The time of perception as a measure of differences in sensations / by Vivian Allen Charles Henmon.

  • Henmon, Vivian Allen Charles (V. A. C.), 1877-
Date:
1906
Catalogue details

Licence: In copyright

Credit: The time of perception as a measure of differences in sensations / by Vivian Allen Charles Henmon. 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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    pression to this law by the assumption that the just noticeable differ- ence is a constant quantity, and, further, that what applies to finite or sensed differences applies also to infinitely small differences. This being assumed, Weber’s law becomes: the sensation varies as the logarithm of the stimulus, or, in other words, if sensations are to in- crease in an arithmetical ratio, the stimuli must increase in a geomet- rical ratio. These two assumptions have given rise to much controversy, which is by no means settled. It is argued by Fechner, Wundt and many others that it is a contradiction to assert that the just noticeable difference is not a constant. If the difference between sensations is just noticeable, it can not be more or less than this difference or it would not then be just noticeable. To which it is replied that this is a confusion of the difference in sensations with the sensation of being different, and that there is in consciousness no such thing as a differ- ence in sensations which can be obtained by the subtraction of the magnitude of one sensation from another. Moreover, experiments show that the just noticeable difference varies widely with different individuals and with the same individual at different times, with the different senses, with varying degrees of practise, etc. The second assumption leads necessarily to the assumption of negative sensations, which has likewise occasioned much debate. It is assumed by Fechner, Wundt and those who support Fechner’s law that the zero-point on the scale of sensations is the point of just noticeable difference. It is necessary to assume further, however, that there are differences in sensation below the threshold, and that these sensations, negative as contrasted with the positive sensations above the threshold, must also increase proportionally to the stimulus. This gives rise to many mathematical and other difficulties which will not be taken up here. Again, in his discussion of errors of observation. Professor CattelP says, concerning the just noticeable difference: “Another case in which German psychologists have run counter to the theory of prob- ability is in the assumption of a just noticeable difference. According to the theory of probability the apparent difference in sensation and the probability of correct judgment tend to increase continuously as the differences between the stimuli are made greater, but it is entirely arbitrary to choose one difference and call it just noticeable. A difference in the stimuli can be found which will be obscured by the error of observation 1 time in 10 or 1 time in 1,000, but no difference can be called just noticeable, meaning that it and larger differences will be correctly distinguished, while smaller differences will be in- distinguishable.” ^ J. McKeen Cattell, ‘On Errors of Observation,’ Am. Jour, of Psychol.,. 5: 284-293, 1893.