The After-Effect of Seen Movement When the Whole Visual Field Is Filled by a Moving Stimulus

Abstract

In his study of the after-effect of seen movement A. Wohlgemuth reports series of 34 experiments whose results he uses disprove current theories and support his own theoretical construction.1 One of these experiments, the 22d, is devised to ascertain how the after-effect is affected if the whole visual field is filled by an objective movement. The outcome is negative: there is a total absence of any after-effect. Wohlgemuth, apparently dissatisfied with this finding, repeats the experiment, with identical result. He accordingly concludes that after-effect is produced by an objective movement occupying the whole visual field.2 Later, his theoretical sections, he reviews and rejects all current theories for priori reasons or on account of incompatibility with experimental evidence, and proceeds, on the basis of McDougall's theory of drainage, the construction of theory which shall be in harmony with the ascertained facts.3 But relating this theory the facts he fails consider the results of his own Experiment 22.4 Yet these results, if they stand, appear contradict the theory, according which the phenomenon is no way conditioned upon size or spread of the stimulus but is wholly dependent on priority of entry and the consequent decrease of synaptic resistance. If the after-effect fails appear when the whole field is stimulated, the theory must either be discarded or radically revised. We hold no brief for the theory; but we were not either convinced by the outcome of the critical experiment, which we therefore decided repeat. We hoped also, by extending the method, by requiring introspective reports of process as well as statements of meaning, and by improving the apparatus and technique, contribute something toward complete phenomenology of the illusion. Observers.-We had two groups of O's. The members of the first group were Mr. W. A. Andrews (A), and Mr. S. Takaki (T), graduate students psychology; Mrs. I. G. Whitchurch (W), graduate scholar psychology; Dr. F. L. Dimmick (Di), assistant psychology; and Dr. K. M. Dallenbach (Da), instructor psychology. We gave these O's preliminary practice-series that should bring them