Misdirections in slow goal-directed arm movements and pointer-setting tasks

Abstract

Information about the direction of the virtual line between two positions in space (directional information) is used in many decision-making and motor tasks. We investigated how accurately directional information is processed by the brain. Subjects performed two types of task. In both tasks they sat at a table. In the first task they had to move their hand slowly and accurately from an initial position 40 cm in from of them to visually presented targets at a distance of 30 cm from the initial position (movement task). We analysed the initial movement direction. In the second task subjects had to position pointers in the direction of the targets as accurately as they could (perceptive task). We found that in the movement task the subjects started the movements to most targets in a direction that deviated consistently from the direction of the straight line between initial position and target position. The maximum deviation ranged from 5-10 degrees for the various subjects. The mean standard deviation was 4 degrees. In the perceptive task the subjects positioned the pointer in similarly deviating directions. Furthermore, we found that the maximum deviation in the pointer direction depended on the length of the pointer: the smaller the pointer, the larger the consistent deviations in the pointer direction. The shortest pointer showed deviations comparable to the deviations found in the movement task. These findings suggest that the deviations in the two tasks stem from the same source.

Independent sources of anisotropy in visual orientation representation: a visual and a cognitive oblique effect

“…In a series of studies of spatial working memory where subjects had to memorize the location of a dot within a circle and then use a pen to draw the dot in an empty circle, Huttenlocher et al (1991) observed a systematic directional error toward the oblique directions and away from the cardinal directions in a reference frame originating at the center of the circle. We observed a similar systematic directional error for movement end points when subjects made fast movements to the location of previously seen targets located in the periphery of an imaginary circle in a center out task (Smyrnis et al 2000;Gourtzelidis et al 2001), and de Graaf et al (1991, 1994 observed a comparable error in the initial heading direction when moving slowly or pointing toward a visual target in a similar center out task. Krukowski and Stone (2005) observed the systematic directional error in the heading of smooth eye pursuit, and Koehn et al (2008) observed the corresponding error pattern for antisaccade end points using the same reference frame.…”

Rotation and direction judgment from visual images head-slaved in two and three degrees-of-freedom

“…Similarly, related errors have also been observed for hand pointing to visually acquired azimuth target [14], [16], [23]. A model-based interpretation of the direction misjudgments in this and the prior studies in [20] and [21] will be reported elsewhere.…”

“…Open-loop response errors, such as those reported here, however, can be diminished by improving visual or kinesthetic feedback from the virtual or remote environment pointing task (e.g., [23]). This feedback may aid in correcting rotational misjudgments induced by inaccurate tracking and rendering of the operator's head roll angle.…”

Is the Curvature in Hand Movements to Haptic Targets in the Mid Sagittal Plane Caused by a Misjudgment in Direction?

“…The origin of such curvature has been explained in many ways, for example by the biomechanics of the arm [1], a perceptual distortion of space [2,3,4], or a misjudgment in direction [5,6,7].…”

“…In a study by de Graaf et al [5] participants made movements in a horizontal plane from a start position towards visually presented targets, and set the orientation of a pointer at the same start position to point towards the targets. These authors found that the initial direction of the movement deviated systematically from a straight line, and that a similar pattern of errors was made in setting the pointer.…”