Fine-grain Study: initial results

Purpose of the study: Auditory percept resulting from stimulation with continuous intensity growth (“fine-grain”) at single stimulation electrodes was analysed. Starting from 0 qu up to the loudest acceptable presentation level (LAPL), stimulation intensity was continuously increased with 1 qu per second (1qu~nano Coulomb). Stimuli were presented in three runs: two continuous growth stimulations at rates of 40 and 80Hz, as well as a growth using larger steps (~1-1.5qu).During the delivery of the stimuli, the threshold of electrical elicitation of the stapedius reflex (eSRT) was monitored and the evoked compound action potentials (ECAPs) were recorded. Materials and Methods used: In earlier analysis of the continuous stimulation growth with larger with different charge steps (44Hz vs 80Hz) a difference in LAPL was observed: Lutz et al [2015] showed that the LAPL was considerably smaller for larger charges steps (at 44Hz) compared to 80Hz (~18qu versus ~21qu respectively ). It remained unsolved whether the stimulation frequency and/or the step size are influencing factors. Additionally it was not investigated if the stapedius reflex is influenced by the varying stimuli. Continuous growth stimuli were presented on all stimulating electrodes; and non-continuous stimuli were presented on three representative electrodes in the apical / middle / basal region. Recordings were performed on n=12 cooperative pediatric cochlear implant recipients aged 6 to 10 years at the Audiology Dept. of the University of Milano. Results: Determination of ECAP parameters (threshold and amplitude growth with respect to the stimulation intensity) was considerably faster using the fine-grain stimuli (compare to Lutz et al.). Identification of neural responses was easier for the fine-grain stimuli due to the higher resolution of stimulation intensities. The eSRT varied according to the different LAPLs reached;the analysis of the correlation is done regarding of the correlation between eSRT and LAPL for the different stimuli is presented. Conclusion: Information about the obtained loudest acceptable presentation limit and the elicitation of the eSRT stapedius reflex provide further insights about the nature of the electrically evoked auditory percept in children. Our results support the use of objective measures such as the variation of stimulation intensity and continuous growth to assess the change in auditory percept . Besides these findings, our study confirmed the suitability of the fine-grain stimulation paradigm for a paediatric population. References: Lutz et al [2015] Conference on Implantable Auditory Prostheses: Influence of the Recording Electrode on the ECAP Threshold using a Novel fine-grain Recording Paradigm.