CONDITIONAL DISCRIMINATION-LEARNING BY PIGEONS - THE ROLE OF SIMULTANEOUS VERSUS SUCCESSIVE STIMULUS PRESENTATIONS

A series of experiments investigated the development of a conditional discrimination involving a blue or red keylight and a subsequently presented vertical or horizontal line. Pigeons trained in a single reversal paradigm failed to learn the conditional task despite manipulations that assured continued attention to the colors by reinforcing responding to them and other manipulations that reduced both the short-term and long-term memory requirements inherent in the task. If the colors both preceded and overlapped the lines, the subjects learned a conditional discrimination, but it involved only the overlapping component of the color and the lines. The sequential conditional discrimination was acquired only when training involved frequent reversals. The difficulty of learning a sequential conditional discrimination, relative to a simultaneous one, presumably reflects the true hierarchical nature of the task; simultaneous conditional tasks are not necessarily hierarchical.