Effects of age and hearing loss on gap detection and the precedence effect: broadband stimuli.

Older listeners with normal-hearing sensitivity and impaired-hearing sensitivity often demonstrate poorer-than-normal performance on tasks of speech understanding in noise and reverberation. Deficits in temporal resolution and in the precedence effect may underlie this difficulty. Temporal resolution is often studied by means of a gap-detection paradigm. This task is similar to binaural fusion paradigms used to measure the precedence effect. The purpose of this investigation was to determine if within-channel (measured with monotic and diotic gap detection) or across-channel (measured with dichotic gap detection) temporal resolution is related to fusion (measured with lag-burst thresholds; LBTs) under dichotic, anechoic, and reverberant conditions. Gap-detection thresholds (GDTs) and LBTs were measured by means of noise-burst stimuli for 3 groups of listeners: young adults with normal-hearing sensitivity (YNH), older adults with normal-hearing sensitivity (ONH), and older adults with impaired-hearing sensitivity (OIH). The GDTs indicated that across-channel temporal resolution is poorer than within-channel temporal resolution and that the effects of age and hearing loss are dependent on condition. Results for the fusion task indicated higher LBTs in reverberation than for the dichotic and anechoic conditions, regardless of group, and no effect of age or hearing loss for the nonreverberant conditions. However, higher LBTs were observed in the reverberant condition for the ONH listeners. Further, there was a correlation between across-channel temporal resolution and fusion in reverberation. Gap detection and fusion may not necessarily reflect the same underlying processes; however, across-channel gap detection may influence fusion under certain conditions (i.e., in reverberation).