally degraded temporal speech contrasts

Abstract

Some speech sounds, or phonemes, are primarily distinguished acoustically from other phonemes by temporal cues. A decline in temporal-processing abilities is a common consequence of aging that might cause a listener to have difficulty differentiating between sounds, especially when the speech is degraded. One type of signal degradation occurs in a cochlear-implant vocoder simulation, which eliminates most of the spectral information in speech while maintaining the temporal envelope. In addition, temporal processing abilities may be challenged at higher presentation levels causing a decrease in performance (i.e., rollover), particularly in older listeners. This study measures the phoneme classification of younger and older listeners of four spectro-temporal contrasts when presented in quiet with and without vocoding at a range of presentation levels. We hypothesized that, due to declines in temporal processing abilities, older listeners would be more susceptible to rollover, measured by a decrease in phoneme classification performance for degraded temporal contrasts as presentation levels increase. We further hypothesized that performance rollover would occur more often for vocoded speech than for unprocessed speech, especially in older listeners. Preliminary data show interactions between speech contrasts, presentation levels, and vocoding. Our results will help facilitate understanding speech perception difficulties in older cochlear-implant users.