2003 Volume 10 Issue 2 Pages 244-257
We investigated quantitatively and systematically the integrative spatial representation of extrapersonal space in walking distance with reference to both body- and environment-centered coordinate systems. A target was presented at one of the five different locations in 2m ahead from subjects for 2sec. Subjects were required to remember the location of presented target, and after a delay of 3sec, to point to the remembered target location. Under the complete dark, pointing errors lay consistently in displaced locations toward the body position, the magnitude of which was shown as a linear function of the distance from subjects' body position to target. Given a specific allocentric visual cue, the frames of the target area, in both target presentation and recall, the errors decreased for any targets. Our findings of pointing error could be explained by the weighted sum of two types of pointing error on the assumption of probabilistic independency. One type of error was would occur in the transformation process solely from the egocentric spatial representation of target with reference to subjects' body and head directing to the front. The other was shown as displacement toward the nearer frame of target presentation area. This type of error would occur in the transformation solely of the allocentric representation with reference to the frames. These results suggested (1) that the quantitative characteristic of pointing solely on the allocentric spatial representation of targets which would not be isolate experimentally, could be estimated on the assumption of probabilistic independency of the behavioral characteristic solely on the egocentric spatial representation, and (2) that for both egocentric and the allocentiric spatial representation, the basic characteristic of pointing in walking distance was shown as the errors displaced toward the center of the spatial coordinate systems.
