this paper, the posited competing behavior has been called hopper-observing behavior, as opposed to superstitous behavior (Skinner, 1948), in order to make the point that a dependent relation between eating and hopper detection exists even when hopper presentations are response independent. The behavior that emerges and persists is not specified by the experimenter, however, so idiosyncratic ... [Show full abstract] movements across pigeons, and modification of those movements in individual pigeons across time, are likely to occur. Some of these changes in behavior may be attributed to adventitious reinforcement in the sense in which Skinner (1948) intended the term. Others have suggested (Staddon & Simmelhag, 1971; Timberlake & Lucas, 1985) that these responses are elicited by the periodic presentation of food and therefore are species specific (the authors noted similarities between behavior produced by response -independent food and both begging for food in young squab and begging for food by female pigeons in courtship). Future studies may be aimed at parceling out the relative contributions of hopper-observing behavior, superstitious behavior, and species-specific behavior to the reduction in rates of key pecking produced by unsignaled delayed reinforcement. For now, we think the current experiments make it clear that dependent relations between behavior and eating (and between behavior and reinforcer-correlated stimuli) remain even when food reinforce- 122 DAVID W. SCHAAL et al.