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 Offaxis 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 cues.

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 coding.

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Estimer des distances avec la main-2 Résumé Cette revue critique concerne les processus psychologiques par lesquels nous estimons des distances en utilisant les indices kinesthésiques en l'absence d'informations visuelles. Le paradigme expérimental utilisé par les chercheurs consiste à demander à des sujets (sous occlusion visuelle momentanée) d'explorer avec le système bras-main une distance cible et puis de la reproduire avec la même main. L'analyse des données de la littérature scientifique montre que l'estimation kinesthésique des distances dépend de trois types de facteurs : 1) les indices géométriques, 2) les indices de force et 3) les facteurs cognitifs. De plus, l'analyse des mesures utilisées par les chercheurs pour quantifier cette estimation révèle que les différents types de mesure-l'erreur constante, l'erreur variable et l'erreur absolue-sont traités soit conjointement soit indépendamment. En replaçant ces mesures dans le cadre d'une analyse probabiliste, il apparaît qu'aucune de ces dernières n'est intrinsèquement meilleure que les autres. En réalité, elles font des hypothèses implicites différentes. Discuter de la pertinence de ces mesures d'erreurs revient donc à discuter de la validité de ces hypothèses sous-jacentes, ce qui, heureusement, peut être examiné expérimentalement.