Haptic perception of spatial relations

There are some indications that haptic space like visual space is not Eucli dean (eg Blumenfeld, 1937 Acta Psychologica 2 125-174). In a series of expe riments, we investigated the haptic perception of spatial relations in a sy stematic way. We restricted ourselves to a horizontal plane at waist height . Blindfolded subjects were asked to perform three tasks with their right h and: (i) a reference bar was presented under four different orientations an d subjects were asked to rotate a test bar such that it felt to be parallel to the reference bar; (ii) subjects had to rotate two test bars in such a way that they felt collinear; (iii) subjects had to point a test bar in the direction of a marker. Bars and marker could appear at nine different loca tions. In all experiments large systematic deviations (up to 40 degrees) we re made. The deviations strongly correlated with horizontal (right-left) bu t not with vertical (forward-backward) distance. Subjects showed qualitativ ely identical trends but the size of the deviations was strongly subject-de pendent. In addition, a significant haptic oblique effect was found. These results provide strong evidence that haptic space in non-Euclidean.