Monaural and binaural time resolution ability in the aged. A psychoacoustic and electrophysiological study

Time resolution ability is an important factor of auditory processing, especially in binaural hearing. In psychoacoustical and electrophysiological studies the time resolution of brief modulations of signal amplitude and frequency in monaural hearing, including gap detection ability, was analysed. To reveal the time resolution ability of the binaural hearing system, brief interaural modulations of signal amplitude, short changes of interaural time delay or noise coherence in broadband noise bursts were generated. The sensation levels of these short-lasting changes in the noise structure and the cortical evoked potentials were investigated in young normal hearing subjects and in the elderly. Thus age-dependent changes in monaural and binaural time resolution ability could be detected. For the monaural experiments, lengthened time constants of between 2-20 ms, depending on the degree of intensity or frequency modulation could be derived for older subjects. The binaural experiments were characterized by prolongation between 4-26 ms for short interaural signal delay changes. For both groups the time constants derived from the electrophysiological investigations were more prolonged, which might be explained by masking effects or habituation. Further electrophysiological investigations will be required to differentiate between time resolution processes of brief signal changes within the peripheral and central parts of the auditory system.