Visual discrimination of size and form in the albino rat / by K.S. Lashley.

  • Lashley, K. S. (Karl Lashley), 1890-1958.
Date:
[1912]
Catalogue details

Licence: In copyright

Credit: Visual discrimination of size and form in the albino rat / by K.S. Lashley. Source: Wellcome Collection.

Provider: This material has been provided by The Royal College of Surgeons of England. The original may be consulted at The Royal College of Surgeons of England.

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    The responses to sudden changes in the form of the stimuli are of importance as evidence of discriminating ability. Rat No. 6 was choosing the larger of two circles accurately (100%). Two squares of the same area, respectively, as the circles, were substituted for the circles and during the next io trials No. 6 was greatly disturbed, runnipg in and out of the starting box, creeping a little way down the passages, then turning back. She attended to the squares as to something new. There had been no noise to account for this behavior and it is not probable that the new forms had any peculiar odor, so it seems that the rat must have been disturbed by the change of form. This is only one instance of a type of behavior which appeared, to a greater or less extent, throughout all the experiments when- ever the form of the stimuli was changed. It suggests that the animals perceived the difference, although they never associated it with the motive, and raises the question whether the discrim- ination method offers a fair test of the animal’s discriminative ability. SUMMARY OF RESULTS In all the records there is a constant deviation in the per- centage of error, and a series of 20 successive correct trials is very rare. Sudden increases in the number of mistakes may frequently be explained by the physical condition of the animals. If they are fed too much or too little, their attention to the stimuli is affected and the percentage of error increases. When punishment is used, the rat’s fear of the punishment grill after too severe a shock causes irregularities in the records. Making allowance for such deviations, the selection of the vertical line 164 times in 200 trials (experiment 5) proves that rat No. 5 could distinguish between the vertical and horizontal lines. In discrimination of size, the record of only 14 mistakes in 150 trials shows that rat No. 4 could discriminate between the 30 and 50 millimetre circles. The number of animals used in the experiments has been small, necessarily, since the time required for each series is considerable. The rats show marked individual differences and all vary from day to day in their attention to the problem. The quantitative results are therefore only approximate. The tests for the threshold of form discrimination have been carried scarcely far enough to give definite results, and the data at
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