Ghosh, N., Lea, S. E. G., & Noury, M. (2004).
Transfer to intermediate forms following concept discrimination by pigeons: Chimeras and morphs.
Journal of the Experimental Analysis of Behavior, 82, 125-141.
Two experiments examined pigeons’ generalization to intermediate forms following
training of concept discriminations. In Experiment 1, the training stimuli were sets
of images of dogs and cats, and the transfer stimuli were head/body chimeras, which
humans tend to categorize more readily in terms of the head part rather than the
body part. In Experiment 2, the training stimuli were sets of images of heads of
dogs and cats, and the intermediate stimuli were computer-generated morphs. In
both experiments, pigeons learned the concept discrimination quickly and generalized
with some decrement to novel instances of the categories. In both experiments,
transfer tests were carried out with intermediate forms generated from both familiar
and novel exemplars of the training sets. In Experiment 1, the pigeons’ transfer
performance, unlike that of human infants exposed to similar stimuli, was best
predicted by the body part of the stimulus when the chimeras were formed from
familiar exemplars. Spatial frequency analysis of the stimuli showed that the
body parts were richer in high spatial frequencies than the head parts, so these
data are consistent with the hypothesis that categorization is more dependent on
local stimulus features in pigeons than in humans. There was no corresponding
trend when the chimeras were formed from novel exemplars. In Experiment 2, when
morphs of training stimuli were used, response rates declined smoothly as the
proportion of the morph contributed by the positive stimulus fell, although
results with morphs of novel stimuli were again less orderly.
Key words: concept discrimination, global features, local features, spatial frequency,
generalization, key peck, pigeon