Can age-related decline in speech understanding be explained by peripheral hearing loss?

Speech audiometric scores were compared across the age range from 50 to 90 years in 137 subjects selected in such a way that average audiometric thresholds were matched across four age groups. Thus any age-related changes in speech audiometric scores could not be attributed to age-related differences in peripheral hearing sensitivity. Four speech audiometric measures were studied; phonemically-balanced words (PB), Speech Perception in Noise (SPIN) test for both high- and low-predictability sentences, and the Synthetic Sentence Identification (SSI) test. There was an age trend for all four speech measures but only the change in SSI (30%) was statistically significant. The argument that the change in SSI can be explained by subtle changes in the auditory periphery, not reflected in audiometric thresholds, is weakened by the fact that the change in SSI was greater than the change in either of the two monosyllabic word tests (PB and SPIN-low). The argument that the change in SSI can be explained by concomitant cognitive decline is not supported by correlations among SSI performance and any of several neuropsychological measures of cognitive function in the same subjects. Finally, the lack of a significant interactive effect between hearing sensitivity level and cognitive status does not support a model in which a peripherally degraded speech signal interacts with a deficit in cognitive function to produce the decline in speech audiometric scores. We conclude that the observed age-related decline in SSI performance cannot be satisfactorily explained by peripheral hearing sensitivity loss.