Reduced temporal processing in older, normal-hearing listeners evident from electrophysiological responses to shifts in interaural time difference.
Previous electrophysiological studies of interaural time difference (ITD) processing have demonstrated that ITDs are represented by a nontopographic population rate code. Rather than narrow tuning to ITDs, neural channels have broad tuning to ITDs in either the left or right auditory hemifield, and the relative activity between the channels determines the perceived lateralization of the sound. With advancing age, spatial perception weakens and poor temporal processing contributes to declining spatial acuity. At present, it is unclear whether age-related temporal processing deficits are due to poor inhibitory controls in the auditory system or degraded neural synchrony at the periphery. Cortical processing of spatial cues based on a hemifield code are susceptible to potential age-related physiological changes. We consider two distinct predictions of age-related changes to ITD sensitivity: declines in inhibitory mechanisms would lead to increased excitation and medial shifts to rate-azimuth functions, whereas a general reduction in neural synchrony would lead to reduced excitation and shallower slopes in the rate-azimuth function. The current study tested these possibilities by measuring an evoked response to ITD shifts in a narrow-band noise. Results were more in line with the latter outcome, both from measured latencies and amplitudes of the global field potentials and source-localized waveforms in the left and right auditory cortices. The measured responses for older listeners also tended to have reduced asymmetric distribution of activity in response to ITD shifts, which is consistent with other sensory and cognitive processing models of aging.
Department of Communication Sciences and Disorders, University of South Florida, Tampa, Florida eozmeral@usf.edu.
Erol J
0000-0001-9529-001X
EJ
Ozmeral
Department of Communication Sciences and Disorders, University of South Florida, Tampa, Florida.
David A
DA
Eddins
Department of Communication Sciences and Disorders, University of South Florida, Tampa, Florida.
Ann C
AC
Eddins
D000161:Acoustic Stimulation; D000162:Acoustics; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D001303:Auditory Cortex / Q000502:physiology; D001306:Auditory Pathways / Q000502:physiology; D003463:Cues; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011930:Reaction Time / Q000502:physiology*; D013017:Sound Localization / Q000502:physiology*; D013998:Time Perception / Q000502:physiology*; D055815:Young Adult
aging; auditory event-related potentials; auditory temporal processing; binaural hearing; electroencephalography; hemifield code
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