Differential Effects of Aging and Hearing Loss on Two Speech-Based Binaural Processes: Spectro-Temporal Integration...

Aging and hearing loss may affect the mechanisms underlying binaural speech perception, but whether spectro-temporal integration and interaural cue-based unmasking exhibit shared or dissociable vulnerabilities remains unclear. To isolate these processes, the authors combined two novel, complementary behavioral paradigms: (1) a sparsely coded atomic speech dichotic task designed to minimize spectro-temporal redundancy and probe cross-ear integration of sparse spectro-temporal information, and (2) an antiphasic Chinese Zodiac-in-Noise test that probes binaural unmasking through interaural phase/time cues.

Eighty-six Mandarin-speaking adults were assigned to younger normal hearing, older normal hearing, and older hearing loss (OHL) groups. Experiment 1 used atomic speech stimuli, in which discrete "Gabor atoms" were presented either monaurally or dichotically, and the atom rate reception threshold was defined as the minimum atom rate required for 50% intelligibility. Experiment 2 assessed listeners' ability to exploit interaural timing cues for speech unmasking via the Zodiac-in-Noise test by comparing diotic and antiphasic speech reception thresholds and deriving the binaural intelligibility level difference. Both tasks were repeated across three sessions to evaluate exposure-related changes.

In experiment 1, older adults (older normal hearing and OHL) showed elevated atom rate reception thresholds in both monaural and dichotic conditions relative to younger listeners. Aging, rather than hearing loss, emerged as the primary predictor of reduced binaural spectro-temporal integration after accounting for monaural performance. In experiment 2, absolute speech reception thresholds showed graded effects of both aging and hearing loss, whereas the derived binaural benefit (binaural intelligibility level difference) was reduced primarily in the OHL group. Performance in the two paradigms was uncorrelated. Repeat exposure selectively enhanced binaural spectro-temporal integration in older adults but produced no measurable effect on interaural phase difference (IPD)-based binaural unmasking.

The atomic speech paradigm revealed an age-specific decline in central spectro-temporal integration, whereas IPD-based binaural unmasking was most clearly reduced in older listeners with hearing loss. These findings support a functional dissociation between binaural spectro-temporal and IPD-based processes and highlight the value of sparse atomic speech stimuli for probing central auditory aging and informing age-adaptive rehabilitation strategies.