Rate of key pecking by pigeons subjected to response-independent procedures in which a stimulus on the response key preceded food presentation was investigated in eight experiments. Color and shape of the stimulus, duration of the stimulus, probability of food following the stimulus, duration of the intertrial interval, and duration of food presentation were varied separately and in combination. All variables studied, except color and shape of the stimulus, had a reliable effect on pecking rate, but some variables had stronger effects than others. Rapid key pecking may be obtained with a variety of responseindependent procedures, as well as by response-dependent reinforcement. The results of experiments in which food is both dependent on key pecking and correlated with stimulus conditions are not representative of simple operant effects. Key pecking is an ideal response for studying the simultaneous operation of response-reinforcer and stimulusreinforcer effects.

Egger and Miller (1962) hypothesized that the conditioned reinforcing value of stimuli depends on their information value. Egger and Miller and others have tested this hypothesis by comparing the conditioned reinforcing value of 81 and 82 following Sl-Sz-reward training. However, none of these experiments have controlled for differential generalization of conditioned reinforcement value from training to comparison tests. That is, the 81 cue pattern during the conditioned reinforcement tests has been very similar to the 81 cue pattern of training, while the training and test 82 cue patterns have been quite dissimilar. In Experiment 1, pigeons in a procedure unconfounded by differential generalization produced 82 reliably more frequently than 81, and pigeons in a confounded procedure produced 81 somewhat more frequently than 82. A significant groups X stimuli interaction was attributed to differential stimulus generalization from training to test for 81 and 82 in the confounded condition. In Experiment 2, pigeons in an unconfounded procedure again produced 82 reliably more frequently under a different testing procedure. The results are interpreted as demonstrating that, following Sl-Sz-food training trials, 82 is the more effective conditioned reinforcer in unconfounded conditions. A reconceptualization of the information hypothesis is shown to be consistent with these results.A pure tone is sounded before each of several deliveries of a food pellet to a hungry rat. Later, each time the rat presses a bar. the tone follows. The frequency of responding increases; barpressing is positively reinforced by the tone. This example illustrates the phenomenon of conditioned or secondary reinforcement. A previously neutral stimulus, by virtue of having been followed by a reward (e.g., food), acquires the capacity to positively reinforce antecedent responses; the stimulus has become a positive conditioned reinforcer. Miller's (1962, 1963;Miller, 1961) information hypothesis is an attempt to specify the conditions under which reinforcement occurs and previously neutral stimuli acquire reinforcing properties. Egger and Miller (1963) hypothesized that "reinforcement occurs primarily at the point at which information is delivered .... Indeed, the arrival of information about primary reward may be the only occasion when reinforcement occurs" (p. 132). Egger and Miller (1962) defined "information" with respect to the procedures outlined in Figure 1. The S2 redundant and S2 informative procedures This article is based on a portion of a dissertation submitted to Kansas State University in partial fulfillment of the requirements for the PhD degree. The author wishes to thank his committee for their cooperation and most especially Charles C. Perkins for his persistent encouragement. The research reported was supported by NSF Grant DB 27595 and NIMH Training Grant 5TOIMH 08359 awarded to Kansas State University. Reprint requests should be sent to the author at the Department of Psychology, Northwest Missouri State University, Maryvil...

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