The Internal Senses — Functions or Powers? Part II

J. A. Gasson

Abstract

We will now try to show that the internal senses have definite brain structures as sensoria and that a correlation of what our psychological analysis has shown about these senses with the knowledge derived from the results of neurological research can help us better to understand the functioning of the inner senses and also the functioning of the brain. The brain functions outlined here were arrived at by an extensive study of the available very recent research evidence. While we are presenting a theory of brain function, it is the only one available that integrates the reported facts in a consistent way. Indeed, it is the only theory available today. We will show that it fits in well with the traditional teaching of philosophy on the internal senses, which may be an additional reason for saying that it fits all known facts.

According to St. Thomas, the sensus communis is a sensory power that has as its formal object the activity and content of the external senses. Now let us see what the sequence is that starts from the external senses and ends with the act of seeing objects. First, the sensory receptors are acted on by specific energies possessed by sense objects. This action has psychological as well as physical and physiological effects. For instance, light produces an optical image of the viewed object on the retina. The retinal cells react with action currents that travel along the optic nerve to the optic tract and the lateral geniculate bodies, the thalamic relay station for visual impulses. From there, relays go to the afferent plexus, one of six cortical layers in the visual area.

Normally, the physiological activity up to this point disposes the visual sense to see. This disposition, the psychological effect of visual stimulation, is the visual species impressa. The act to which it disposes the visual sense is the actual visual sensation. If the physiological process stopped at this point, there would be an experience of light and color, but not of seeing things as we ordinarily know them. If we are to see objects, the afferent nerve impulses must connect with the cortical cells in the remaining five layers of the sensory area. All these cells form an intricate network in which every cell is connected with several other cells. When these connections function the sensus communis apparently begins to operate; the effect of its act is the experience of seeing a visual object.