Temporal Fine-Structure Coding and Lateralized Speech Perception in Normal-Hearing and Hearing-Impaired Listeners.

Area of Science:

• Auditory Neuroscience
• Speech Perception
• Hearing Impairment Research

Background:

• Speech perception in complex auditory scenes is challenging for individuals with hearing impairment (HI).
• The role of temporal fine-structure (TFS) coding in low frequencies for speech understanding in spatialized noise is not fully understood for HI listeners.

Purpose of the Study:

• To investigate the relationship between speech perception in complex spatial listening conditions and TFS coding in young normal-hearing (NH) and elderly HI listeners.
• To determine if TFS coding deficits contribute to speech understanding difficulties in HI listeners within challenging acoustic environments.

Main Methods:

• Speech reception thresholds (SRTs) were measured in various noise conditions (babble, shaped noise) with spatially separated or co-located maskers using interaural time differences.
• Temporal fine-structure (TFS) coding was assessed using frequency discrimination and interaural phase difference (IPD) thresholds at 250 Hz.
• Participants included NH listeners and two groups of elderly HI listeners with mild/moderate loss above 1.5 kHz.

Main Results:

• NH listeners exhibited significantly better SRTs than HI listeners.
• The benefit of spatial separation (binaural unmasking) on SRTs was only slightly reduced in HI listeners compared to NH listeners.
• Neither frequency discrimination nor IPD thresholds correlated with SRTs or binaural unmasking, indicating no link to TFS coding.

Conclusions:

• Elderly HI listeners experience difficulties in spatially complex listening environments, but these are not explained by deficits in low-frequency TFS coding.
• The observed speech understanding limitations in HI listeners are weakly associated with reduced binaural unmasking for spatially separated sounds.
• TFS coding at low frequencies does not appear to be a primary factor limiting speech perception in challenging spatial conditions for HI individuals.