Attentional trade-offs in pigeons learning to discriminate newly relevant visual stimulus dimensions

Theories of selective attention posit that the amount of attention paid to some stimulus dimensions is inversely related to that paid to others, particularly under demanding task conditions. This ''inverse hypothesis" and the data that support it have long been controversial. We developed a new, attentionally demanding, stepwise discrimination task to test the inverse hypothesis. Eight pigeons discriminated among 16 visual stimuli consisting of all combinations of four binary dimensions: brightness (black/white), size (large/small), line orientation (vertical/horizontal), and shape (circle/square). Each of four consecutive training phases required attention to one additional, more difficult stimulus dimension. As discriminative dimensions were added, discrimination of previously learned dimensions temporarily worsened in five: of the: pigeons. We conclude that attending to new dimensions transiently reduced these pigeons' attention to previously learned dimensions. Of the three pigeons that did not show attentional trade-offs, two learned exceptionally quickly, suggesting that the inverse hypothesis predominately prevails under challenging circumstances. (C) 2001 Academic Press.