Olivier Deguine

McGurk effects in cochlear-implanted deaf subjects.

Cochlear implants are neuroprostheses designed to restore speech perception in case of profound bilateral hearing loss. As speech is fundamentally an audiovisual percept, a deficit in processing auditory information might lead to changes in audiovisual integration of speech comprehension. Using vowel-consonant-vowel stimuli under unimodal, audiovisual congruent and audiovisual incongruent (McGurk) conditions, we tested postlingually deaf cochlear-implanted (CI) users and normally hearing (NH) subjects in order to investigate their audiovisual perceptive strategies. Mode/Place-of-articulation perceptive analysis and information transmission analysis of congruent and incongruent percepts indicated a similar sensory specialization for CI users when compared to NH subjects, with voicing and nasality cues transmitted via audition and place cues principally transmitted via vision. NH as well as CI subjects underwent typical McGurk illusory percepts. However, while normally hearing subjects show a well-balanced bimodal integration of incongruent speech, we demonstrated that cochlear implantees present a bias toward a visual-predominant bimodal integration. Our results are complementary to previous studies showing that CI users maintain a high level of speechreading, even after several years of recovery of auditory speech comprehension. Altogether, our results suggest a cross-modal reorganization of speech comprehension in cochlear-implanted patients that might recruit more strongly than in NH the visual and visuo-auditory brain areas involved in speechreading.

Evolution of crossmodal reorganization of the voice area in cochlear-implanted deaf patients†

Psychophysical and neuroimaging studies in both animal and human subjects have clearly demonstrated that cortical plasticity following sensory deprivation leads to a brain functional reorganization that favors the spared modalities. In postlingually deaf patients, the use of a cochlear implant (CI) allows a recovery of the auditory function, which will probably counteract the cortical crossmodal reorganization induced by hearing loss. To study the dynamics of such reversed crossmodal plasticity, we designed a longitudinal neuroimaging study involving the follow‐up of 10 postlingually deaf adult CI users engaged in a visual speechreading task. While speechreading activates Brocas area in normally hearing subjects (NHS), the activity level elicited in this region in CI patients is abnormally low and increases progressively with post‐implantation time. Furthermore, speechreading in CI patients induces abnormal crossmodal activations in right anterior regions of the superior temporal cortex normally devoted to processing human voice stimuli (temporal voice‐sensitive areas‐TVA). These abnormal activity levels diminish with post‐implantation time and tend towards the levels observed in NHS. First, our study revealed that the neuroplasticity after cochlear implantation involves not only auditory but also visual and audiovisual speech processing networks. Second, our results suggest that during deafness, the functional links between cortical regions specialized in face and voice processing are reallocated to support speech‐related visual processing through cross‐modal reorganization. Such reorganization allows a more efficient audiovisual integration of speech after cochlear implantation. These compensatory sensory strategies are later completed by the progressive restoration of the visuo‐audio‐motor speech processing loop, including Brocas area. Hum Brain Mapp, 2012.

Visual activity predicts auditory recovery from deafness after adult cochlear implantation

Modern cochlear implantation technologies allow deaf patients to understand auditory speech; however, the implants deliver only a coarse auditory input and patients must use long-term adaptive processes to achieve coherent percepts. In adults with post-lingual deafness, the high progress of speech recovery is observed during the first year after cochlear implantation, but there is a large range of variability in the level of cochlear implant outcomes and the temporal evolution of recovery. It has been proposed that when profoundly deaf subjects receive a cochlear implant, the visual cross-modal reorganization of the brain is deleterious for auditory speech recovery. We tested this hypothesis in post-lingually deaf adults by analysing whether brain activity shortly after implantation correlated with the level of auditory recovery 6 months later. Based on brain activity induced by a speech-processing task, we found strong positive correlations in areas outside the auditory cortex. The highest positive correlations were found in the occipital cortex involved in visual processing, as well as in the posterior-temporal cortex known for audio-visual integration. The other area, which positively correlated with auditory speech recovery, was localized in the left inferior frontal area known for speech processing. Our results demonstrate that the visual modalitys functional level is related to the proficiency level of auditory recovery. Based on the positive correlation of visual activity with auditory speech recovery, we suggest that visual modality may facilitate the perception of the words auditory counterpart in communicative situations. The link demonstrated between visual activity and auditory speech perception indicates that visuoauditory synergy is crucial for cross-modal plasticity and fostering speech-comprehension recovery in adult cochlear-implanted deaf patients.

Does Brain Activity at Rest Reflect Adaptive Strategies? Evidence from Speech Processing after Cochlear Implantation

In functional neuroimaging studies, task-related activity refers to the signal difference between the stimulation and rest conditions. We asked whether long-term changes in the sensory environment may affect brain activity at rest. To answer this question, we compared regional cerebral blood flow between a group of normally hearing controls and a group of cochlear-implanted (CI) deaf patients. Here we present evidence that long-term alteration of auditory experience, such as profound deafness followed by partial auditory recuperation through cochlear implantation, leads to functional cortical reorganizations at rest. Without any visual or auditory stimulation, CI subjects showed changes of cerebral blood flow in the visual, auditory cortex, Broca area, and in the posterior temporal cortex with an increment of activity in these areas from the time of activation of the implant to less than a year after the implantation.

Improvement in Speech-Reading Ability by Auditory Training: Evidence from Gender Differences in Normally Hearing, Deaf and Cochlear Implanted Subjects.

Several neuropsychological and neuroimaging studies on gender differences in speech processing lead to the suggestion that women use the neural network of predictive and integrative analysis of speech to a larger extent than men. During speech-reading there is indeed a lack of reliable clues for word recognition which should emphasize predictive and integrative strategies of the brain. Our study aimed to explore gender differences in deaf and cochlear implanted (CI) patients at different levels during speech-reading, for words or phonemes, that we consider, correspond to increased involvement of predictive and integrative analysis. We collected speech-reading scores in a control group of normally hearing subjects (n=42) and in a group of deaf patients - who are good speech-readers - tested before, early after and late after cochlear implantation (n=97). Patient groups were almost equally distributed between follow-up and new patients. In normally hearing controls, women speech-read words better than men. This difference was also observed in all patients but not in experienced cochlear implant users. We did not observe a gender difference during speech-reading of isolated phonemes neither for controls nor for patients. We conclude that the better speech-reading ability of women for words but not for phonemes is in line with their greater use of predictive and integrative strategies for speech processing. Furthermore, we observed a progressive cross-modal compensation in male CI users after cochlear implantation which suggests a synergetic perceptual facilitation involving the visual and the recovering auditory modalities. This could lead to an improved performance in both auditory and visual modalities, the latter being constantly recruited to complement the crude information provided by the implant. Altogether, our data provide insights into cross-modal compensation in the adult brain following sensory privation.

Effects of cosmonaut vestibular training on vestibular function prior to spaceflight

Abstract. The purpose of this study was to quantify the effects of repetitive Coriolis and cross-coupled stimulations, similar to the vestibular training the cosmonauts are exposed to prior to their spaceflight, on vestibular function in control subjects on Earth. Ten volunteers were passively rotated in yaw on a rotating chair while executing standardized pitch head-and-trunk movements. The chair stopped to change direction after 12 head-and-trunk movements were made. The runs were grouped in sessions of ten,which were repeated daily for 10xa0days. The severity of motion sickness was assessed by subjective judgment and measurements of skin pallor and salivary total protein concentration, and nystagmus was recorded. The severity of motion sickness and nystagmus decreased during cosmonaut vestibular training (CVT). Onexa0month after the end of CVT, nystagmus responses were still about 20–30% lower than control values. These results indicate that CVT induces a habituation of vestibular responses. One important implication of this experiment concerns space studies on cosmonauts who are exposed to such vestibular training prior to their spaceflight.

Role of speechreading in audiovisual interactions during the recovery of speech comprehension in deaf adults with cochlear implants.

Speechreading is an important form of communicative activity that improves social adaptation in deaf adults. Cochlear implantation allows interaction between the visual speechreading abilities developed during deafness and the auditory sensory experiences acquired through use of the cochlear implant. Crude auditory information provided by the implant is analyzed in parallel with conjectural information from speechreading, thus creating new profiles of audiovisual integration with implications for brain plasticity. Understanding the peculiarities of change in speechreading after cochlear implantation may improve our understanding of brain plasticity and provide useful information for functional rehabilitation of implanted patients. In this article, we present a generalized review of our recent studies and indicate perspectives for further research in this domain.

Voice discrimination in cochlear-implanted deaf subjects

The human voice is important for social communication because voices carry speech and other information such as a persons physical characteristics and affective state. Further restricted temporal cortical regions are specifically involved in voice processing. In cochlear-implanted deaf patients, the processor alters the spectral cues which are crucial for the perception of the paralinguistic information of human voices. The aim of this study was to assess the abilities of voice discrimination in cochlear-implant (CI) users and in normal-hearing subjects (NHS) using a CI simulation (vocoder). In NHS the performance in voice discrimination decreased when reducing the spectral information by decreasing the number of channels of the vocoder. In CI patients with different delays after implantation we observed a strong impairment in voice discrimination at time of activation of the neuroprosthesis. No significant improvement can be detected in patients after two years of experience of the implant while they have reached a higher level of recovery of speech perception, suggesting a dissociation in the dynamic of functional recuperation of speech and voice processing. In addition to the lack of spectral cues due to the implant processor, we hypothesized that the origin of such deficit could derive from a crossmodal reorganization of the temporal voice areas in CI patients.

PET-imaging of brain plasticity after cochlear implantation.

In this article, we review the PET neuroimaging literature, which indicates peculiarities of brain networks involved in speech restoration after cochlear implantation. We consider data on implanted patients during stimulation as well as during resting state, which indicates basic long-term reorganisation of brain functional architecture. On the basis of our analysis of neuroimaging literature and considering our own studies, we indicate that auditory recovery in deaf patients after cochlear implantation partly relies on visual cues. The brain develops mechanisms of audio-visual integration as a strategy to achieve high levels of speech recognition. It turns out that this neuroimaging evidence is in line with behavioural findings of better audiovisual integration in these patients. Thus, strong visually and audio-visually based rehabilitation during the first months after cochlear implantation would significantly improve and fasten the functional recovery of speech intelligibility and other auditory functions in these patients. We provide perspectives for further neuroimaging studies in cochlear implanted patients, which would help understand brain organisation to restore auditory cognitive processing in the implanted patients and would potentially suggest novel approaches for their rehabilitation. This article is part of a Special Issue entitled .

Increased audiovisual integration in cochlear‐implanted deaf patients: independent components analysis of longitudinal positron emission tomography data

It has been demonstrated in earlier studies that patients with a cochlear implant have increased abilities for audio‐visual integration because the crude information transmitted by the cochlear implant requires the persistent use of the complementary speech information from the visual channel. The brain network for these abilities needs to be clarified. We used an independent components analysis (ICA) of the activation (H215O) positron emission tomography data to explore occipito‐temporal brain activity in post‐lingually deaf patients with unilaterally implanted cochlear implants at several months post‐implantation (T1), shortly after implantation (T0) and in normal hearing controls. In between‐group analysis, patients at T1 had greater blood flow in the left middle temporal cortex as compared with T0 and normal hearing controls. In within‐group analysis, patients at T0 had a task‐related ICA component in the visual cortex, and patients at T1 had one task‐related ICA component in the left middle temporal cortex and the other in the visual cortex. The time courses of temporal and visual activities during the positron emission tomography examination at T1 were highly correlated, meaning that synchronized integrative activity occurred. The greater involvement of the visual cortex and its close coupling with the temporal cortex at T1 confirm the importance of audio‐visual integration in more experienced cochlear implant subjects at the cortical level.