A coordinate system for the synthesis of visual and kinesthetic information

The results of this study suggest that information derived from kinesthetic inputs alone is not normally used to generate an estimate of the location of the hand in extrapersonal space. This finding provides support for the interpretation of previous results suggesting that a representation of a visual target in extrapersonal space must be transformed into a kinesthetic reference frame before the parameters of a targeted arm movement can be computed (Soechting and Flanders, 1989b). We asked subjects to use a pointer to indicate the spatial location of their hand following an unseen passive displacement. We found that subjects had large errors in the locations that they chose and that there was a large degree of variability for repeated trials with the same hand location. The errors were a result neither of using the pointer to indicate a spatial locus nor of an inability to make use of kinesthetic information. Instead, the errors resulted from an inability of subjects to synthesize an estimate of the hand's spatial location from only kinesthetic cues. We also asked subjects to use the pointer to indicate the location of their hand following a passive displacement when they had visual information about the passive displacement. In this case, we found that subjects performed better than when they had only kinesthetic information, but not as well as when they had only visual information about target location. This finding suggests that kinesthetic information about target location affects the processing of visual information.