Triphasic pulse stimulation and evaluation of the spectral - temporal resolution in cochlear implant users

Due to the limitations of the technologies used in cochlear implants (CI), the spectral and temporal cues in auditory stimuli can only be represented to a limited extent. The aim of this study is to evaluate the short-term effects of triphasic pulse (TPP) stimulation, a newly developed stimulation mode, on spectral and temporal resolution abilities in CI users with normal inner ear structures and no facial nerve stimulation. Twenty-one experienced CI users (13 females and 8 males) aged 16-40 years with normal inner ear structures without facial nerve stimulation were included in the study. In order to make the evaluation, a program with TPP stimulation was created based on the feedback of the participants and a 1-hour trial period was given to the participants to gain familiarity with the program. First, the participants were evaluated for hearing thresholds with cochlear implants in the free field with both stimulation modes. Afterwards, Spectral – Temporally Modulated Ripple Test (SMRT), and Modulation Depth Treshold Test (EasyMDT) were conducted. Each participant was evaluated with both the biphasic stimulation mode and the TPP stimulation, and the results obtained in the stimulation modes were compared. As a result of the study, there was no statistically significant difference in spectral resolution skills between TPP and biphasic pulse in short-term use (p>0,05), while significant results were obtained in temporal resolution skills in TPP (p<0,05).When the programming parameters that could affect the findings were compared in both stimulation modes, there was no significant difference between the stimulation modes in the parameters of most comfortable levels, threshold levesl and electrical dynamic ranges (p>0.05), while the stimulus rate and pulse width difference were obtained (p<0,05). As a result, it was inferred that the decrease in current spread due to the structure of the TPP, as well as the rate and duration effect, may be effective in obtaining better results with the TPP in temporal resolution skills. Keywords: Cochlear implant, spectral resolution, temporal resolution, channel interaction, triphasic pulse stimulation