Perception is sometimes defined as “ the knowledge we obtain, by means of our sensations, of the qualities of matter.” This definition may be admitted, if matter is understood as including our own bodily organism, as well as the extra-organic objects to which it is related. The former is the only kind of matter that is immediately cognisable by the senses. The existence of a material world, distinct from, though related to, our organism is made known to us, not by the senses themselves, but, as will be noticed hereafter, by the faculty of locomotion.
Sensation and perception, as above explained, are always correlative to each other; every sensation being accompanied by a consciousness of the extension of the sensitive organism, and this consciousness being a perception. But, though always coexistent, they are not proportionally coexistent. On the contrary, the sensation, when it rises above a certain low degree of intensity, interferes with the perception of its relations, by concentrating the consciousness on its absolute affection alone.
Hence Sir William Hamilton, from whom the above remark is taken, has enunciated the important rule, that, above a certain point, the stronger the sensation, the weaker the perception; and the distincter the perception, the less obtrusive the sensation. In other words, though perception proper and sensation proper exist only as they coexist, in the degree or intensity of their existence they are always found in an inverse ratio to each other.
Sensation and perception, according to the above law, coexist, though in an inverse ratio to each other, in each of the five senses. But in addition to the relation which each bears to the other, when viewed with reference to the same sense, they are also found to be combined in different proportions when one sense is compared with another. In some the sensation so far predominates over the perception, that the sense manifests itself as a source of feeling rather than of knowledge, and has often, though erroneously, been regarded as consisting of the former element only.
In others the reverse is the case; the perceptive element, or cognition of an object, predominates over the sensitive element, or consciousness of a personal affection. In this point of view, the senses of smell and taste may be distinguished as especially subjective or sensational; those of hearing and sight as objective or perceptional.
Touch, inasmuch as it has no special organ, but is diffused in various degrees over the various parts of the body, will require a separate consideration. In other words, smell and taste are chiefly known as vehicles of the mental emotions of pleasure and pain; hearing and sight, as informing us of the nature of the bodily attributes of sound and colour. Touch may contribute to the one or the other end, according to the part of the body in which it resides, and the manner in which it is brought into exercise.
***Excerpt from Henry Longueville Mansel, B.d.. Metaphysics or the philosophy of consciousness