The psychology of visual motion / by Henry J. Watt.

  • Henry J. Watt
Date:
1913
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Licence: In copyright

Credit: The psychology of visual motion / by Henry J. Watt. Source: Wellcome Collection.

Provider: This material has been provided by The University of Glasgow Library. The original may be consulted at The University of Glasgow Library.

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    And without systematization there can be no theory of the evolution either of the brain or of experience. (b) Adopting an opposite point of inquiry, we may now ask: What insight justifies the confidence with which a physiological theory of certain facts is offered and admitted? When double contacts give single touch, anyone apparently may understand that that is explicable only by a theory which assumes the existence of a single point of maximum central excitation and explains the way in which that arises out of the given double peripheral excitations. When an after-effect of negative sign arises from preceding objective movement, or when a movement arises from one or more resting stimulations, anyone may likewise understand that no laws of mind lie hidden here. The assumption of an indubitable parallelism of mind and body seems to be the only justification of these views. But this assumption, as we have seen, is abandoned by Wohlgemuth in his special physiological theory of motion and its after-effect. Why should we, then, retain it at all? Why not maintain that, when single touch results from double contacts, both the central and the peripheral excitations are double, and that single touch is due to the fact that for the two excitations the soul has rendered only one experience? Alternatively we might assume that the two excitations really did arouse two sensations, but that these two fused for some reason into one. Such assumptions have indeed been made, not perhaps for double contacts, but for those binocular stimulations which result in single fused vision. And no charge of absurdity or of obvious error could be brought against them. But these two cases of single touch and single vision from double stimulations are essenti- ally parallel in nature. For the former only physiological explanations are generally admitted; for the latter physiological reasons have also been given, but they have been held to be utterly inadequate and psychological interpretations have been favoured instead1. If the physio- logical or the psychological line of explanation is preferable in special cases, there must surely be clear ground for the preference. This ground seems to me to be a tacit recognition of the possibility and validity of pure psychological theory. In dealing with single touch or any other similar sensations, we recognise that there is nothing psychologically simpler and more primitive than elementary sensation itself to which we might appeal for an explanation of its characteristics. Consequently, if one class of sensations shews features which another does not possess, we feel justified in assuming that the anomaly must 1 Cf. W. McDougall, Body and Mind, London, 1911, chap. xxi.
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