Age effects in discrimination of intervals within accented tone sequences differing in accent type and sequence presentation rate.

The study measured listener sensitivity to increments in the duration of one or two target silent intervals embedded within unaccented tone sequences and sequences that featured a single accented component. The baseline unaccented sequences consisted of six 1000-Hz 40-ms tone bursts that were separated equally by silent intervals to establish a slower tone sequence rate, with tonal inter-onset intervals (IOIs) set to 200 ms, or a faster rate with tonal IOIs set to 100 ms. Stimulus accent was created by doubling the baseline duration of a single sequence component, either the second tone burst (tonal accent), or the second tonal IOI (interval accent). Duration difference limens for increments of the target interval(s) were measured adaptively by varying a single inter-tone silent interval or co-varying two successive inter-tone silent intervals; target intervals occurred at the third, or third and fourth, sequence locations. Listeners included younger normal-hearing adults and groups of older listeners with and without hearing loss. Discrimination for the two older groups was equivalent and poorer than that of the younger listeners, especially for the faster accented sequences. Discrimination was best for stimuli with two successive target intervals, indicating that target repetition within accented sequences acts to improve listener temporal sensitivity.