Successive two-item same-different discrimination and concept learning by pigeons.

Four pigeons were trained in a successive same/different procedure involving the alternation of two stimuli per trial. Using a go/no-go procedure, two different or two identical color photographs were alternated, with a brief, dark, inter-stimulus interval, on a computer screen for 20s. Pigeons learned to discriminate between same (S+) and different (D-) sequences with moderate to large contrasts between successive pictures. Analyses of pecking behavior within single trials revealed this discrimination emerged at the earliest possible point in the sequence (i.e. by the presentation of the second item). Pigeons transferred to novel color and gray-scale pictures, and showed savings in tests with novel video stimuli. These results suggest that same/different discrimination and concept formation can be acquired with successively presented pairs of stimuli by pigeons. When combined with results using simultaneous same/different presentations, these findings further support a qualitative similarity among birds and primates in their capacity to judge certain types of stimulus relations.