Long Lasting Egocentric Disorientation Induced by Normal Sensori-Motor Spatial Interaction

Perception of the cardinal directions of the body, right-left, up-down, ahead-behind, which appears so absolute and fundamental to the organisation of behaviour can in fact, be modified. Perhaps unsurprisingly, it has been shown that prolonged distorted perception of the orientation of body axes can be a consequence of disordered sensori-motor signals, including long-term prismatic adaptation and lesions of the central nervous system. We report the novel and surprising finding that a long-lasting distortion of perception of personal space can also be induced by an ecological pointing task without the artifice of distorting normal sensori-motor relationships.Twelve right-handed healthy adults performed the task of pointing with their arms, without vision, to indicate their subjective 'straight ahead', a task often used to assess the Egocentric Reference. This was performed before, immediately, and one day after a second task intended to 'modulate' perception of spatial direction. The 'modulating' task lasted 5 minutes and consisted of asking participants to point with the right finger to targets that appeared only in one (right or left) half of a computer screen. Estimates of the 'straight-ahead' during pre-test were accurate (inferior to 0.3 degrees deviation). Significantly, up to one day after performing the modulating task, the subjective 'straight-ahead' was deviated (by approximately 3.2 degrees) to the same side to which subjects had pointed to targets.These results reveal that the perception of directional axes for behaviour is readily influenced by interactions with the environment that involve no artificial distortion of normal sensori-motor-spatial relationships and does not necessarily conform to the cardinal directions as defined by the anatomy of orthostatic posture. We thus suggest that perceived space is a dynamic construction directly dependent upon our past experience about the direction and/or the localisation of our sensori-motor spatial interaction with environment

Les effets consécutifs cognitifs de l'adaptation prismatique visuo-manuelle (de la pseudonégligence à la négligence)

Ce travail de thèse présente la première démonstration d'effets consécutifs cognitifs de l'adaptation prismatique, chez le sujet sain, permettant de proposer un modèle de négligence spatiale unilatérale. L'adaptation prismatique affecte la représentation de l'espace péripersonnel, personnel et la représentation des nombres, suggérant un lien étroit entre l'adaptation prismatique et un noyau commun de représentations spatiales. De plus, ce travail suggère, chez le sujet sain, un lien de causalité entre l'absence de détection consciente du conflit inter-sensoriel et sensori-moteur lors l'exposition aux prismes et le développement d'effets consécutifs amples et durables. L'ensemble de ces résultats, associé à une étude concernant l'adaptation prismatique chez une patiente avec lésion bilatérale du cortex pariétal postérieur supérieur, permet de discuter les structures cérébrales fonctionnellement impliquées dans le développement de l'adaptation prismatique.LYON1-BU.Sciences (692662101) / SudocSudocFranceF

Effets consécutifs de l'adaptation prismatique visuomanuelle au sein de la modalité auditive : Revue et perspectives

International audienceVisuomanual prism adaptation (PA), which consists of pointing to visual targets while wearing prisms that shift the visual field, is one of the oldest experimental paradigms used to investigate sensorimotor plasticity. Since the 2000’s, a growing scientific interest emerged for the expansion of PA to cognitive functions in several sensory modalities. The present work focused on the aftereffects of PA within the auditory modality. Recent studies showed changes in mental representation of auditory frequencies and a shift of divided auditory attention following PA. Moreover, one study demonstrated benefits of PA in a patient suffering from tinnitus. According to these results, we tried to shed light on the following question: How could this be possible to modulate audition by inducing sensorimotor plasticity with glasses? Based on the literature, we suggest a bottom-up attentional mechanism involving cerebellar, parietal, and temporal structures to explain crossmodal aftereffects of PA. This review opens promising new avenues of research about aftereffects of PA in audition and its implication in the therapeutic field of auditory troubles

Vertical prism adaptation, but not sound presentation, modulates the visuospatial representation: A manual line-bisection study

International audienceThe present study aimed at testing whether vertical prism adaptation (PA) can modulate vertical visuospatial representation, assessed with a vertical manual line-bisection (MLB) task (Experiment 1). In a second time, we wanted to investigate the potential influence of sound presentation during such a task. Sound is a spatially valued element that has previously been reported to modify horizontal visuospatial representation. In Experiment 2, we presented either a high pitch, a low pitch, or no sound during the same MLB as in Experiment 1. With this experiment, we also searched for an eventual interaction between the effect of sound presentation and the potential cognitive aftereffects of vertical PA on visual representation.Both Experiments 1 and 2 were constructed with the same design and conducted with two distinct groups of young healthy right-handed participants. First, we assessed the initial sensorimotor state with an open-loop pointing task, and the initial representational state through a vertical MLB (with addition of sound for Experiment 2). Then participants were submitted to a 16-minute PA procedure and were tested again on the open-loop pointing task and the MLB to assess the aftereffects following prism removal.Our results showed sensorimotor aftereffects following both upward and downward PA, in a direction opposed to the optical deviation used. The early aftereffects measured following PA were symmetrical, but at the end of the experiment the residual aftereffects were smaller following downward PA than upward PA. We also provide a new insight on the aftereffects of vertical PA on visuospatial representation, showing that downward PA (but not upward PA) can produce an upward bias on the manual line-bisection task. This is the first proof of such cognitive aftereffects following vertical PA. However, we found no effect of sound presentation on the vertical visual space representation and no interaction between PA and sound presentation

Cognitive bias induced by visuo-motor adaptation to prisms: a simulation of unilateral neglect in normal individuals?

International audienceUnilateral neglect has been recently shown to be improved following a short period of adaptation to wedge prisms. The present study investigates whether visuo-motor adaptation can generate a bias in normals on line bisection tasks classically used to assess unilateral neglect. Our results show that adaptation to left-deviating prisms induces a stronger rightward bias for the perceptual than the motor line bisection task. This bias is in the same direction as the one observed in unilateral neglect. No significant effect is produced by adaptation to right-deviating prisms. Our data confirm that the plasticity of inter-sensory and sensori-motor coordinations affects higher levels of space representation. These asymmetric results may reflect the inherent bias of the brain's structural organisation and provide an empirical explanation for the left-sided predominance of unilateral neglect

Using prism adaptation to alleviate perception of unilateral tinnitus: A case study

International audienceTinnitus is described as an uncomfortable sound or noise heard by an individual in the absence of an external sound source. Treating this phantom perception remains difficult even if drug and nondrug therapies are used to alleviate symptoms. The present case study aimed to investigate whether prism adaptation could induce beneficial aftereffects in a tinnitus sufferer. A 75-year-old man, R. B., with chronic unilateral tinnitus in the left ear reported a self-estimation of parameters of his tinnitus-discomfort, pitch and loudness-and performed a manual line-bisection task to study the consequences of lateralized auditory disorder on spatial representation. Aftereffects of prism adaptation were assessed using a sensorimotor open-loop pointing task. In parallel, a control group completed the line-bisection task and the open-loop pointing task before and after lens exposure, under the same experimental condition as those of R. B. Throughout the pretests, the patient assessed his tinnitus at a constant medium pitch (around 3000 Hz), and he was biased toward the affected ear in both the sensorimotor task and the estimation of the subjective center in the manual line-bisection task. Although both optical deviations were effective, an exposure to prism adaptation to a rightward optical deviation (i.e., toward the unaffected ear) produced stronger aftereffects. In posttests, the tinnitus pitch decreased to 50 Hz and the subjective center was shifted toward the right side (i.e., unaffected ear side). Furthermore, the line-bisection task seemed to reflect the changes in the tinnitus perception, and spatial representation could be a new tool to assess tinnitus indirectly. Our findings suggest that prism adaptation may have benefits on unilateral tinnitus and open a new avenue for its treatment