Experiment 1 demonstrated that reliably correlating different reinforcer locations (top vs. bottom) with sample stimuli markedly enhanced the performance of White Carneaux pigeons in a spatial conditional discrimination. This differential outcome effect was more evident at longer retention intervals. In Experiment 2, pigeons were given the opportunity to learn about two redundant reinforcer features--location (top vs. bottom) and quality (grain vs. chow). Which reinforcer feature exerted control over choosing depended on task structure. In the congruent task, where pecks to the top key operated the top feeder and pecks to the bottom key operated the bottom feeder, reinforcer location exerted predominant control. In the incongruent task, where pecks to the top key operated the bottom feeder and vice versa, reinforcer quality exerted exclusive control. These results have implications for the nature of reinforcer representations in instrumental learning.

Three groups of dogs were trained to perform one response (Ri) following one stimulus (St) and a second response (Ra) following a contrasting stimulus (82) in order to avoid electric-shock USs. For two experimental groups, Si consistently warned of US to one leg while S 2 consistently warned of US to the other leg; for the control group both Si and S 2 could be followed by shock to either leg. This choice-avoidance task was learned faster when the two stimuli each consistently signaled a different US than when there was no consistent relationship between the stimuli and the USs. Apparently, different types of shock USs condition discriminably different fears, and these fears provide cue stimuli which can facilitate the acquisition of appropriate choice behavior.

39 goldfish, either normal, sham operated, or forebrain ablated, were tested in the acquisition, extinction, and retention of an instrumental avoidance response with either a short or long delay between operations and testing. Forebrain removal severely impaired or prevented acquisition, greatly reduced resistance to extinction, and completely abolished a previously learned response. The deficits were permanent-an 8-wk. delay between operations and testing did not result in improved performances. Median escape latencies did not differ between groups, indicating that the deficit is specific to avoidance learning.

5s were exposed to inescapable traumatic shock. Then, either 24, 48, 72, or 144 hr. later they were given instrumental avoidance training using a technique which eliminated all escape contingencies. Short time intervals between inescapable shock and avoidance training produced severe interference with the acquisition of avoidance responding as compared with a control group.But at longer intervals the amount of interference decreased. These results imply that the interference phenomenon is not mediated by the concurrent presence of shock, as has been suggested.

When compounded with a cue for avoidance, a CS+, which had signaled impending shock during Pavlovian conditioning, increased avoidance responding, while a CS-, which had signaled a period free from shock, had the opposite effect. Evidence was derived from (a) comparisons of responding during compounds to responding during avoidance cue alone, and (6) comparisons of the experimental group's responding during compounds to responding during CS plus cue compounds by a control group for whom there had been no CS-shock contingency during Pavlovian conditioning. Rescorla and LoLordo (1965) have demonstrated that certain Pavlovian conditioning procedures produce stimuli which, when superimposed upon performance of a temporally paced unsignaled (Sidman) avoidance response, produce marked decrements in performance of that response, while yet other procedures result in stimuli which increase the rate of avoidance responding. These increases and decreases in avoidance responding, which were attributed, respectively, to the fear-inhibitory and fearexcitatory properties of the Pavlovian stimuli, were obtained by comparing rate of avoidance responding during the Pavlovian stimuli with rate of avoidance responding when no stimulus was present. The rates of responding during the experimental tones were not compared to rates of responding during appropriate control stimuli. Failing this, the possibility remains that one (but certainly not both) of these effects is due to inherent effects of novel stimuli on avoidance responding rather than upon a fear-controlling property given to the stimulus by the Pavlovian conditioning procedure. Comparison of rate of responding during the experimental tones with rates of responding during appropriate control stimuli could have provided further support for their interpretations.But what are the appropriate control stimuli with which one can contrast possible inhibitory or excitatory stimuli? Prokasy (1965) and Rescorla (1967) have analyzed and questioned traditional control procedures for Pavlovian conditioning. They concluded that the common procedures are not fully satisfactory because they result in stimuli which have some