Abstract
Spatially-directed behavior from perception to action is coded in supra-modal coordinate systems that integrate visual, tactile and proprioceptive information. To study the interactions between the visual and proprioceptive information on the estimation of the subjective sagittal midpoint, we performed a straight ahead pointing task, and compared to “with” and “without” visual information. Subjects stood or seated in front of a large sheet of paper (0.8 m × 1.1 m) that was recorded pointing locations. They had a leaser-pointer with left or right hand, and they were required to make free pointing towards the subjective midpoint. The distances between the locations where subjects pointed and the objective midpoint were measured. The pointing distance varied 3 m, 2 m (far-space) and 0.5 m (near-space). Without vision, when the pointing distance was far-space, the results showed that the subjective midpoints deviated to the left of the objective midpoint. No deviation was observed in near-space. The mean leftward deviation in far-space was 2.8 degrees (S.D. = 0.81) in visual angle. On the other hand, with vision, subjective midpoint was consistent with objective midpoint. The results showed two dissociations. One is that the body-center referred to the spatial encoding system with proprioception is dissociated from the center of the visual field. Second, our results conclude the dissociation between the near and far space. Previous studies discussed that there might be one set of spatial maps specialized for near and another for far-space in the human brain, our results are consistent with the hypothesis.