CONTIGUITY AND CONDITIONED REINFORCEMENT IN PROBABILISTIC CHOICE

In a baseline condition, pigeons chose between an alternative that alw ays provided food following a 30-s delay (100% reinforcement) and an a lternative that provided food half of the time and blackout half of th e time following 30-s delays (50% reinforcement). The different outcom es were signaled by different-colored keylights. On average, each alte rnative was chosen approximately equally often, replicating the findin g of suboptimal choice in probabilistic reinforcement procedures. The efficacy of the delay stimuli (keylights) as conditioned reinforcers w as assessed in other conditions by interposing a 5-s gap (keylights da rkened) between the choice response and one or more of the delay stimu li. The strength of conditioned reinforcement was measured by the decr ease in choice of an alternative when the alternative contained a gap. Preference for the 50% alternative decreased in conditions in which t he gap preceded either all delay stimuli, both delay stimuli for the 5 0% alternative, or the food stimulus for the 50% alternative, but pref erence was not consistently affected in conditions in which the gap pr eceded only the 100% delay stimulus or the blackout stimulus for the 5 0% alternative. These results support the notion that conditioned rein forcement underlies the finding of suboptimal preference in probabilis tic reinforcement procedures, and that the signal for food on the 50% reinforcement alternative functions as a stronger conditioned reinforc er than the signal for food on the 100% reinforcement alternative. In addition, the results fail to provide evidence that the signal for bla ckout functions as a conditioned punisher.