Simultaneous Measurement of Steady-State and Transient Electrically-Evoked Auditory Change Complex (eACC) Responses and Functional Near-Infrared Spectroscopy (fNIRS) for Understanding Auditory Perception in Cochlear Implant Users

Background

Discrimination abilities in cochlear implant (CI) users can be measured objectively with electrically-evoked auditory change complex (eACC) responses and functional near-infrared spectroscopy (fNIRS). We have previously measured eACC responses for electrode discrimination following CI activation and observed different rates of change over time in the presence and amplitude of the response.

Immediate aim was to determine if simultaneous measurement of eACC for electrode discrimination and fNIRS responses could be conducted. Ultimately, to better understand changes in cortical activity following implant activation.

Methods

Normal-hearing adults were tested. Stimuli were fifteen 16-second pure-tone sequences, presented in three conditions. In a continuous condition, a 16-second pure tone with a fundamental frequency (F0) of 220 Hz was presented. In a “rapid” switching condition (2.5 Hz), two pure tones (F01= 220 Hz; F02 = 580 Hz) were presented successively. In a “slow” switching condition (1 Hz), tones with the same F0s (as rapid switching) were presented successively.

We observed steady-state and transient electroencephalography responses to better understand neural processing at different levels of the auditory pathway as well as fNIRS to identify maximal brain response regions.

Results

Results suggest that although responses were larger in the “slow” switching condition, both steady-state and transient responses could be elicited with both switching conditions and associated fNIRS responses recorded.

Conclusions

An objective measure paradigm to simultaneously record multiple responses to the same stimuli has been devised. Work is ongoing to optimise the parametrical values of F0 and switching rate. Preliminary results with CI users will be presented.