This means that there does not exist any primary isolation between the different senses. The isolation is secondary. We perceive and we may with some difficulty decide thatone part of the perception is based upon the optic impressions. The synaesthetia is therefore a normal situation. The isolated sensation is the product of an analysis. In the scheme of the body, tactile, kinaedthetic and optic impulses can only be separated from each other by artificial methods.
What we have studied is the change in the unity of the postural model of the body by change in the sensation of the tactile and optic sphere. The nervous system acts as a unit accoding to the total situation. The unit of perception is the object which presents itself through the senses and through all the senses. Perception is synaesthetic.
(Schilder 1978: 38-39)
From Elizabeth Grosz's Volatile Bodies.