Failure of visual prototype learning in the pigeon

Pigeons did not show generalization gradients along a distortion level after single stimulus training with dot patterns produced on a computer-controlled CRT. After discrimination training between a triangle made of six dots versus patterns made up of six random dots, the birds showed orderly generalization gradients as function of degree of distortion of the original triangle. When they were trained with distorted exemplars of the prototype triangle, they responded more often to triangles at this level of distortion than to the prototype triangle. This observation suggests a lack of abstraction of the prototype from its distorted samples. Such failure of prototype learning was also obtained after training with a different S? (a square made up of six dots) or with a different S+ (horizontally arranged dots).