Effect of Spectral Channels on Speech Recognition, Comprehension, and Listening Effort in Cochlear-Implant Users

In favorable listening conditions, cochlear-implant (CI) users can reach high speech recognition scores with as little as sevenactive electrodes. Here, we hypothesized that even when speech recognition is high, additional spectral channels may stillbenefit other aspects of speech perception, such as comprehension and listening effort. Twenty-five adult, postlinguallydeafened CI users, selected from two Dutch implant centers for high clinical word identification scores, participated in twoexperiments. Experimental conditions were created by varying the number of active electrodes of the CIs between 7 and 15.In Experiment 1, response times (RTs) on the secondary task in a dual-task paradigm were used as an indirect measure oflistening effort, and in Experiment 2, sentence verification task (SVT) accuracy and RTs were used to measure speechcomprehension and listening effort, respectively. Speech recognition was near ceiling for all conditions tested, as intended bythe design. However, the dual-task paradigm failed to show the hypothesized decrease in RTs with increasing spectralchannels. The SVT did show a systematic improvement in both speech comprehension and response speed across allconditions. In conclusion, the SVT revealed additional benefits in both speech comprehension and listening effort forconditions in which high speech recognition was already achieved. Hence, adding spectral channels may provide benefitsfor CI listeners that may not be reflected by traditional speech tests. The SVT is a relatively simple task that is easy toimplement and may therefore be a good candidate for identifying such additional benefits in research or clinical settings.