A comparison of intradimensional and extradimensional shift learning in pigeons.

In each of three experiments pigeons were trained on a simultaneous discrimination between stimuli that differed in both colour and orientation. For half the birds the colour dimension was relevant and for half orientation was relevant (i.e., differences along that dimension were correlated with reward and nonreward). All birds were then shifted to a second discrimination between new colours and orientations. For half this constituted an intradimensional shift in that the previously relevant dimension remained relevant; for the remainder the previously irrelevant dimension was made relevant (an extradimensional shift). Contrary to the predictions of attentional theory, the two types of shift were learned with equal ease.