Illusions : a psychological study.

  • Sully, James, 1842-1923.
Date:
1905
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Licence: In copyright

Credit: Illusions : a psychological study. Source: Wellcome Collection.

Provider: This material has been provided by UCL Library Services. The original may be consulted at UCL (University College London)

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    perception becomes evanescent. At other times the same impression will fail for an appreciable interval to divulge its meaning. These differences are, no doubt, due in part to variations in the state of attention at the moment; but they depend as well on fluctua- tions in the degree of the mind's readiness to look at the impression in the required way. In order to complete this slight analysis of percep- tion, we must look for a moment at its physical side, that is to say, at the nervous actions which are known or supposed with some degree of probability to accom- pany it. The production of the sensation is known to depend on a certain external process, namely, the action of some stimulus, as light, on the sense-organ, which stimulus has its point of departure in the object, such as it is conceived by physical science. The sensation arises when the nervous process is transmitted through the nerves to the conscious centre, often spoken of as the sensorium, the exact seat of which is still a matter of some debate. The intensification of the sensation by the reaction of attention is supposed to depend on some reinforce- ment of the nervous excitation in the sensory centre proceeding from the motor regions, which are hypo- thetically regarded as the centre of attention.1 The classification of the impression, again, is pretty certainly correlated with the physical fact that the central ex- citation calls into activity elements which have already been excited in the same way. The nervous counterpart of the final stage of per- 1 See Wumlt, rhjsiologische Psychohgie, p. 723.