Hand-centred coding of target location in visuo-spatial working memory

The aim of the present experiment was to determine the frame of reference u sed to encode a visually specified target location, in a simple, visuo-spat ial short-term-memory task, using delayed manual pointing. Subjects were re quired to remember the location of a single, visually presented stimulus, o ver delays of 3 and 30 s, and to recall its location by pointing to it with the tip of a stylus with eyes closed. There were two starting positions fo r the hand: one near the body, proximal to the target area, the other far f rom the body, i.e., beyond the target area. Two groups of twelve subjects p articipated in the experiment. One group observed the target locations in t he light, the other group observed the target LEDs in the dark. The results showed a large (between 10-30%) and consistent undershoot of the remembere d target location with respect to the hand's starting position, in the sagi ttal axis, both when the hand started from the near and from the far positi on. That is, from the far starting position, pointing errors lay consistent ly beyond the actual target location as seen from the subject's viewpoint. Further, this undershoot error in the remembered target location increased over time delay. These results are in favour of the hypothesis that the vis ual target locations were encoded in a hand-centred frame of reference in s patial short-term memory. They also implicate the use of motor- or action-r elated representations in visuo-spatial working memory. (C) 1999 Elsevier S cience Ltd. All rights reserved.