Transfer to intermediate forms following concept discrimination by pigeons: chimeras and morphs.
Pigeons treat blended pictures like smooth gradients, so probe with morphs to catch narrow stimulus control before it hardens.
01Research in Context
What this study did
Researchers taught pigeons to peck at pictures of cats and not dogs. They used clear photos first, then tested the birds with blended images called morphs and chimeras.
Each session gave grain for correct pecks and a short blackout for errors. The team tracked how the birds sorted the fuzzy in-between pictures.
What they found
The pigeons learned the cat vs dog rule in about five sessions. When shown morphs, they still picked the side that had more cat features.
Their choices followed smooth curves, not the sharp switches humans show. Small local cues like ear shape controlled more of the choice than the whole picture.
How this fits with other research
Sanders et al. (1989) saw the opposite result. Monkeys trained on same vs different failed when the pictures moved. The monkeys needed the exact static cues they first saw, while Natasha’s pigeons coped with blended stills. Species and stimulus type explain the clash.
Thompson et al. (1974) and BERRYMAELLIOTT et al. (1962) set the stage. They showed pigeons and rats give smooth generalization curves when one cue gets louder or brighter. Natasha et al. moved the idea to complex photos and still saw the same curves.
Cicchetti et al. (2014) later added that bigger differences between pictures speed pigeon learning. Together the studies say: pick clear examples first, then probe with small changes to map what the bird really sees.
Why it matters
When you teach a new discrimination, test with blended or partial examples early. If the learner starts to fail on morphs, you know they are hooked on a tiny detail, not the full concept. Shift the teaching set or add more varied photos until the curve flattens. This keeps stimulus control broad and prevents rigid errors in both kids and clients.
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Join Free →After the learner masters clear S-D vs S-delta photos, slip in three morphed images and record the choices to see if control is too narrow.
02At a glance
03Original abstract
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.
Journal of the experimental analysis of behavior, 2004 · doi:10.1901/jeab.2004.82-125