Factors affecting the size of the detour effect in the kinaesthetic perception of Euclidean distance

Three experiments investigated the mechanisms by which we estimate Euclidean distances on the basis of kinaesthetic cues. In all experiments, blindfolded participants followed straight and curvilinear paths with a stylus. Then, with a straight response movement, they estimated the distance between the end-points of the previously explored path. Experiment 1 was designed to validate the hypothesis—made on the basis of results from a previous study—that errors in the kinaesthetic estimations of distances (detour effect) originate from the difficulty to decompose the displacement vector into relevant and irrelevant components, which would become more severe at points of inflection. Using elliptic paths (no inflections), we demonstrated that errors are indeed reduced considerably. The role of the orientation of the work plane was investigated in Experiment 2 in which the same paths used in our previous study were oriented in the frontal rather than the horizontal plane. The results indicate that the detour effect is independent of the orientation. Moreover, despite the asymmetry that gravity introduces between upward and downward movements, errors in the two directions are almost identical. Experiment 3 addressed two issues. First, we demonstrated that introducing a delay between the exploration of the path and the response did not alter significantly the pattern of errors. By contrast, we demonstrated that errors are severely reduced when the number of paths to be explored is reduced by half. The results of the three experiments are discussed within the context of current theories of sensori-motor codin

The kinaesthetic perception of Euclidean distance: a study of the detour effect

An experiment investigated the mechanisms by which humans estimate Euclidean distances on the basis of kinaesthetic cues. Blindfolded participants followed straight and curvilinear paths with a hand-held stylus (encoding phase). Then, with a straight movement, they estimated the Euclidean distance between the start- and end-points of the path (response phase). The experiment contrasted an On-axis condition, in which encoding and response movements were spatially aligned, and an Off-axis condition, in which they were displaced laterally. Performances were slightly more accurate in the On-axis condition than in the Off-axis condition. In both conditions, however, errors were consistently smaller when the path covered a larger surface. The results showed that small paths yielded an overestimation of the Euclidean distance, the relative errors increasing with the length of curvilinear paths. The findings are compared with results of other studies in which distances were estimated on the basis of haptic cue

Effect of selective and distributed training on visual identification of orientation

An experiment contrasted the effect of four training schedules in a visual orientation reproduction task. Two selective schedules involved repeated presentation of a single target orientation. Two non-selective schedules involved targets covering the first quadrant either at fixed, equispaced orientations, or distributed randomly. In pre-training sessions, we observed the classical oblique effect (precision for vertical and horizontal stimuli higher than for oblique ones). Practice improved precision with both distributed schedules, but was ineffectual for non-selective schedules. However, a significant oblique effect persisted under all conditions. We argue that the pattern of results is compatible with the hypothesis that the oblique effect reflects both the intrinsic neuronal properties of the primary visual system, and the structure of the visual space imposed by higher, more cognitive processes. The results challenge the thesis that only attentional and post-perceptual factors are able to affect the working of the early visual syste

Short paper : Role of force-cues in path following of 3D trajectories in Virtual Reality.

International audienceThis paper examines the effect of adding haptic force cues (simulated inertia, compensation of gravity) during 3D-path following in large immersive virtual reality environments. Thirty-four participants were asked to follow a 3D ring-on-wire trajectory. The experiment consisted of one pre-test/control bloc of twelve trials with no haptic feedback; followed by three randomized blocs of twelve trials, where force feedbacks differed. Two levels of inertia were proposed and one level compensating the effect of gravity (No-gravity). In all blocks, participants received a real time visual warning feedback (color change), related to their spatial performance. Contrariwise to several psychophysics studies, haptic force cues did not significantly change the task performance in terms of time completion or spatial distance error. The participants however significantly reduced the time passed in the visual warning zone in the presence of haptic cues. Taken together, these results are discussed from a psychophysics and multi-sensory integration point of view

The Haptic Recognition of Geometrical Shapes in Congenitally Blind and Blindfolded Adolescents: Is There a Haptic Prototype Effect?

International audienceBACKGROUND: It has been shown that visual geometrical shape categories (rectangle and triangle) are graded structures organized around a prototype as demonstrated by perception and production tasks in adults as well as in children. The visual prototypical shapes are better recognized than other exemplars of the categories. Their existence could emerge from early exposure to these prototypical shapes that are present in our visual environment. The present study examined the role of visual experience in the existence of prototypical shapes by comparing the haptic recognition of geometrical shapes in congenitally blind and blindfolded adolescents. METHODOLOGY/PRINCIPAL FINDINGS: To determine whether the existence of a prototype effect (higher recognition of prototypical shapes than non prototypical shapes) depended on visual experience, congenitally blind and blindfolded sighted adolescents were asked to recognize in the haptic modality three categories of correct shapes (square, rectangle, triangle) varying in orientation (prototypical/canonical orientation vs. non prototypical/canonical orientation rotated by 45°) among a set of other shapes. A haptic prototype effect was found in the blindfolded sighted whereas no difference between prototypical and non prototypical correct shapes was observed in the congenitally blind. A control experiment using a similar visual recognition task confirmed the existence of a visual prototype effect in a group of sighted adolescents. CONCLUSION/SIGNIFICANCE: These findings show that the prototype effect is not intrinsic to the haptic modality but depends on visual experience. This suggests that the occurrence of visual and haptic prototypical shapes in the recognition of geometrical shape seems to depend on visual exposure to these prototypical shapes existing in our environment

The Visual Localization of the Centre of Triangles in Young Children and Adults

La notion de centre est ambiguë pour la plupart des formes géométriques. Pour étudier cette question, nous avons demandé à des enfants âgés de cinq ans et à des adultes de marquer le centre d'un triangle sur une feuille de papier. Les réponses des deux groupes étaient très similaires. Premièrement, les deux groupes tendaient à percevoir le centre du triangle rectangle à mi-distance entre le centre de masse et le centre du cercle inscrit. Deuxièmement, la position du centre du triangle équilatéral était déplacée en direction de la pointe opposée au côté horizontal. Ces résultats suggèrent que la localisation visuelle du  centre de triangles dépend de processus perceptifs de bas-niveau, déjà en place à l'âge de cinq ans.The ambiguity of the notion of centre for most shapes raises the question of whether children perceive the centre of a shape in the same place as adults. To answer this question, we asked five- year old children and adults to mark the centre of a triangle with a pen. The responses of children and adults were strikingly similar. First, the two groups perceived the centre of right triangles at mid-distance between the centre of mass and the centre of the inscribed circles. Second, the perceptual centre of the equilateral triangle was shifted toward the vertex that opposed the horizontal edge of the triangle for children and adults alike. These results suggest that the visual localization of the centre of triangles would depend on low-level sensori-motor processes that are in place since at least the age of five

Vibrotactile guidance for trajectory following in computer aided surgery.

International audienceMost conventional computer-aided navigation systems assist the surgeon visually by tracking the position of an ancillary and by superposing this position into the 3D preoperative imaging exam. This paper aims at adding to such navigation systems a device that will guide the surgeon towards the target, following a complex preplanned ancillary trajectory. We propose to use tactile stimuli for such guidance, with the design of a vibrating belt. An experiment using a virtual surgery simulator in the case of skull base surgery is conducted with 9 naïve subjects, assessing the vibrotactile guidance effectiveness for complex trajectories. Comparisons between a visual guidance and a visual+tactile guidance are encouraging, supporting the relevance of such tactile guidance paradigm

The Visual and the Haptic Müller-Lyer Illusions: Correlation Study

Cette recherche s’intéresse à l’illusion de Müller-Lyer dans les modalités visuelle et haptique (tactilo-kinesthésique). Nous avons examiné si les performances corrèlent quand les mêmes participants effectuent la même tâche dans les deux modalités. Les participants devaient explorer visuellement ou haptiquement un stimulus composé de deux pennures fixées au bout d’une baguette et orientées vers leur gauche et d’une troisième pennure mobile et orientée vers leur droite.  Les participants donnaient des instructions verbales à l’expérimentateur de manière à ce qu’il place cette troisième pennure au milieu de la baguette. Les résultats révèlent une corrélation positive entre les classiques erreurs perceptives observées dans les deux modalités. De plus, les temps de réponse obtenus dans les deux tâches corrèlent aussi positivement. Les résultats apportent des arguments en faveur de l’hypothèse de processus communs responsables de l’illusion de Müller-Lyer dans les modalités visuelle et haptique.This study examines the Müller-Lyer illusion in the visual and haptic modalities. We investigated whether positive correlations between performances would be observed when the same participants performed exactly the same task in both modalities. The participants were asked to explore first visually only and then haptically only (or in the reverse order) a display made of two arrowheads fixed at the end of rod which pointed to their left. Then, the participants were asked to give verbal instructions to the experimenter who moved the “central and third arrowhead” until they thought that its apex bisected the length of the rod. Results revealed the presence of a significant positive correlation between the classical errors observed in the two modalities. Moreover, the response time for the visual task was also positively correlated to the time for the haptic one. The results are discussed in relation to the hypothesis assuming that common processes underlie the Müller-Lyer illusion in vision and haptics