Cortical representation of masked speech: effects of age, attention, and linguistic information in maskers

Age-related declines in speech recognition are consistently linked to several interrelated factors - auditory acuity (peripheral and/or central), cognition, linguistic processing, neurophysiological efficiency, etc. These declines become more apparent in adverse listening conditions, such as informational masking, the additional masking effects that occur due to linguistic and/or cognitive confusions between the target sound and masker. In this study, we evaluated the age-related changes in the cortical representation of speech under different masking (informational vs energetic) and attention (active vs passive) conditions. We measured high-density cortical auditory evoked potentials (CAEPs) in 60 participants (30 young adults and 30 older adults) with clinically normal hearing (pure tone average <15 dB HL). CAEPs were recorded in the presence of informational and energetic (no linguistic information) maskers, while the participants either attended (active attention) or ignored (passive attention) the stimuli. Results showed that informational maskers caused significantly greater N1 latency delays than energetic maskers, with older adults showing significantly greater delays than younger adults. Active attention resulted in significantly larger N1 amplitudes compared to passive attention, with minimal age-related differences, possibly due to the strict criteria of auditory acuity in the older adult group. Further, microstate segmentation analyses, in addition to confirming the age-related delays in cortical responses (similar to N1 latencies), revealed longer engagement of fronto-central cortical regions under informational maskers, regardless of the presence of lexical-semantic information in the maskers. These findings, therefore, highlight the systematic effects of aging, attention, and linguistic complexity on the cortical representation of masked speech.