The effect of stimulus position on visual discrimination by the rat.

Pattern vision in the rat bas been most effectively studied by a jumping method devised by Lashley (1930). This procedure requires the rat to jump at one of two cards bearing the patterns to be discriminated. On the basis of Laehley’s extensive anatomical and behavioural studies it has been assumed that the cards fall within the rat’s binocular field of vision and, consequently, that they are seen as a whole at the time when the visual patterns begin to influence behaviour during discrimination learning. Ehrenfreund (1948), however, thought that the rat’s effective field, in the Lashley jumping apparatus, might be limited to the lower margin of the cards, and has demonstrated this experimentally in certain conditions of training. Since Ehrenfreund’s data have been interpreted as bearing on the current continuity-noncontinuity controversy concerning the nature of learning, his experiment is of general importance. Ehrenfreund trained his rats on a modified Lashley jumping apparatus to discriminate between an upright and an inverted triangle in two differing experimental situations. In one condition, the triangles were raised eight centimetres above the bottom margin of the cards. The platform from which the rats jumped, as in the usual procedure, remained level with the platform on which they found food. In the second, the platform was also raised, so that the rats were jumping at the centre of the cards where the triangles were now located. [...