Estímulo discriminativo de extin？？o produzido por respostas de observa？？o em pombos

food-deprived pigeons were given a series of trials in which half ended with response- independent food presentation and half without it. during a trial, pecking the key could change its color from white to green (s+) or red (s-), depending on whether food was programmed or not. in baseline conditions, pecks produced both stimuli (colors) on a 15-s variable-interval schedule. in two different conditions, tandem vi drh was applied to produce either s+ or s-. results showed that the tandem contingency resulted in a general decrease in the discriminative stimulus production, markedly to s+, but not to s-. the findings are consistent with the uncertainty-reduction model of conditioned reinforcement.