CENTRALAUDITORY PROCESSINGIN AGING: THE DICHOTIC LISTENING PARADIGM

Objective: Aging is associated with cognitive changing. Central auditory processing dysfunction may explain some understanding difficulties in elderly. It may be evaluated with the dichotic listening (DL) test, a widely-used experimental paradigm for studying inter-hemispheric interactions and attentional processes. This study examines central auditory language processing with a dichotic listening task in right-handed old subjects according to their age. Design : Cross sectional-study. Setting : memory clinic and geriatric unit. Participants: Adult group (Ad) consisted in 26 subjects (21 women and 5 men) aged 50-69 years and an old adults group (Old-Ad) consisted in 20 subjects (19 women and 1 man) aged 70 to 89 years. Measurements: DL consisted in a free-recall word task and a digit forced-attention task (forced-right: FR and forced-left: FL) in order to study central auditory language processing. In addition, we used neuropsychological tests to study executive functions and cognitive control, sustained by the prefrontal cortex. Results: In the free recall condition, we confirmed the classic right ear advantage (REA) in both groups, particularly in older subjects. In the forced condition, we observed an ear advantage with a change in ear asymmetry as a consequence of instruction: REA in FR and a left-ear advantage (LEA) in FL. We compared contaminations by the contra-lateral inattentive ear: reports of the left ear (LE) in the FR condition and reports of the right ear (RE) in the FL condition. Contaminations by the RE in the FL condition were more pronounced in Old-Ad suggesting difficulties in competition between the natural tendency for the RE and the instruction. In the Old-Ad group, the correlation between the RE score in FL and TMT B-A/A suggests an impairment in mental flexibility. Conclusion: DL may be helpful to study central auditory dysfunction in aging. Our results suggest difficulties in attentional control and executive functions. Central auditory dysfunction should be evaluated in elderly because it potentially contributes to difficulty of hearing in noisy environment with consequences in the rehabilitation of presbyacousic subjects. More studies are needed to investigate the predictive value of DL as a marker of cognitive decline, particularly executive functions.