What have We Learned from “Perturbing” the Human Cortical Motor System with Transcranial Magnetic Stimulation?

The purpose of this paper is twofold. First, we will review different approaches that one can use with transcranial magnetic stimulation (TMS) to study both its effects on motor behavior and on neural connections in the human brain. Second, we will present evidence obtained in TMS-based studies showing that the dorsal premotor area (PMd), the ventral premotor area (PMv), the supplementary motor area (SMA), and the pre-supplementary motor area (pre-SMA) each have different roles to play in motor behavior. We highlight the importance of the PMd in response selection based on arbitrary cues and in the control of arm movements, the PMv in grasping and in the discrimination of bodily actions, the SMA in movement sequencing and in bimanual coordination, and the pre-SMA in cognitive control. We will also discuss ways in which TMS can be used to chart “true” cerebral reorganization in clinical populations and how TMS might be used as a therapeutic tool to facilitate motor recovery after stroke. We will end our review by discussing some of the methodological challenges and future directions for using this tool in basic and clinical neuroscience

Susceptibility to optical illusions varies as a function of the autism-spectrum quotient but not in ways predicted by local–global biases

Individuals with autism spectrum disorder and those with autistic tendencies in non-clinical groups are thought to have a perceptual style privileging local details over global integration. We used 13 illusions to investigate this perceptual style in typically developing adults with various levels of autistic traits. Illusory susceptibility was entered into a principal-component analysis. Only one factor, consisting of the Shepard’s tabletops and Square-diamond illusions, was found to have reduced susceptibility as a function of autistic traits. Given that only two illusions were affected and that these illusions depend mostly on the processing of within-object relational properties, we conclude there is something distinct about autistic-like perceptual functioning but not in ways predicted by a preference of local over global elements

Les différentes stratégies communicationnelles favorisant les changements de comportements en matière de changements climatiques

La cause anthropique des changements climatiques fait maintenant consensus au sein de la communauté scientifique. Des décisions doivent être prises pour atténuer les conséquences engendrées par cette problématique. Au fil des ans, plusieurs organismes environnementaux ont véhiculé l’importance d’agir rapidement pour préserver l’environnement. Cependant, peu d’actions semblent être entreprises pour répondre adéquatement à l’urgence de la situation. Plusieurs facteurs peuvent justifier l’état d’inaction et doivent être adressés pour créer une formule engageante auprès de la population. Une approche communicationnelle adaptée joue donc un rôle essentiel pour promouvoir l’adoption de nouveaux comportements pro-environnementaux. Cet essai a pour objectif principal de cibler les stratégies de communication les plus efficaces en matière de changements climatiques pour entraîner un changement de comportements auprès de la population. Pour ce faire, les modèles théoriques de changement comportemental et les principales méthodes communicationnelles sont présentés. Par la suite, quatre projets visant à modifier les comportements dirigés par des organismes environnementaux québécois ont été sélectionnés. Avec les informations préalablement recueillies, une grille d’analyse a été créée afin d’évaluer les stratégies de communication utilisées par « Action citoyenne à vélo », « À vos ruelles vertes », « Côte-à-Côte », et « Embarque Lanaudière » menés respectivement par Environnement Jeunesse, Nature-Québec, le ZIP du Sud-de-l’Estuaire et le Conseil régional de l’environnement de Lanaudière. La grille d’analyse inclut les thèmes de cadrage et les procédés persuasifs principalement utilisés lors des communications des projets de même que les indicateurs d’efficacité qui ont été sollicités. Les thèmes utilisés par ces organismes se centraient essentiellement sur l’environnement et la santé. Les procédés persuasifs majoritairement utilisés consistaient à favoriser l’autonomisation, à susciter l’espoir et à recourir à la notion de gains et pertes. Afin d’assurer une meilleure efficacité des stratégies communicationnelles liées aux changements climatiques, quatre recommandations ont été émises. Il est ainsi suggéré d’apprendre à bien connaître son public cible, inventorier les informations relatives aux communications, utiliser les connaissances scientifiques et, finalement, élaborer des objectifs précis ciblant les communications du projet. Pour conclure, en diversifiant les approches et en les adaptant à la population ciblée, le niveau d’engagement dans de nouveaux comportements environnementaux sera optimisé

Perceptual Discrimination of Basic Object Features Is Not Facilitated When Priming Stimuli Are Prevented From Reaching Awareness by Means of Visual Masking

Our understanding of how form, orientation and size are processed within and outside of awareness is limited and requires further investigation. Therefore, we investigated whether or not the visual discrimination of basic object features can be influenced by subliminal processing of stimuli presented beforehand. Visual masking was used to render stimuli perceptually invisible. Three experiments examined if visible and invisible primes could facilitate the subsequent feature discrimination of visible targets. The experiments differed in the kind of perceptual discrimination that participants had to make. Namely, participants were asked to discriminate visual stimuli on the basis of their form, orientation, or size. In all three experiments, we demonstrated reliable priming effects when the primes were visible but not when the primes were made invisible. Our findings underscore the importance of conscious awareness in facilitating the perceptual discrimination of basic object features

The contribution of linear perspective cues and texture gradients in the perceptual rescaling of stimuli inside a Ponzo illusion corridor

We examined the influence of linear perspective cues and texture gradients in the perceptual rescaling of stimuli over a highly-salient Ponzo illusion of a corridor. We performed two experiments using the Method of Constant Stimuli where participants judged the size of one of two rings. In experiment 1, one ring was presented in the upper visual-field at the end of the corridor and the other in the lower visual-field at the front of the corridor. The perceived size of the top and bottom rings changed as a function of the availability of linear perspective and textures. In experiment 2, only one ring was presented either at the top or the bottom of the image. The perceived size of the top but not the bottom ring changed as a function of the availability of linear perspective and textures. In both experiments, the effects of the cues were additive. Perceptual rescaling was also stronger for the top compared to the bottom ring. Additional eye-tracking revealed that participants tended to gaze more in the upper than the lower visual-field. These findings indicate that top-down mechanisms provide an important contribution to the Ponzo illusion. Nonetheless, additional maximum likelihood estimation analyses revealed that linear perspective fulfilled a greater contribution in experiment 2, which is suggestive of a bottom-up mechanism. We conclude that both top-down and bottom-up mechanisms play important roles. However, the former seems to fulfil a more prominent role when both stimuli are presented in the image

The Shepard Illusion Is Reduced in Children With an Autism Spectrum Disorder Because of Perceptual Rather Than Attentional Mechanisms

Earlier studies demonstrate reduced illusion strength in the Shepard illusion in adults and adolescents with an autism spectrum disorder (ASD) and in typically developing (TD) adults with high levels of autistic traits. We measured the strength of the Shepard illusion in ASD and TD children and tested if ten different eye-tracking measurements could predict group differences in illusion strength. The ASD children demonstrated reduced illusion strength relative to the TD group. Despite this, there were no mean differences on any of the eye-tracking measurements between groups. Even though none of the eye-tracking measurements revealed mean differences between the two groups, the degree to which spatial attention was directed toward the standard stimulus, as indexed by the number of saccades within and toward this stimulus, predicted the strength of the illusion in the overall sample. Furthermore, this active scanning of the standard stimulus was found to enhance illusion strength more strongly in the ASD than the TD group. Together, we conclude that scan patterns and the degree to which participants are able to shift between different locations in a visual scene did not account for group differences in illusion strength. Thus, the reduced strength of the Shepard illusion in ASD does not appear to be driven by how attention shifts or is spatially allocated. Rather, differences may relate instead to perceptual mechanisms that integrate visual information. Strategies that may aid ASD individuals to see this illusion more strongly could have them make even more eye movements within and between the stimuli presented in the illusion display

Evaluating bodily self-consciousness and the brain using multisensory perturbation and fMRI

In this article, we consider the usefulness of functional magnetic resonance imaging (fMRI) and perturbation in evaluating causal relationships between bodily self-consciousness and the brain. We argue that fMRI research is not always restricted to correlational statements when it is combined with perturbation techniques and can sometimes permit some degree of causal inferencing, such as when bodily illusions are examined with fMRI. In these instances, one is changing a participant’s conscious bodily self by experimentally perturbing mechanisms that are involved in multisensory integration

Rapid decrement in the effects of the Ponzo display dissociates action and perception.

It has been demonstrated that pictorial illusions have a smaller influence on grasping than they do on perceptual judgments. Yet to date this work has not considered the reduced influence of an illusion as it is measured repeatedly. Here we studied this decrement in the context of a Ponzo illusion to further characterize the dissociation between vision for perception and for action. Participants first manually estimated the lengths of single targets in a Ponzo display with their thumb and index finger, then actually grasped these targets in another series of trials, and then manually estimated the target lengths again in a final set of trials. The results showed that although the perceptual estimates and grasp apertures were equally sensitive to real differences in target length on the initial trials, only the perceptual estimates remained biased by the illusion over repeated measurements. In contrast, the illusion\u27s effect on the grasps decreased rapidly, vanishing entirely after only a few trials. Interestingly, a closer examination of the grasp data revealed that this initial effect was driven largely by undersizing the grip aperture for the display configuration in which the target was positioned between the diverging background lines (i.e., when the targets appeared to be shorter than they really were). This asymmetry between grasping apparently shorter and longer targets suggests that the sensorimotor system may initially treat the edges of the configuration as obstacles to be avoided. This finding highlights the sensorimotor system\u27s ability to rapidly update motor programs through error feedback, manifesting as an immunity to the effects of illusion displays even after only a few trials

Méthodes d’optimisation du système PCL

Cet article expose des solutions pour pallier les deux difficultés majeures qu’engendre l’emploi d’un système de détection passive cohérente ; soit la forte interférence causée par le signal direct, annulée par la projection dans un sous-espace complémentaire à celui-ci, et la faiblesse de l’écho de la cible, solutionnée par l’utilisation d’un réseau d’antennes à chevauchement d’éléments formant des sous-réseaux. Les expressions mathématiques de la matrice de covariance du signal et du bruit sont présentées pour expliquer le comportement de la sortie du filtre adapté selon le nombre de sous-réseaux employé. À partir de l’expression analytique de la valeur propre, on dérive une expression analytique permettant d’établir le nombre de sous-réseaux à employer en fonction de l’orientation de la cible et du nombre d’éléments d’antenne disponibles afin d’optimiser la sortie du filtre adapté.This paper expose soultions to mitigate the two major difficulties caused by the use of a passive coherent location system, namely the strong interference from the direct signal, canceled by the projection in a subspace complementary to the direct signal subspace, and the weakness of the target echo, resolve by using an overlapped antenna array made up of subarrays. The mathematical expressions of the signal covariance matrix and the noise covariance matrix are presented to describe the behavior of the matched filter output according to the number of subarrays employed. From the analytical expression of the eigenvalues, an equation is presented that determine the optimal number of subarrays to be used according to orientation of the target and to the number of antennae elements available to optimize the matched filter out