Audiovisual Perception of Sentence Stress in Cochlear Implant Recipients.

Sentence stress as part of linguistic prosody plays an important role for verbal communication. It emphasizes particularly important words in a phrase and is reflected by acoustic cues such as the voice fundamental frequency. However, visual cues, especially facial movements, are also important for sentence stress perception. Since cochlear implant (CI) recipients are limited in their use of acoustic prosody cues, the question arises as to what extent they are able to exploit visual features. Virtual characters were used to provide highly realistic but controllable stimuli for investigating sentence stress in groups of experienced CI recipients and typical-hearing (TH) peers. In addition to the proportion of correctly identified stressed words, task load was assessed via reaction times (RTs) and task-evoked pupil dilation (TEPD), and visual attention was estimated via eye tracking. Experiment 1 considered congruent combinations of auditory and visual cues, while Experiment 2 presented incongruent stimuli. In Experiment 1, CI users and TH participants performed similarly in the congruent audiovisual condition, while the former were better at using visual cues. RTs were generally faster in the AV condition, whereas TEPD revealed a more detailed picture, with TH subjects showing greater pupil dilation in the visual condition. The incongruent stimuli in Experiment 2 showed that modality use varied individually among CI recipients, while TH participants relied primarily on auditory cues. Visual cues are generally useful for perceiving sentence stress. As a group, CI users are better at using facial cues than their TH peers. However, CI users show individual differences in the reliability of the various cues.