The influence of stimulation levels on auditory thresholds and speech recognition in adult cochlear implant users

Objective: This study aims to evaluate the influence of minimum and maximum stimulation levels on auditory thresholds and speech recognition abilities in adult cochlear implant users. Method: Fifteen adults implanted with a Cochlear® device with over 12 months listening experience. Participants underwent routine programming for optimization of minimum (T) and maximum comfort (C) stimulation levels, which was saved in Program 1 (MO). Three further maps were constructed artificially adjusting the measured levels: Program 2 - MO with 10 fewer electrical current units at C level (MC-); Program 3 - MO with 10 fewer electric current units at T level (MT-); and Program 4 - MO with 10 more electric current units at T level (MT+). Sound field thresholds, recorded sentence recognition and monosyllable tests were presented in quiet and in noise. Results: There were significantly better thresholds at 1, 3, 4, and 6 kHz frequencies in MT+ and worse in MC-. A statistically significant difference was observed for sentences in quiet and monosyllables in quiet and noise with changing C levels, with worsening of the results for MC- program. Conclusion: The results suggest that T levels above the behavioural threshold provided an improvement in sound field thresholds but did not influence performance on speech recognition tests in quiet and in noise. In contrast, C levels below the behavioural comfort level worsened sound field thresholds and led to poorer performance in tests of sentence recognition in quiet and monosyllable recognition in quiet and in noise.