The manual haptic perception of orientations and the oblique effect in patients with left visuo-spatial neglect

Abstract

This study addresses the limits of haptic orientation deficit observed in patients with left visuo-spatial neglect (VSN) in the fronto-parallel plane. We concentrated on two aspects of the haptic perception of vertical, horizontal and oblique orientations: first, the global level of performances compared with normal subjects and, second, the occurrence of the oblique effect (i.e. lower performances in oblique orientations than in vertical-horizontal orientations). Subjects were asked to position a rod, presented in the fronto-parallel plane, to one of four orientations: vertical, horizontal, left 45 degrees oblique and right 45 degrees oblique. First, we found a haptic orientation deficit in neglect patients: The precision was lower in the neglect patients than in the normal (young adults and seniors) subjects. Second, we observed in both neglect patients and control subjects the occurrence of a similar haptic oblique effect and there were no differences between the results in the left and right hemispaces. Taken together, this means that, in spite of the global haptic orientation production deficit observed in VSN patients, no specific pattern was observed in the haptic production of different orientations in these subjects as compared to the two other groups. The haptic orientation deficit of neglect patients seems to affect in the same way all values and spatial positions of orientations.

The structure of frontoparallel haptic space is task dependent

“…When the participants' heads were in a vertical position, they did not make systematic errors, but oblique orientations were produced with greater variability. Gentaz, Badan, Luyat, and Touil (2002) asked healthy human participants and neglect patients to produce each of the four main orientations at each of two positions (20 cm to the left or 20 cm to the right of the body midline). For the vertical and the 45º oblique orientations, systematic errors were made that were absent for the horizontal and Ϫ45º orientations.…”

The role of contextual cues in the haptic perception of orientations and the oblique effect

“…This anisotropy, called the oblique effect by Appelle (1972), is present whatever the perceptual system involved in the perceptual judgment. It has been found with a great variety of tasks in visual (Attneave & Olson, 1967;Furmanski & Engel, 2000;Gentaz et al, 2001;McIntyre, Lipshits, Zaoui, Berthoz, & Gurfinkel, 2001;McMahon & MacLeod, 2003;Westheimer, 2003), haptic (Appelle & Countryman, 1986;Gentaz, Badan, Luyat, & Touil, 2002;Gentaz & Hatwell, 1995, 1999Gentaz & Streri, 2004;Hermens & Gielen, 2003;Kappers, 1999;Kappers & Koenderink, 1999;Lechelt & Verenka, 1980;Luyat, Gentaz, Regia Corte, & Guerraz, 2001), and somatovestibular systems.…”

Influence of Shape Elements on Performance During Haptic Rotation

“…Research on haptic perception of orientations [5,15] includes investigations on the oblique effect [4,6,7,8] and on parallelism [10,11,13,16]. The oblique effect describes that vertical or horizontal orientations are better processed by humans than oblique orientations, such as 45 or 135 degrees.…”

“…Other studies had participants produce verbally ordered orientations [4,14]. In experiments in which the perception of parallelism is investigated, e.g.…”

“…Previous research used rods or bars for control [2,3,4,6,7,8,10,11,12,13,14,16], whose shape continually provides information about their orientation. In this work, participants manipulate rotary knobs, which allow us to control the information on the control's orientation as opposed to the non-uniform shape of bars.…”