Visual Temporal Acuity Is Related to Auditory Speech Perception Abilities in Cochlear Implant Users

Association of Aging and Cognition With Complex Speech Understanding in Cochlear-Implanted Adults: Use of a Modified National Institutes of Health (NIH) Toolbox Cognitive Assessment

Importance

The association between cognitive function and outcomes in cochlear implant (CI) users is not completely understood, partly because some cognitive tests are confounded by auditory status. It is important to determine appropriate cognitive tests to use in a cohort of CI recipients.

Objective

To provide proof-of-concept for using an adapted version of the National Institutes of Health (NIH) Toolbox Cognition Battery in a cohort of patients with CIs and to explore how hearing in noise with a CI is affected by cognitive status using the adapted test.

Design, Setting, and Participants

In this prognostic study, participants listened to sentences presented in a speech-shaped background noise. Cognitive tests consisted of 7 subtests of the NIH Toolbox Cognition Battery that were adapted for hearing impaired individuals by including written instructions and visual stimuli. Participants were prospectively recruited from and evaluated at a tertiary medical center. All participants had at least 6 months' experience with their CI.

Main Outcomes and Measures

The main outcomes were performance on the adapted cognitive test and a speech recognition in noise task.

Results

Participants were 20 adult perilingually or postlingually deafened CI users (50% male participants; median [range] age, 66 [26-80] years old). Performance on a sentence recognition in noise task was negatively associated with the chronological age of the listener (R2 = 0.29; β = 0.16; standard error, SE = 0.06; t = 2.63; 95% confidence interval, 0.03-0.27). Testing using the adapted version of the NIH Toolbox Cognition Battery revealed that a test of processing speed was also associated with performance, using a standardized score that accounted for contributions of other demographic factors (R2 = 0.28; 95% confidence interval, -0.42 to -0.05).

Conclusions and Relevance

In this prognostic study, older CI users showed poorer performance on a sentence-in-noise test compared with younger users. This poorer performance was correlated with a cognitive deficit in processing speed when cognitive function was assessed using a test battery adapted for participants with hearing loss. These results provide initial proof-of-concept results for using a standardized and adapted cognitive test battery in CI recipients.

Multisensory Integration as a Window into Orderly and Disrupted Cognition and Communication

During our everyday lives, we are confronted with a vast amount of information from several sensory modalities. This multisensory information needs to be appropriately integrated for us to effectively engage with and learn from our world. Research carried out over the last half century has provided new insights into the way such multisensory processing improves human performance and perception; the neurophysiological foundations of multisensory function; the time course for its development; how multisensory abilities differ in clinical populations; and, most recently, the links between multisensory processing and cognitive abilities. This review summarizes the extant literature on multisensory function in typical and atypical circumstances, discusses the implications of the work carried out to date for theory and research, and points toward next steps for advancing the field.

Audiovisual Temporal Processing in Postlingually Deafened Adults with Cochlear Implants

For many cochlear implant (CI) users, visual cues are vitally important for interpreting the impoverished auditory speech information that an implant conveys. Although the temporal relationship between auditory and visual stimuli is crucial for how this information is integrated, audiovisual temporal processing in CI users is poorly understood. In this study, we tested unisensory (auditory alone, visual alone) and multisensory (audiovisual) temporal processing in postlingually deafened CI users (n = 48) and normal-hearing controls (n = 54) using simultaneity judgment (SJ) and temporal order judgment (TOJ) tasks. We varied the timing onsets between the auditory and visual components of either a syllable/viseme or a simple flash/beep pairing, and participants indicated either which stimulus appeared first (TOJ) or if the pair occurred simultaneously (SJ). Results indicate that temporal binding windows-the interval within which stimuli are likely to be perceptually 'bound'-are not significantly different between groups for either speech or non-speech stimuli. However, the point of subjective simultaneity for speech was less visually leading in CI users, who interestingly, also had improved visual-only TOJ thresholds. Further signal detection analysis suggests that this SJ shift may be due to greater visual bias within the CI group, perhaps reflecting heightened attentional allocation to visual cues.

Relationship between vestibular sensitivity and multisensory temporal integration

A single event can generate asynchronous sensory cues due to variable encoding, transmission, and processing delays. To be interpreted as being associated in time, these cues must occur within a limited time window, referred to as a "temporal binding window" (TBW). We investigated the hypothesis that vestibular deficits could disrupt temporal visual-vestibular integration by determining the relationships between vestibular threshold and TBW in participants with normal vestibular function and with vestibular hypofunction. Vestibular perceptual thresholds to yaw rotation were characterized and compared with the TBWs obtained from participants who judged whether a suprathreshold rotation occurred before or after a brief visual stimulus. Vestibular thresholds ranged from 0.7 to 16.5 deg/s and TBWs ranged from 13.8 to 395 ms. Among all participants, TBW and vestibular thresholds were well correlated ( R² = 0.674, P < 0.001), with vestibular-deficient patients having higher thresholds and wider TBWs. Participants reported that the rotation onset needed to lead the light flash by an average of 80 ms for the visual and vestibular cues to be perceived as occurring simultaneously. The wide TBWs in vestibular-deficient participants compared with normal functioning participants indicate that peripheral sensory loss can lead to abnormal multisensory integration. A reduced ability to temporally combine sensory cues appropriately may provide a novel explanation for some symptoms reported by patients with vestibular deficits. Even among normal functioning participants, a high correlation between TBW and vestibular thresholds was observed, suggesting that these perceptual measurements are sensitive to small differences in vestibular function. NEW & NOTEWORTHY While spatial visual-vestibular integration has been well characterized, the temporal integration of these cues is not well understood. The relationship between sensitivity to whole body rotation and duration of the temporal window of visual-vestibular integration was examined using psychophysical techniques. These parameters were highly correlated for those with normal vestibular function and for patients with vestibular hypofunction. Reduced temporal integration performance in patients with vestibular hypofunction may explain some symptoms associated with vestibular loss.

Multisensory Integration in Cochlear Implant Recipients

Speech perception is inherently a multisensory process involving integration of auditory and visual cues. Multisensory integration in cochlear implant (CI) recipients is a unique circumstance in that the integration occurs after auditory deprivation and the provision of hearing via the CI. Despite the clear importance of multisensory cues for perception, in general, and for speech intelligibility, specifically, the topic of multisensory perceptual benefits in CI users has only recently begun to emerge as an area of inquiry. We review the research that has been conducted on multisensory integration in CI users to date and suggest a number of areas needing further research. The overall pattern of results indicates that many CI recipients show at least some perceptual gain that can be attributable to multisensory integration. The extent of this gain, however, varies based on a number of factors, including age of implantation and specific task being assessed (e.g., stimulus detection, phoneme perception, word recognition). Although both children and adults with CIs obtain audiovisual benefits for phoneme, word, and sentence stimuli, neither group shows demonstrable gain for suprasegmental feature perception. Additionally, only early-implanted children and the highest performing adults obtain audiovisual integration benefits similar to individuals with normal hearing. Increasing age of implantation in children is associated with poorer gains resultant from audiovisual integration, suggesting a sensitive period in development for the brain networks that subserve these integrative functions, as well as length of auditory experience. This finding highlights the need for early detection of and intervention for hearing loss, not only in terms of auditory perception, but also in terms of the behavioral and perceptual benefits of audiovisual processing. Importantly, patterns of auditory, visual, and audiovisual responses suggest that underlying integrative processes may be fundamentally different between CI users and typical-hearing listeners. Future research, particularly in low-level processing tasks such as signal detection will help to further assess mechanisms of multisensory integration for individuals with hearing loss, both with and without CIs.