The visual or tactual activities for the shape perception consist of two phases; the “grasping” phase at the beginning stage, and the following “verifying” phase. The acquisition processes of the shape perception and the mutual division systems between the visual activities and the tactual activities were investigated in a congenitally blind boy (KM) after an operation was performed to restore sight. KM underwent an aspiration of both cataractous lenses at the age of 9. Before the operation, his ERG was normal. KM had already established the tactual systems for shape perception through out his blind life, and he had verbally retarded behavior. The experiment tasks were set up in order to form his visual functions of shape perception for a 2-dimensional triangle, circle, or square.
As KM’s visual scanning strategies by means of his head movement were performed, (1) the percent of correct responses gradually went up, and (2) gradually his tactual activities disappeared, although in the first stage KM grasped and verified the shape by means of his hands/fingers. The tactual systems were replaced by the visual systems in shape perception.