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 seven active electrodes. Here, we hypothesized that even when speech recognition is high, additional spectral channels may still benefit other aspects of speech perception, such as comprehension and listening effort. Twenty-five adult, postlingually deafened CI users, selected from two Dutch implant centers for high clinical word identification scores, participated in two experiments. 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 of listening effort, and in Experiment 2, sentence verification task (SVT) accuracy and RTs were used to measure speech comprehension and listening effort, respectively. Speech recognition was near ceiling for all conditions tested, as intended by the design. However, the dual-task paradigm failed to show the hypothesized decrease in RTs with increasing spectral channels. The SVT did show a systematic improvement in both speech comprehension and response speed across all conditions. In conclusion, the SVT revealed additional benefits in both speech comprehension and listening effort for conditions in which high speech recognition was already achieved. Hence, adding spectral channels may provide benefits for CI listeners that may not be reflected by traditional speech tests. The SVT is a relatively simple task that is easy to implement and may therefore be a good candidate for identifying such additional benefits in research or clinical settings.