A decline in temporal resolution, or the ability of the auditory system to track fast changes in incoming sounds, is one factor thought to contribute to difficulties in speech perception that accompany the aging process. Aging effects on gap detection abilities, using behavioral or isolated electrophysiologic measures, have been studied previously. However, peripheral and central electrophysiological, and behavioral measures of temporal resolution have not been examined in the same subjects. Also, the relationship between age-related changes in temporal resolution and speech perception is still unclear, as is their interaction with cognition. By revisiting this question in CI users, it was possible to study aging effects on temporal resolution without the potential confound of age-related hearing loss. In addition, the device allows for manipulations of the temporal properties of a signal without concomitant changes in its spectrum, and for auditory-nerve recordings.
This study had two main goals: (1) to determine how aging affects temporal resolution at the auditory periphery, the cortex and perceptually; and (2) to explore the relationship between age-related changes in temporal resolution, general cognitive functioning and speech perception.
Results showed that when the auditory system is stimulated with a cochlear implant, few effects of advancing age on temporal resolution are evident. It is possible that, by stimulating the auditory nerve with precise timing, cochlear implants can help users overcome temporal resolution deficits. Alternatively, and perhaps more likely, it is possible that previous studies that reported age effects on temporal resolution were largely influenced by differences in peripheral processing, which were minimized in this study by the use of a cochlear implant.
Across the age groups, digit span was the only variable significantly correlated with speech perception in noise and perception of time-compressed speech. A longer memory span for digits was associated with better outcomes in both tests of speech perception. This finding is consistent with previous research, and underscores the notion that cognitive factors, not age, may be more important for speech perception.