[not on handout, see intranet]
[pages 291-3 of Walker, 1987]
1) Morgan, M.J., Fitch, M.D., Holman, J.G. and Lea, S.E.G. (1976) Pigeons learn the concept of an ‘A’. Perception, 5, 57-66.
Abstract. Pigeons learned to discriminate between ‘A’s and ‘2’s in eighteen different typefaces. They subsequently showed excellent transfer to twenty-two typefaces that they had not previously seen; one pigeon was tested with handwritten letters and responded correctly to them also. Pigeon’s responses to ‘A’s and ‘2’s with parts removed suggested that their performance was controlled by several features, none of which could be considered necessary and sufficient. A test in which birds were shown other letters of the alphabet supported this conclusion. It appears that the original discrimination was learned as what Ryle calls a ‘polymorphous concept’.
Conclusion. As stated in the abstract, the data suggest that the birds learned about several different features of ‘A’s and ‘2’s in parallel. A related theory is that of “recognition by components” (Biederman, 1987), supported by Van Hamme et al (1992) and Kirkpatrick-Steger et al (1998).
2) Blough, D.S. (1985) Discrimination of letters and random dot paterns by pigeons and humans. Journal of Experimental Psychology: Animal Behaviour Processes, 11, 261-80.
Blough trained pigeons to discriminate between pairs of letter stimuli presented as computed- generated fonts on a video monitor. Each letter was paired with all other letters in turn with 4 days of trainingg on each pair. The data is present as a hierarchical tree based on errors, showing which letters were most likely to be confused with other letters. Not surprisingly letters which have features in common, such as M, N and W, or D, O and Q, are more likely to be confused, both by humans and by pigeons.