Speech understanding and aging: Contributions of peripheral and central mechanisms

The purpose of this investigation was to examine the relative contributions of peripheral and central mechanisms to the age-related communication deficits often described for aging subjects. To accomplish this purpose, peripheral auditory dysfunction consisting of either deficient temporal analysis ability or elevation of peripheral distortion as defined by Plomp (1978) was measured in 17 aging hearing impaired adults and a reference group of eight young normal listeners. In addition, relationships among measures of peripheral auditory dysfunction and the measure of central auditory dysfunction (PB-SSI discrepancy) proposed by Jerger and Hayes (1977) was investigated. Central aging effects as defined by PB-SSI discrepancies were observed in 47.05% of the aging hearing impaired individuals. The aging hearing impaired subjects displayed elevated speech reception thresholds in quiet and required a more advantageous signal-to-noise ratio for speech understanding in high noise conditions. Speech reception thresholds in quiet and low level of background noise were found to be highly dependent on low frequency hearing sensitivity. Speech reception thresholds in moderate and high noise levels were closely related to hearing sensitivity at 4000 Hz. The signal-to-noise ratio model for speech reception threshold proposed by Plomp (1986) was successfully implemented and verified using low predictability stimulus items of the Speech Perception in Noise (SPIN) Test. The attenuation and distortion parameter values obtained in the present investigation for the aging hearing impaired listeners agreed well with previous reports when stimulus and task difficulty is taken into consideration. In general, the aging hearing impaired subjects demonstrated temporal resolution ability within normal limits at 500 Hz and reduced temporal resolution at 4000 Hz. Temporal resolution factors (TRF\u27s) were found to be relatively independent of hearing threshold level at both 500 Hz and 4000 Hz. Information gleaned from the analyses conducted in the present examination, particularly from the principal component analyses, must be considered preliminary and interpreted with extreme caution due to the low subject-to-variable ratio. Future investigations should include a substantial increase in the number of subjects as well as a wider range of speech perception abilities