Age-related changes in gap detection thresholds in adult cochlear-implant users: Effects of stimulus level and electrode-to-neural interface

Abstract

Aging is associated with reduced sensitivity to brief temporal gaps in auditory stimuli. Although gap detection is a relative strength among late-deafened cochlear-implant users, aging and electrode-to-neural interface (ENI) factors may contribute to temporal processing difficulties. Because aging may negatively impact perception particularly at very low and very high input levels, we hypothesized larger gap detection thresholds (GDTs) at poor-ENI electrodes and an interaction between age and level such that GDT improvement with increased level would be less evident in older listeners. GDTs were measured on three electrodes selected to span a range of good-to-poor ENI based on electrically-evoked compound action potential amplitude growth or threshold sensitivity to increased pulse rate. GDTs were assessed using constant-amplitude single-electrode 1000-pps pulse trains presented at 40/60/80/100% dynamic range. In preliminary data (N = 4), GDTs averaged 3 ms at 100%DR and 40 ms at 40%DR. Listeners with better average ENI metrics displayed better GDTs. Within-subject, an advantage for best-ENI electrode over poorer-ENI electrodes was evident only at low levels. Finding an interaction between age and level such that temporal processing is impaired at both low and high (but not mid) levels for older listeners may help elucidate the contributions of peripheral versus central factors.