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Sixteen rats were trained to discriminate between a square and a rectangle: both shapes were presented in different orientations to different animals. All animals were trained in succession with positive shape only, positive and negative shapes presented simultaneously, positive and negative shapes presented successively; finally they were given tests with 18 transfer shapes presented singly. Although the rats showed a strong preference for the square early in training, they later responded more accurately to the rectangle presented on its own than to the square. There was no tendency to transfer from a rectangle in one orientation to rectangles in other orientations, and indeed when a horizontal rectangle was substituted for a vertical or vice versa negative transfer resulted. The rats (unlike octopuses) showed complete transfer to outline shapes. The transfer test results are discussed in relation to recent physiological discoveries about retinal receptive fields. [ABSTRACT FROM AUTHOR]

Octopuses were trained to discriminate visually between different pairs of mirror image shapes. The successive method of discrimination training was used. It was found first that octopuses discriminate more readily between up-down mirror images than between left-right mirror images; secondly, that octopuses discriminate as readily between mirror image shapes as between non-mirror image shapes of equivalent complexity. It was also shown that it is possible to train octopuses on a comparatively difficult discrimination by the method of making reward conditional upon an attack upon the positive shape presented upon its own instead of presenting reward with the positive shape every positive trial. Although initial learning by the former method is slower, a smoother learning curve is obtained by this method, and the final level of performance reached is higher. [ABSTRACT FROM AUTHOR]

Recent research on visual discrimination has largely ignored one of major problems in this field, namely what are properties of shapes to which animals are responding when they discriminate them: a solution to this problem must precede attempts to arrive at mechanism behind shape discrimination. Experiments were conducted on discrimination of orientation by octopuses. It was shown that discrimination of orientation was easy where orientations to be discriminated fall in vertical and horizontal directions, extremely difficult where orientations are midway between vertical and horizontal directions. Various transfer and memory tests were carried out which confirm that animals were discriminating orientation and not other properties of figures. A tentative explanation of results is proposed. An analysis of serial effects is attempted which suggests a possible interpretation of some of Boycott & Young's findings on effects of lesions to verticalis lobe in octopus. [ABSTRACT FROM AUTHOR]