Pigeons in two experiments were first trained with a set of simple discriminations of the form AX+ CX-, BY+ DY- where A, B, C, and D were relevant, and belonged to one dimension, and X and Y were irrelevant and belonged to a different dimension. They were then tested with a discrimination of the form AX+ AY- BX-. The experiments revealed that the discrimination between AX+ and BX- was acquired more readily than between AX+ and AY-, which indicates that the original training resulted in the associability of the relevant stimuli being greater than that of the irrelevant stimuli. Experiment 2 revealed that the status of other stimuli from the two dimensions influenced these changes in associability. The associability of X and Y was enhanced by making other stimuli from the same dimension relevant, and the associability of A and B was reduced by making other stimuli from the same dimension irrelevant. The associability of the stimuli is attributed to the attention they are paid.