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Neurological Aspects of the Sense Powers of Man
- The Thomist: A Speculative Quarterly Review
- The Catholic University of America Press
- Volume 26, Number 1, January 1963
- pp. 35-66
- 10.1353/tho.1963.0034
- Article
- Additional Information
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NEUROLOGICAL ASPECTS OF THE SENSE POWERS OF MAN T HE philosophic interest in organic faculties usually extends only to the fact of organic involvement on the part of these faculties and the consequent conclusion that the material organic part forms a unified principle of operation in conjunction with its informing faculty/ The primary philosophic concern is with the nature and intrinsic intelligibility of this organic structure. The philosopher of human nature is generally content to establish the fact that the material organ and its informing faculty form a principium conjunctum operationis. Each faculty has its proper material organ-on the strictly philosophical level nothing further is called for.2 However, it is possible to fill out the picture in terms of specific structures from recent scientific contributions in neurophysiology. The argument cannot be presented in clear-cut terms for two reasons. First, the state of neurological evidence is by no means complete. Certain facts are almost immediately evident (relation of the eye to vision), but other facts are somewhat more tenuous and even highly controverted. Evidence related to vision and hearing has been well established for some time, but the evidence concerning taste, smell and touch, as well as the function of the internal senses has been more 1 St. Thomas' classic text is Summa, I, 77, 5. For a modern presentation of the argument, see G. P. Klubertanz, S.J., The Philosophy of Human Nature (New York: Appleton-Century-Crofts, 1958), pp. 116-118. 2 For a discussion of the aims and methods of the philosophy of human nature as contrasted with those of scientific psychology, see Klubertanz, ibid., pp. 885401 . A further discussion can be found in T. W. Guzie, S.J., The Analogy of Learning (New York: Sheed and Ward, 1960), pp. !'27-47. The distinctions are relevant to our investigation in terms of the relation of the philosophy of human nature to physiological psychology and particularly to neurophysiology and neuroanatomy . Another point of view can be found in .T. A. Weisheipl, 0. P., The Dignity of Science (Washington, D. C.: The Thomist Press, 1961), particularly pp. xxvi-xxix. 35 36 W. W. MEISSNER or less clarified only quite recently; consequently, the evidence is more tenuous in these latter areas. Second, even where the neurological £acts are clear-cut and unambiguous, there is still considerable room £or questioning their philosophical implications . The doctrine o£ specific nerve energies has been known since the early nineteenth century (1838) but it is still not clear whether the optic nerve is part o£ the organ o£ sight or whether the specific response to non-specific stimulation 3 is due to the specific nature o£ the visual center. I shall presume in this discussion that all those parts whose removal would interrupt a given £unction are component, integral parts o£ the organ in question. I shall concern myself here only with anatomical structures. Discussion o£ physiological £unction would take us too £ar afield and would involve too many highly disputed and technical issues. We shall attempt tentative reconstructions o£ the neurological circuits £or the external senses (sight, hearing, taste and touch), and the internal senses (common or unifying sense, memory or imagination, estimative sense, and memorative power). The designation o£ specific organs does not mean that the entire organ is actually involved in a given system . Usually there is question o£ particular cells groupings or particular fiber tracts, which form only part o£ the designated anatomical structure. Vision The optical system is quite well established. Light stimulus breaks down rhodopsin (visual purple) which is contained in the retinal neurons (rods) into retinene and protein. This photochemical change sets up an electrical impulse. Similar changes seem to occur in daylight vision through the breakdown o£ iodopsin (contained in the cones). The electrical impulse is carried £rom the rods and cones o£ the retina to a secondary layer o£ bipolar neurons in the retina. The bipolar 3 For example, pressure on the eye produces visual effects; consequently, the stimulus need not be specific-in this instance, color. NEUROLOGICAL ASPECTS OF SENSE POWERS OF MAN 37 neurons transfer the impulses to large ganglion cells whose axons collect at the blind spot of the retina and...