Semantic influences on the perception of degraded speech by individuals with cochlear implants

This study investigated whether speech intelligibility in cochlear implant (CI) users is affected by semantic context. Three groups participated in two experiments: Two groups of listeners with normal hearing (NH) listened to either full spectrum speech or vocoded speech, and one CI group listened to full spectrum speech. Experiment 1 measured participants' sentence recognition as a function of target-to-masker ratio (four-talker babble masker), and experiment 2 measured perception of interrupted speech as a function of duty cycles (long/short uninterrupted speech). Listeners were presented with both semantic congruent/incongruent targets. Results from the two experiments suggested that NH listeners benefitted more from the semantic cues as the listening conditions became more challenging (lower signal-to-noise ratios and interrupted speech with longer silent intervals). However, the CI group received minimal benefit from context, and therefore performed poorly in such conditions. On the contrary, in the conditions that were less challenging, CI users benefitted greatly from the semantic context, and NH listeners did not rely on such cues. The results also confirmed that such differential use of semantic cues appears to originate from the spectro-temporal degradations experienced by CI users, which could be a contributing factor for their poor performance in suboptimal environments.