Effortful Listening Despite Correct Responses: The Cost of Mental Repair in Sentence Recognition by Listeners With Cochlear Implants.

PURPOSE: Speech recognition percent correct scores fail to capture the effort of mentally repairing the perception of speech that was initially misheard. This study measured the effort of listening to stimuli specifically designed to elicit mental repair in adults who use cochlear implants (CIs). METHOD: CI listeners heard and repeated sentences in which specific words were distorted or masked by noise but recovered based on later context: a signature of mental repair. Changes in pupil dilation were tracked as an index of effort and time-locked with specific landmarks during perception. RESULTS: Effort significantly increases when a listener needs to repair a misperceived word, even if the verbal response is ultimately correct. Mental repair of words in a sentence was accompanied by greater prevalence of errors elsewhere in the same sentence, suggesting that effort spreads to consume resources across time. The cost of mental repair in CI listeners was essentially the same as that observed in listeners with normal hearing in previous work. CONCLUSIONS: Listening effort as tracked by pupil dilation is better explained by the mental repair and reconstruction of words rather than the appearance of correct or incorrect perception. Linguistic coherence drives effort more heavily than the mere presence of mistakes, highlighting the importance of testing materials that do not constrain coherence by design.

Assessment of Spectral and Temporal Resolution in Cochlear Implant Users Using Psychoacoustic Discrimination and Speech Cue Categorization.

OBJECTIVES: This study was conducted to measure auditory perception by cochlear implant users in the spectral and temporal domains, using tests of either categorization (using speech-based cues) or discrimination (using conventional psychoacoustic tests). The authors hypothesized that traditional nonlinguistic tests assessing spectral and temporal auditory resolution would correspond to speech-based measures assessing specific aspects of phonetic categorization assumed to depend on spectral and temporal auditory resolution. The authors further hypothesized that speech-based categorization performance would ultimately be a superior predictor of speech recognition performance, because of the fundamental nature of speech recognition as categorization. DESIGN: Nineteen cochlear implant listeners and 10 listeners with normal hearing participated in a suite of tasks that included spectral ripple discrimination, temporal modulation detection, and syllable categorization, which was split into a spectral cue-based task (targeting the /ba/-/da/ contrast) and a timing cue-based task (targeting the /b/-/p/ and /d/-/t/ contrasts). Speech sounds were manipulated to contain specific spectral or temporal modulations (formant transitions or voice onset time, respectively) that could be categorized. Categorization responses were quantified using logistic regression to assess perceptual sensitivity to acoustic phonetic cues. Word recognition testing was also conducted for cochlear implant listeners. RESULTS: Cochlear implant users were generally less successful at utilizing both spectral and temporal cues for categorization compared with listeners with normal hearing. For the cochlear implant listener group, spectral ripple discrimination was significantly correlated with the categorization of formant transitions; both were correlated with better word recognition. Temporal modulation detection using 100- and 10-Hz-modulated noise was not correlated either with the cochlear implant subjects' categorization of voice onset time or with word recognition. Word recognition was correlated more closely with categorization of the controlled speech cues than with performance on the psychophysical discrimination tasks. CONCLUSIONS: When evaluating people with cochlear implants, controlled speech-based stimuli are feasible to use in tests of auditory cue categorization, to complement traditional measures of auditory discrimination. Stimuli based on specific speech cues correspond to counterpart nonlinguistic measures of discrimination, but potentially show better correspondence with speech perception more generally. The ubiquity of the spectral (formant transition) and temporal (voice onset time) stimulus dimensions across languages highlights the potential to use this testing approach even in cases where English is not the native language.