Reaction times of cochlear implant users to a change in electrode or modulation frequency in the presence of a masker.

Abstract

Spatial and temporal selectivity vary substantially between cochlear implant users, resulting in large differences in speech perception. Direct electrode stimulation offers precise control to capture this variability. However, most studies using direct stimulation have not incorporated interfering stimuli, which may not reflect the complex nature of speech and ambient noise. To address this gap, we introduce the Electrode Interaction Reaction Time (ELI-RT) paradigm, which uses amplitude-modulated, interleaved pulses on two closely spaced electrodes at clinical pulse rates. ELI-RT includes two test types: "∆EL", measuring the participants' manual reaction times to a change in stimulated electrode, and "∆MF", measuring reaction times to a modulation frequency change. Both tests include ongoing interference on an adjacent electrode. We also measured speech-in-noise recognition thresholds. We analyzed data from 16 unilateral cochlear implant users and found that ELI-RT could dissociate participant-, electrode-, and test-dependent factors. The effect of the electrode location along the array differed considerably between participants. The ∆EL and ∆MF tests provided partly complementary insights. Reaction times on these tests correlated with speech-in-noise perception, especially for changes that typically yielded shorter reaction times and for electrodes located in the middle of the array. In conclusion, reaction times to changes in the place of stimulation and modulation frequency, in the presence of interference from an adjacent electrode, offer detailed insights into the acuity of information transfer along the cochlear implant electrode array to the central auditory pathways in cochlear implant users.