Abstract
Adult users of cochlear implants (CIs) must perceive, understand, and recall speech from a sharply degraded acoustic input. These real-world demands of speech processing in CI users can be contrasted with current clinical outcome studies that focus almost entirely on intelligibility of phonemes, words, and short sentences. This thesis consists of two experiments. Experiment 1 tested the recall of discourse passages presented to normal (acoustic) hearing young adults, with noise-band vocoding used to simulate the sound of speech via a CI. Effects on recall accuracy when participants could control the rate of speech by self-pacing the input and when passages had higher, inter-word (cloze) predictability were also tested. Patterns of individuals’ self-pacing and a qualitative analysis of participants’ recall in terms of the proportion of main-level propositions versus minor-level propositions recalled were examined. Additionally, the type of passage—whether it was narrative or expository—was a variable of interest. All of this was done to explore potential effects of speech clarity on processing strategies and how they might interact with passage difficulty. A continuous measure of task-related changes in pupil size were obtained as a measure of processing effort and engagement. Experiment 2 was conducted using the same materials and procedures as Experiment 1, but with actual adult CI users rather than the simulation study in Experiment 1. Results show that CI users’ recall was influenced by the same stimulus features but were less likely to show an advantage for the self-pacing conditions. Results are discussed in terms of effort versus task engagement.