Motor processes in mental rotation

Much indirect evidence supports the hypothesis that transformations of mental images are at least in part guided by motor processes, even in the case of images of abstract objects rather than of body parts. For example, rotation may be guided by processes that also prime one to see results of a specific motor action. We directly test the hypothesis by means of a dual-task paradigm in which subjects perform the Cooper-Shepard mental rotation task while executing an unseen motor rotation in a given direction and at a previously learned speed. Four results support the inference that mental rotation relies on motor processes. First, motor rotation that is compatible with mental rotation results in faster times and fewer errors in the imagery task than when the two rotations are incompatible. Second, the angle through which subjects rotate their mental images, and the angle through which they rotate a joystick handle are correlated, but only if the directions of the two rotations are compatible. Third, motor rotation modifies the classical inverted V-shaped mental rotation response time function, favoring the direction of the motor rotation; indeed, in some cases motor rotation even shifts the location of the minimum of this curve in the direction of the motor rotation. Fourth, the preceding effect is sensitive not only to the direction of the motor rotation, but also to the motor speed. A change in the speed of motor rotation can correspondingly slow down or speed up the mental rotation

Combined Induction of Rubber-Hand Illusion and Out-of-Body Experiences

The emergence of self-consciousness depends on several processes: those of body ownership, attributing self-identity to the body, and those of self-location, localizing our sense of self. Studies of phenomena like the rubber-hand illusion (RHi) and out-of-body experience (OBE) investigate these processes, respectively for representations of a body-part and the full-body. It is supposed that RHi only target processes related to body-part representations, while OBE only relates to full-body representations. The fundamental question whether the body-part and the full-body illusions relate to each other is nevertheless insufficiently investigated. In search for a link between body-part and full-body illusions in the brain we developed a behavioral task combining adapted versions of the RHi and OBE. Furthermore, for the investigation of this putative link we investigated the role of sensory and motor cues. We established a spatial dissociation between visual and proprioceptive feedback of a hand perceived through virtual reality in rest or action. Two experimental measures were introduced: one for the body-part illusion, the proprioceptive drift of the perceived localization of the hand, and one for the full-body illusion, the shift in subjective-straight-ahead (SSA). In the rest and action conditions it was observed that the proprioceptive drift of the left hand and the shift in SSA toward the manipulation side are equivalent. The combined effect was dependent on the manipulation of the visual representation of body parts, rejecting any main or even modulatory role for relevant motor programs. Our study demonstrates for the first time that there is a systematic relationship between the body-part illusion and the full-body illusion, as shown by our measures. This suggests a link between the representations in the brain of a body-part and the full-body, and consequently a common mechanism underpinning both forms of ownership and self-location

On the mechanical contribution of head stabilization to passive dynamics of anthropometric walkers

During the steady gait, humans stabilize their head around the vertical orientation. While there are sensori-cognitive explanations for this phenomenon, its mechanical e fect on the body dynamics remains un-explored. In this study, we take profit from the similarities that human steady gait share with the locomotion of passive dynamics robots. We introduce a simplified anthropometric D model to reproduce a broad walking dynamics. In a previous study, we showed heuristically that the presence of a stabilized head-neck system significantly influences the dynamics of walking. This paper gives new insights that lead to understanding this mechanical e fect. In particular, we introduce an original cart upper-body model that allows to better understand the mechanical interest of head stabilization when walking, and we study how this e fect is sensitive to the choice of control parameters

The autoscopic flying avatar: a new paradigm to study bilocated presence in mixed reality

This position paper presents the project "Becoming Avatar" deals with avatarial immersion [1] addressed through an interdisciplinary experimental approach. Its goal, at the crossroad of the creation of images and interactive technology, of virtual reality, neurophysiology and information and communication sciences, is to develop a device and a media scenario to support the hypothesis of a split state and to objectify the situation of bilocation [2]. Being present both here in front of the screen and over there, beyond the screen, which is shown by empirical studies of video games and by artists and metaverse explorers in Second Life. This type of state resonates in neurophysiology with the artificial "Out-of-Body Experiences" sensations produced with the aid of virtual reality equipment on healthy subjects. The production includes the development of a scientific experimental facility for physiological measurements and a public installation allowing someone to live a non-ordinary experience of split self. The common feature to both aspects of the project is based on the original idea of integrating video and 3D technology in order to experiment a situation of flight in mixed reality. The subject is literally invited to "become an avatar", indeed, he sees his own image, filmed from behind, inlaid into a synthetic world where he will be able to move freely and experiment different events. This autoscopic system of immersion was imagined in 2012 by E. Pereny and worked again in 2013-2014 with Pr A. Berthoz and E.A. Amato, to be developed and finalized with N. Galinotti and G. Gorisse, with Jams sessions integrating students

Driver trust and reliance on a navigation system: Effect of graphical display

International audienceThe present study investigates the influence of in-car navigation system graphic’s appearance on driver trust and reliance on the system. Two navigation systems were used: one with a realistic interface and one with a symbolic interface. During driving sessions on a simulator, the systems committed some guidance incoherencies regarding road signs present in the virtual environment. Subject’s trust and reliance on navigation systems were measured and compared between both systems. Result showed a higher level of trust for the realistic appearance system than for the symbolic one during the whole experiment. The presence of incoherencies decreased trust level for both systems but without any significant difference. No difference in system’s reliance was found but two groups of subjects were identified. One group is highly relying on both navigation systems’ indication when incoherence occurs whereas the other group was not. This study highlights the interaction of subjective items, as system graphical appearance, on user trust. Further experiments using a modified experimental setup may be needed to analyze precisely the influence on user relianceCette étude analyse l’influence de l’apparence graphique d’un système d’aide à la navigation sur le niveau de confiance et d’utilisation du système par le conducteur. Deux systèmes d’aide sont utilisés : un avec une interface graphique réaliste, et un avec une interface graphique simpliste. Durant des sessions de conduite réalisées sur simulateur, des incohérences dans le guidage du système vis-à-vis des panneaux présent dans l’environnement routier seront commises. Le niveau de confiance des sujets envers le système et son utilisation sont enregistrés et comparés entre les deux systèmes d’aide à la navigation. Les résultats montrent un niveau de confiance plus élevé tout au long de l’expérience pour le système avec une interface graphique réaliste. La présence d’incohérences de guidage engendre bien une diminution du niveau de confiance mais sans différence notable entre les deux systèmes. Aucune différence du niveau d’utilisation n’est enregistrée mais deux groupes de sujets sont identifiés. Un groupe de sujets se fie largement aux directions indiquées par les deux systèmes lors des incohérences, alors que l’autre groupe non. Cette étude souligne les interactions d’éléments subjectifs, comme l’apparence graphique d’un système, sur le niveau de confiance de l’utilisateur. Une autre phase expérimentale utilisant un protocole modifié serait nécessaire pour analyser en détail l’influence sur le niveau d’utilisation du système

Spatial memory of paths using circular probability distributions: Theoretical properties, navigation strategies and orientation cue combination

International audienceWe propose a mathematical model of the Path Integration (PI) process. Its core assumption is that orientations of a path are summarized by circular probability distributions. We compare our model with classical, deterministic models of PI and find that, although they are indistinguishable in terms of information encoded, the probabilistic model is more parsimonious when considering navigation strategies. We show how sensory events can enrich the probability distributions memorized, resulting in a continuum of navigation strategies, from PI to stimulus-triggered response. We analyze the combination of circular probability distributions (e.g., multicue fusion), and demonstrate that, contrary to the linear case, adding orientation cues does not always increase reliability of estimates. We discuss experimental predictions entailed by our model

Differences in gaze anticipation for locomotion with and without vision

International audiencePrevious experimental studies have shown a spontaneous anticipation of locomotor trajectory by the head and gaze direction during human locomotion. This anticipatory behavior could serve several functions: an optimal selection of visual information, for instance through landmarks and optic flow, as well as trajectory planning and motor control. This would imply that anticipation remains in darkness but with different characteristics. We asked 10 participants to walk along two predefined complex trajectories (limaçon and figure eight) without any cue on the trajectory to follow. Two visual conditions were used: (i) in light and (ii) in complete darkness with eyes open. The whole body kinematics were recorded by motion capture, along with the participant's right eye movements. We showed that in darkness and in light, horizontal gaze anticipates the orientation of the head which itself anticipates the trajectory direction. However, the horizontal angular anticipation decreases by a half in darkness for both gaze and head. In both visual conditions we observed an eye nystagmus with similar properties (frequency and amplitude). The main difference comes from the fact that in light, there is a shift of the orientations of the eye nystagmus and the head in the direction of the trajectory. These results suggest that a fundamental function of gaze is to represent self motion, stabilize the perception of space during locomotion, and to simulate the future trajectory, regardless of the vision condition