Delayed Stream Segregation in Older Adults

In Brief Objective: To determine whether the time course for the buildup of auditory stream segregation differs between younger and older adults. Design: Word recognition thresholds were determined for the first and last keywords in semantically anomalous but syntactically correct sentences (e.g., “A rose could paint a fish”) when the target sentences were masked by speech-spectrum noise, 3-band vocoded speech, 16-band vocoded speech, intact and colocated speech, and intact and spatially separated speech. A significant reduction in thresholds from the first to the last keyword was interpreted as indicating that stream segregation improved with time. Results: The buildup of stream segregation is slowed for both age groups when the masker is intact, colocated speech. Conclusions: Older adults are more disadvantaged; for them, stream segregation is also slowed even when a speech masker is spatially separated, conveys little meaning (3-band vocoding), and vocal fine structure cues are impoverished but envelope cues remain available (16-band vocoding). Older and younger adults repeated words in nonsense sentences. Speech-spectrum noise was the control masker; there were four comparison two-talker speech maskers (co-located, spatially separated, 3-band and 16-band noise-vocoded). Performance was measured as the 50% correct SNR threshold for sentence-initial and sentence-final keywords. For both age groups, performance improved across keywords when the target and masker were co-located and acoustically similar (intact two-talker speech), but not when the masker was speech-spectrum noise. Unlike younger adults, older adults’ performance also improved with sentence position when the masker was noise-vocoded or spatially separated, indicating age-related slowing in stream segregation in these conditions.