Is there an oblique effect in the tactual perception of orientation?

This paper surveys studies on the anisotropic perception of orientation in the tactual (cutaneous/passive touch or haptic/active touch) system. In, th e visual system, the vertical and horizontal orientations are known to be p erceived more accurately than oblique orientations. This anisotropy is call ed the oblique effect. The interest of examining the oblique effect in the tactual system stems, in, part, from the fact that even its existence is de bated in the literature. The aim of the present work was to show that : 1 / the study of factors that induce a tactual (cutaneous or haptic) oblique e ffect makes it possible to understand more easily the nature of the tactual underlying processes; 2 / the study of the cutaneous, haptic and visual ob lique effects allows comparisons in the three perceptual systems of the nat ure of the respective processes that underlie the processing of orientation . The first part of this article presents the data on, the oblique effect i n the cutaneous system. The second part concerns the data on the oblique ef fect in the haptic system. We examine the hypothesis that the nature of tas k would influence the oblique effect in the different perceptual systems. W hen the task induces low-level processing, the presence of an anisotropy an d its forms seems to depend on. the properties of orientation-selective neu rons existing at an early stage in the perceptual hierarchy. Thus, an obliq ue effect is present in the visual system, an effect of proximo distal orie ntation (i.e. along the length of the finger) is present in the cutaneous s ystem and no oblique effect is observed in the haptic system. In contrast, when the task induces high-level processing, an oblique effect seems to be present in the cutaneous, haptic and visual systems.