Three pigeons were trained on the matching-to-sample task with 12-mm form stimuli (a circle, a triangle, and a cross). After 105 acquisition sessions, the fo1m stimuli were reduced in size to 8 mm for 65 sessions and then to 5 mm for 80 sessions. Durin~the next phase, the samples were 12 mm in size and the comparison stimuli were 8-mm forms, pr vice versa, 8-mm samples and 12-mmcomparison stimuli. Finally, the samples and comparison stimuli were presented as growing (increasing from 5 to 12 mm) or shrinking (decreasing from 12 to 5 mm) forms. The birds learned to match the three different sizes offorms and matched well even when the sample and comparison stimuli were not the same size. They could not match samples only on the basis of direction of size change.The simultaneous matching-to-sample (MTS) procedure has frequently been employed to assess conditional discrimination capabilities in nonhumans (e.g ., Cumming & Berryman, 1965;Ferster & Appel, 1961;Zimmerman & Ferster, 1963). At trial onset, a pigeon is presented with a sample stimulus projected onto the center key of a threekey response panel. A peck on the sample key produces a comparison stimulus (CO) on each of the two side keys. With all three keys now lighted, the bird's task is to peck the CO key presenting a stimulus that matches the sample. A peck on the matching CO key produces a reinforcer and the next trial. Mismatches are not reinforced. This study attempted to teach pigeons to (l) match form stimuli (a circle, a cross, and a triangle), (2) sustain matching levels regardless of the size of the samples and CO stimuli, and (3) match samples based on the direction of the size change .Several reports have indicated that it is more difficult to establish matching sample forms than hue stimuli (e.g. , Cumming & Berryman, 1965;Farthing & Opuda, 1974). In order to make the conditional discriminations as easy as possible, we employed the simultaneous MTS paradigm rather than the zero-delay MTS procedure. We also required that a fixed-ratio schedule be satisfied on the sample key before the CO stimuli were presented. Several papers have indicated that matching accuracy improves when ratio schedules are paired with the sample stimuli (Lydersen, Perkins, & Chairez, 1977;Roberts & Grant, 1976;Sacks , Kamil, & Mack, 1972). METHOD SubjectsThree whiteCarneauxpigeons, maintained at 80%± 15 g of theirfree-This studywas supported by a faculty research grant to the firstauthor. We would like to thank David Gough, Tim Lesneski, Lee Goodfellow, and Richard Cross for their assistance with data collection. Reprints may be obtained from Richard Pisacreta, Department of Psychology, Ferris State College, Big Rapids, Ml 49307. feeding weights, were used. The pigeons had been previously trained to matchfigure stimulibut had not been previouslyexposedto the form stimuli employed in this study. ApparatusThe apparatus was a 35 x 35 x 37 em operant chamber enclosed in a sound-attenuating hull. The response panel, 37 x 35 em, had nine 2.7-cm (BRS/LVEModel 121-16) response keys...

Two pigeons were trained on a six-key modified oddity-from-sample procedure. The stimuli were color pictures of birds, butterflies, and human faces. Initially, the third peck on the sample key (which presented one of three different bird pictures) lit only one comparison key. Every three additional pecks on the sample illuminated another comparison key. Fifteen sample pecks produced the maximum of five comparison stimuli. A peck on the comparison key that presented the nonmatching bird picture produced grain. Pecks on matching keys turned off all the comparison keys and repeated the trial. The birds learned to peck each sample until the nonmatching comparison stimulus was produced, and then to peck that key. After acquisition (70%-90% accuracy), the three bird stimuli were replaced by a new set of three bird pictures. Subsequent phases provided new sets of bird, butterfly, and human face stimuli. Both birds showed transfer of oddity learning to the novel samples. The data suggest that the birds may have been engaging in conceptualtype oddity learning, rather than learning discrete five-key discriminations or a series of two component chains.

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