The differential reinforcement of reward-produced and response-produced stimuli

In two experiments, groups received successive large-reward trials on odd-numbered days and successive small-reward trials on even-numbered days in the same gray alleyway. This produced a discrimination problem in which the memory of large reward (S^L) was reliably discriminative of large reward and the memory of small reward (S^S) was reliably discriminative of small reward. Intertrial interval (ITI) was varied both between and within groups. In the within-groups manipulation, ITI separating S+ trials differed from that separating S- trials. Experimental groups learned the discrimination, running slower to S^S (S- cue) than to S^L (S+ cue), and showed a negative contrast effect, running slower to S- than a small-reward control group. Discrimination was somewhat faster at massed than at spaced trials. The within-groups manipulation of ITI suggested that the effects of ITI were mediated by time-dependent changes in internal cues produced by reward events and by the instrumental response. The control exercised by internal cues was shown to be associative rather than nonassociative, e.g., motivational. Similarities with, and implications for, conventional brightness differential conditioning were discussed.     

Blocking in successive differential conditioning: Prior acquisition of control by internal cues blocks the acquisition of control by brightness

In each of four experiments the acquisition of discriminative stimulus control by brightness cues (black vs white runway) in a successive go/no-go instrumental discrimination was blocked in groups given prior discrimination training with internal (reward-produced and intertrial interval-related) cues as relevant discriminanda and brightness cues irrelevant. The blocking effects obtained here in instrumental conditioning were substantial and in most cases complete. Blocking occurred whether brightness in Phase I varied across trials but was uncorrelated with reinforcement (varied-irrelevant, V-I, condition) or whether all Phase 1 trials occurred to a single value on the brightness dimension (constant-irrelevant, C-I, condition) which then served as a redundant S+ cue in Phase 2 while the previously unexperienced brightness cue was added to the S- stimulus compound, or vice versa. Blocking in the V-I condition was shown not to be due simply to nondifferential reinforcement of brightness in Phase 1, but to depend on the prior acquisition of discriminative stimulus control by internal cues. As in Pavlovian conditioning, blocking here was an increasing function of amount of prior conditioning to the blocking stimulus. The results encourage the prospect that the procedures used here can be developed into a viable instrumental conditioning companion to the Pavlovian procedures now used almost exclusively to study blocking.     

Sequential effects on discrimination reversal

In Experiment 1 the sequence of trials to the positive (S+) and negative (S?) discriminanda was varied between groups during acquisition and reversal of a successive brightness discrimination. In Experiments 2 and 3, groups received different reward sequences in Phase 1 within S+. In general, groups given transitions from nonrewarded trials to rewarded trials (N-R transitions) in Phase 1 learned both the original discrimination and its reversal more slowly than groups given schedules devoid of N-R transitions. The results were discussed in relation to previously reported effects of partial reinforcement on acquisition and reversal of a discrimination and the role of sequential variables and internal, reward-produced cues in discrimination learning, reversal learning, and nonreversal shifts.     

Intertrial interval effects on internal stimulus control of behavior in brightness differential conditioning

In Experiment 1, groups were given a trial sequence in differential conditioning in which all S+ trials preceded all S? trials (+? schedule) or one in which some S+ trials followed S? trials (+?+ schedule) and either a 1- or a 30-min intertrial interval (ITI). ITI affected discrimination learning only in the +? schedule condition; schedule affected discrimination only at massed trials. In Experiment.2, all groups received a +?+ schedule. In two groups, given a 1- or 15-min ITI between all trials, discrimination learning was independent of ITI. Discrimination learning was facilitated in two other groups given a 1-min ITI between all trials except between S? and the subsequent S+ trial, when the ITI was either 15 or 60 min. The results were discussed in terms of their implications for internal reward-related stimulus control of behavior in differential conditioning.     

Practice and incentive motivation in recognition of inverted faces

In each of three experiments, participants received successive daily practice sessions on the task of recognizing inverted faces. In all practice sessions, an initial study series of 25 inverted faces was followed immediately by a test series of 17 pairs of inverted faces. Each test pair comprised a face from the study series and a new face. Completely new sets of faces were used in each session. Recognition of inverted faces did not improve across sessions in Exp. 1 but did improve in Exps. 2 and 3. Unlike Exp. 1, Exps. 2 and 3 employed an explicit incentive for improved performance. These results show that sufficiently motivated participants can become quite proficient at recognizing inverted faces. Implications of the results for the role of expertise at recognition in producing the inversion effect are discussed.