The contribution of amplitude envelope cues to sentence identification in young and aged listeners

Objective: The purpose of this study was to examine the importance of amplitude envelope cues to sentence identification for aged listeners. We also examined the effect of increasing alterations (i.e., compression ratio) and amount of available frequency content (i.e., number of channels) for this population. Design: Thirty-six listeners were classified according to their age (35 or younger versus 65 and older) and hearing status (normal hearing versus hearing impaired). Within each hearing status, mean hearing threshold thresholds for the young and aged listeners were matched as closely as possible through 4 kHz to control for sensitivity differences across age, and all listeners passed a cognitive screening battery. Accuracy of synthetic sentence identification was measured using stimuli processed to restrict spectral information. Performance was measured as a function of age, hearing status, amount of spectral information, and degradation of the amplitude envelope (using fast-acting compression with compression ratios ranging from 1:1 to 5:1). Results: Mean identification scores decreased significantly with increasing age, the presence of hearing loss, the removal of spectral information, and with increasing distortion of the amplitude envelope (i.e., higher compression ratios). There was a consistent performance gap between young and aged listeners, regardless of the magnitude of change to the amplitude envelope. This suggests that some cue other than amplitude envelope variations is inaccessible to the aged listeners. Conclusions: Although aged listeners performed more poorly overall, they did not show greater susceptibility to alterations in amplitude-envelope cues, such as those produced by fast-acting amplitude compression systems. It is therefore unlikely that compression parameters such as attack and release time or compression ratio would need to be differentially programmed for aged listeners. Instead, the data suggest two possibilities: aged listeners have difficulty accessing the fine-structure temporal cues present in speech, and/or performance is degraded by age-related loss of function at a central processing level.