Motor adaptation in deaf and hearing native signers.

Previous studies have suggested that deafness could lead to deficits in motor skills and other body-related abilities. However, the literature regarding motor skills in deaf adults is scarce and existing studies often included participants with heterogeneous language backgrounds and deafness etiologies, thus making it difficult to delineate the effects of deafness. In this study, we investigated motor learning in deaf native signers and hearing nonsigners. To isolate the effects of deafness and those of acquiring a signed language, we additionally tested a group of hearing native signers. Two well-established paradigms of motor learning were employed, in which participants had to adapt their hand movements to a rotation of the visual feedback (Experiment 1) or to the introduction of a force field (Experiment 2). Proprioceptive estimates were assessed before and after adaptation. Like hearing nonsigners, deaf and hearing signers showed robust adaptation in both motor adaptation paradigms. No significant differences in motor adaptation and memory were observed between deaf signers and hearing nonsigners, as well as between hearing signers and hearing nonsigners. Moreover, no discernible group differences in proprioceptive accuracy were observed. These findings challenge the prevalent notion that deafness leads to deficits in motor skills and other body-related abilities.

Reduced multisensory integration of self-initiated stimuli.

The processing and perception of stimuli is altered when these stimuli are not passively presented but rather are actively triggered, or "self-initiated", by the participants. For unimodal stimuli, perceptual changes in stimulus timing and intensity have been demonstrated. Initial results have suggested that self-initiation may affect multisensory processing as well. The present study examined the effects of self-initiation on audiovisual integration in the ventriloquism effect (VE), that is, the mislocalization of auditory stimuli toward a spatially displaced visual stimulus. The effects of self-initiation on the VE were investigated with audiovisual stimuli that featured varying degrees of spatial and temporal separation. Stimuli were either triggered by the participants' button press or not, and stimulus onsets were either predictable or not. Arguing from the perspective of Bayesian causal inference models, we hypothesized self-initiation to increase the prior probability of two stimuli being integrated. Contrary to this intuitive assumption, less VE was observed when the stimuli were self-initiated by the participants than when they were externally generated. Since no effects of self-initiation on unimodal processing were observed, these effects must specifically pertain to multisensory processes. Finally, data were fit with a causal inference model, where self-initiation was associated with a reduction of the prior probability to integrate audiovisual stimuli. In conclusion, the presence of a self-initiated motor signal influences audiovisual integration, such that auditory localization is less biased by visual stimuli, which likely depends on top-down signals.

The role of auditory cortex in the spatial ventriloquism aftereffect.

Cross-modal recalibration allows the brain to maintain coherent sensory representations of the world. Using functional magnetic resonance imaging (fMRI), the present study aimed at identifying the neural mechanisms underlying recalibration in an audiovisual ventriloquism aftereffect paradigm. Participants performed a unimodal sound localization task, before and after they were exposed to adaptation blocks, in which sounds were paired with spatially disparate visual stimuli offset by 14° to the right. Behavioral results showed a significant rightward shift in sound localization following adaptation, indicating a ventriloquism aftereffect. Regarding fMRI results, left and right planum temporale (lPT/rPT) were found to respond more to contralateral sounds than to central sounds at pretest. Contrasting posttest with pretest blocks revealed significantly enhanced fMRI-signals in space-sensitive lPT after adaptation, matching the behavioral rightward shift in sound localization. Moreover, a region-of-interest analysis in lPT/rPT revealed that the lPT activity correlated positively with the localization shift for right-side sounds, whereas rPT activity correlated negatively with the localization shift for left-side and central sounds. Finally, using functional connectivity analysis, we observed enhanced coupling of the lPT with left and right inferior parietal areas as well as left motor regions following adaptation and a decoupling of lPT/rPT with contralateral auditory cortex, which scaled with participants' degree of adaptation. Together, the fMRI results suggest that cross-modal spatial recalibration is accomplished by an adjustment of unisensory representations in low-level auditory cortex. Such persistent adjustments of low-level sensory representations seem to be mediated by the interplay with higher-level spatial representations in parietal cortex.