The constructional disabilities are cognitive impairments that show difficulties in visually guided construction of spatial patterns (copying line drawings, block patterns and finger constructions). The cause of them is less well understood. To make clear it we investigated the behavioral characteristics of a brain injured subject who had difficulties in copying finger constructions. Video tape recording of the subject's finger copying revealed that he needed visual confirmation of his own hand. It implied that the difficulty came from the disturbance of the internal feedback system i.e., the forward model. To confirm it his mental manipulation ability of finger constructions and block patterns was investigated. The result showed that the subject had disturbance in the mental manipulation of the hand. Several studies suggested that the mental manipulation was executed by the mental models of external environment including own body. Forward model is the major component of these mental models. The result of our study suggested that the critical problem of the constructional disabilities was come from the forward model impairment. And this function was also suspected to be concerned with the left lateral parietal cortex.
