François Champoux

Speech and Non-Speech Audio-Visual Illusions: A Developmental Study

It is well known that simultaneous presentation of incongruent audio and visual stimuli can lead to illusory percepts. Recent data suggest that distinct processes underlie non-specific intersensory speech as opposed to non-speech perception. However, the development of both speech and non-speech intersensory perception across childhood and adolescence remains poorly defined. Thirty-eight observers aged 5 to 19 were tested on the McGurk effect (an audio-visual illusion involving speech), the Illusory Flash effect and the Fusion effect (two audio-visual illusions not involving speech) to investigate the development of audio-visual interactions and contrast speech vs. non-speech developmental patterns. Whereas the strength of audio-visual speech illusions varied as a direct function of maturational level, performance on non-speech illusory tasks appeared to be homogeneous across all ages. These data support the existence of independent maturational processes underlying speech and non-speech audio-visual illusory effects.

Visual stimuli can impair auditory processing in cochlear implant users

It has been shown that visual stimulation can activate cortical regions normally devoted to auditory processing in deaf individuals. This neural activity can persist even when audition is restored through the implantation of a cochlear implant, raising the possibility that cross-modal plasticity can be detrimental to auditory performance in cochlear implant users. To determine the influence of visual information on auditory performance after restoration of hearing in deaf individuals, the ability to segregate conflicting auditory and visual information was assessed in fourteen cochlear implant users with varied degree of expertise and an equal number of participants with normal-hearing matched for gender, age and hearing performance. An auditory speech recognition task was administered in the presence of three incongruent visual stimuli (color-shift, random-dot motion and lip movement). For proficient cochlear implant users, auditory performance was equal to that of controls in the three experimental conditions where visual stimuli were presented simultaneously with auditory information. For non-proficient cochlear implant users, performance did not differ from that of matched controls when the auditory stimulus was paired with a visual stimulus that was color-shifted. However, significant differences were observed between the non-proficient cochlear implant users and their matched controls when the accompanying visual stimuli consisted of a moving random-dot pattern or incongruent lip movements. These findings raise several questions with regards to the rehabilitation of cochlear implant users.

Sensory rehabilitation in the plastic brain

The purpose of this review is to consider new sensory rehabilitation avenues in the context of the brains remarkable ability to reorganize itself following sensory deprivation. Here, deafness and blindness are taken as two illustrative models. Mainly, two promising rehabilitative strategies based on opposing theoretical principles will be considered: sensory substitution and neuroprostheses. Sensory substitution makes use of the remaining intact senses to provide blind or deaf individuals with coded information of the lost sensory system. This technique thus benefits from added neural resources in the processing of the remaining senses resulting from crossmodal plasticity, which is thought to be coupled with behavioral enhancements in the intact senses. On the other hand, neuroprostheses represent an invasive approach aimed at stimulating the deprived sensory system directly in order to restore, at least partially, its functioning. This technique therefore relies on the neuronal integrity of the brain areas normally dedicated to the deprived sense and is rather hindered by the compensatory reorganization observed in the deprived cortex. Here, we stress that our understanding of the neuroplastic changes that occur in sensory-deprived individuals may help guide the design and the implementation of such rehabilitative methods.

Reorganization of auditory cortex in early-deaf people: Functional connectivity and relationship to hearing aid use

Cross-modal reorganization after sensory deprivation is a model for understanding brain plasticity. Although it is a well-documented phenomenon, we still know little of the mechanisms underlying it or the factors that constrain and promote it. Using fMRI, we identified visual motion-related activity in 17 early-deaf and 17 hearing adults. We found that, in the deaf, the posterior superior temporal gyrus (STG) was responsive to visual motion. We compared functional connectivity of this reorganized cortex between groups to identify differences in functional networks associated with reorganization. In the deaf more than the hearing, the STG displayed increased functional connectivity with a region in the calcarine fissure. We also explored the role of hearing aid use, a factor that may contribute to variability in cross-modal reorganization. We found that both the cross-modal activity in STG and the functional connectivity between STG and calcarine cortex correlated with duration of hearing aid use, supporting the hypothesis that residual hearing affects cross-modal reorganization. We conclude that early auditory deprivation alters not only the organization of auditory regions but also the interactions between auditory and primary visual cortex and that auditory input, as indexed by hearing aid use, may inhibit cross-modal reorganization in early-deaf people.

Auditory Processing After Sport-Related Concussions

Objective:The aim of the study is to investigate whether sport-related concussions disrupt auditory processes. Design:Sixteen university athletes participated in the study: eight had one or more sport-related concussions, and eight never experienced a concussion. The Frequency Pattern Sequence test, the Duration Pattern Sequence test, the Synthetic Sentence Identification test, and the Staggered Spondaic Word test were used to assess auditory processing. Results:All nonconcussed athletes have normal auditory processing. In contrast, more than half of the concussed athletes had deficits for one or more of the auditory processing tests. Conclusions:The pattern of results suggests that sport-related concussions can disrupt the neurological mechanisms implicated in several auditory processes, including monaural low-redundancy speech recognition, tone pattern recognition, and dichotic listening.

Enhancement of Visual Motion Detection Thresholds in Early Deaf People

In deaf people, the auditory cortex can reorganize to support visual motion processing. Although this cross-modal reorganization has long been thought to subserve enhanced visual abilities, previous research has been unsuccessful at identifying behavioural enhancements specific to motion processing. Recently, research with congenitally deaf cats has uncovered an enhancement for visual motion detection. Our goal was to test for a similar difference between deaf and hearing people. We tested 16 early and profoundly deaf participants and 20 hearing controls. Participants completed a visual motion detection task, in which they were asked to determine which of two sinusoidal gratings was moving. The speed of the moving grating varied according to an adaptive staircase procedure, allowing us to determine the lowest speed necessary for participants to detect motion. Consistent with previous research in deaf cats, the deaf group had lower motion detection thresholds than the hearing. This finding supports the proposal that cross-modal reorganization after sensory deprivation will occur for supramodal sensory features and preserve the output functions.

Auditory processing in a patient with a unilateral lesion of the inferior colliculus

The role of the inferior colliculus (IC) in human auditory processing is still poorly understood. We report here the results obtained with a 12‐year‐old boy (FX) who suffered a very circumscribed lesion of the right IC without additional neurological damage. The child underwent an extensive battery of psychophysical hearing tests. Results revealed normal peripheral auditory functioning, bilaterally. Furthermore, masking‐level differences and frequency‐pattern recognition were normal for each ear. When the right ear was stimulated, behavioural tests assessing central auditory processing yielded normal results. However, when the left ear was stimulated, speech recognition in the presence of a competing ipsilateral signal and duration‐pattern recognition were impaired. Similarly, performance on two dichotic speech recognition tests was poor when the target stimulus was presented in the left and the competing signal in the right ear. Finally, sound‐source localization in space was deficient for speakers located on the side contralateral to the lesion. The pattern of results suggests that auditory functions such as recognition of low‐redundancy speech presented monaurally, recognition of tone duration patterns, binaural separation and integration, as well as sound‐source localization in space, depend on the integrity of the bilateral auditory pathways at the IC level.

Action related sounds induce early and late modulations of motor cortex activity.

It is now well established that the human brain is endowed with a mechanism that pairs action perception with its execution. This system has been extensively studied using visual stimuli and recent evidence suggests that it is also responsive to the sound of motor actions. Here, we presented action (finger and tongue clicks) and acoustically matched sounds to investigate action-related sound processing in a 12-year-old child undergoing intracranial monitoring of epileptic seizures. Electroencephalography grids were located over a large portion of the right hemisphere, including motor cortex. Wavelet analysis carried out on electrodes overlying the functionally defined hand representation of the motor cortex revealed early (100 ms) and late (250–450 ms) decreases in mu rhythm power (12 and 20 Hz) selective for natural finger-clicks compared with control sounds. These data suggest the presence of a rapid, multimodal resonance mechanism modulating motor cortex activity.

Early- and Late-Onset Blindness Both Curb Audiotactile Integration on the Parchment-Skin Illusion

It has been shown that congenital blindness can lead to anomalies in the integration of auditory and tactile information, at least under certain conditions. In the present study, we used the parchment-skin illusion, a robust illustration of sound-biased perception of touch based on changes in frequency, to investigate the specificities of audiotactile interactions in early- and late-onset blind individuals. Blind individuals in both groups did not experience any illusory change in tactile perception when the frequency of the auditory signal was modified, whereas sighted individuals consistently experienced the illusion. This demonstration that blind individuals had reduced susceptibility to an auditory-tactile illusion suggests either that vision is necessary for the establishment of audiotactile interactions or that auditory and tactile information can be processed more independently in blind individuals than in sighted individuals. In addition, the results obtained in late-onset blind participants suggest that visual input may play a role in the maintenance of audiotactile integration.

Temporary Deafness Can Impair Multisensory Integration A Study of Cochlear-Implant Users

Previous investigations suggest that temporary deafness can have a dramatic impact on audiovisual speech processing. The aim of this study was to test whether temporary deafness disturbs other multisensory processes in adults. A nonspeech task involving an audiotactile illusion was administered to a group of normally hearing individuals and a group of individuals who had been temporarily auditorily deprived. Members of this latter group had their auditory detection thresholds restored to normal levels through the use of a cochlear implant. Control conditions revealed that auditory and tactile discrimination capabilities were identical in the two groups. However, whereas normally hearing individuals integrated auditory and tactile information, so that they experienced the audiotactile illusion, individuals who had been temporarily deprived did not. Given the basic nature of the task, failure to integrate multisensory information could not be explained by the use of the cochlear implant. Thus, the results suggest that normally anticipated audiotactile interactions are disturbed following temporary deafness.