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There is a high degree of variability in speech intelligibility outcomes across cochlear-implant (CI) users. To better understand how auditory cognition affects speech intelligibility with the CI, we performed an electroencephalography study in which we examined the relationship between central auditory processing, cognitive abilities, and speech intelligibility. Postlingually deafened CI users (N=13) and matched normal-hearing (NH) listeners (N=13) performed an oddball task with words presented in different background conditions (quiet, stationary noise, modulated noise). Participants had to categorize words as living (targets) or non-living entities (standards). We also assessed participants' working memory (WM) capacity and verbal abilities. For the oddball task, we found lower hit rates and prolonged response times in CI users when compared with NH listeners. Noise-related prolongation of the N1 amplitude was found for all participants. Further, we observed group-specific modulation effects of event-related potentials (ERPs) as a function of background noise. While NH listeners showed stronger noise-related modulation of the N1 latency, CI users revealed enhanced modulation effects of the N2/N4 latency. In general, higher-order processing (N2/N4, P3) was prolonged in CI users in all background conditions when compared with NH listeners. Longer N2/N4 latency in CI users suggests that these individuals have difficulties to map acoustic-phonetic features to lexical representations. These difficulties seem to be increased for speech-in-noise conditions when compared with speech in quiet background. Correlation analyses showed that shorter ERP latencies were related to enhanced speech intelligibility (N1, N2/N4), better lexical fluency (N1), and lower ratings of listening effort (N2/N4) in CI users. In sum, our findings suggest that CI users and NH listeners differ with regards to both the sensory and the higher-order processing of speech in quiet as well as in noisy background conditions. Our results also revealed that verbal abilities are related to speech processing and speech intelligibility in CI users, confirming the view that auditory cognition plays an important role for CI outcome. We conclude that differences in auditory-cognitive processing contribute to the variability in speech performance outcomes observed in CI users. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Hannover, Finke.Mareike@mh-hannover.de AbstractThere is a high degree of variability in speech intelligibility outcomes across cochlear-implant (CI) users. To better understand how auditory cognition aff...

Objectives: Actively following a conversation can be demanding and limited cognitive resources must be allocated to the processing of speech, retaining and encoding the perceived content, and preparing an answer. The aim of the present study was to disentangle the allocation of effort into the effort required for listening (listening effort) and the effort required for retention (memory effort) by means of pupil dilation. Design: Twenty-five normal-hearing German speaking participants underwent a sentence final word identification and recall test, while pupillometry was conducted. The participants’ task was to listen to a sentence in four-talker babble background noise and to repeat the final word afterward. At the end of a list of sentences, they were asked to recall as many of the final words as possible. Pupil dilation was recorded during different list lengths (three sentences versus six sentences) and varying memory load (recall versus no recall). Additionally, the effect of a noise reduction algorithm on performance, listening effort, and memory effort was evaluated. Results: We analyzed pupil dilation both before each sentence (sentence baseline) as well as the dilation in response to each sentence relative to the sentence baseline (sentence dilation). The pupillometry data indicated a steeper increase of sentence baseline under recall compared to no recall, suggesting higher memory effort due to memory processing. This increase in sentence baseline was most prominent toward the end of the longer lists, that is, during the second half of six sentences. Without a recall task, sentence baseline declined over the course of the list. Noise reduction appeared to have a significant influence on effort allocation for listening, which was reflected in generally decreased sentence dilation. Conclusion: Our results showed that recording pupil dilation in a speech identification and recall task provides valuable insights beyond behavioral performance. It is a suitable tool to disentangle the allocation of effort to listening versus memorizing speech.

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