Retroactive interference in rats: Independent effects of time and similarity of the intervening event with respect to acquisition

Events occurring during the retention intervals for a 5-min delayed alternation task were used to investigate the factors that influence retroactive interference. Appetitive reinforcement in an E-maze was employed to train rats on the delayed alternation task consisting of a forced-choice (target event) trial followed by a free-choice (test) trial. Occasional probe trials added a potentially interfering event either at the beginning, middle, or end of the retention period. These events also varied in similarity to the target events, ranging from low similarity to the converse of the target event. Interference increased both with the interval between the target and intervening events and with the similarity between the converse of the target event and the intervening event; however, there was no tendency, significant or otherwise, towards an interaction between stimulus similarity and the interval between the target and intervening events. Control groups demonstrated that the interference was of an associative nature and that the interval between the intervening event and the test trial was little consequence. These results are discussed in terms of two separate types of interference: similarity interference which depends on stimulus similarity of the intervening event to the converse of the target event but not on the temporal location of the intervening event, and processing interference which depends on the temporal location of the intervening event but not on its similarity to the converse of the target event.     

Prevention of the degraded-contingency effect by signalling training trials

Presentation of unsignalled unconditioned stimuli (USs) interspersed among Pavlovian excitatory conditioning trials weakens conditioned responding to a target conditioned stimulus (CS; Rescorla, 1968). However, signalling these intertrial USs with another cue (a cover stimulus) has been shown to alleviate this degraded-contingency effect (e.g. Durlach, 1982, 1983). In contrast to signalling the inter-trial USs, the present experiments examined the effect on the degraded-contingency effect of signalling the target CS-US pairings. Experiment 1, using parameters selected to avoid overshadowing, found that consistently presenting a cover stimulus immediately prior to the target CS-US pairings during degraded-contingency training alleviated the degraded-contingency effect. Experiment 2 examined the underlying mechanism responsible for this cover-stimulus effect through posttraining associative inflation of the cover stimulus or the context, and found that inflation of the cover stimulus attenuated responding to the target CS (i.e. empirical retrospective revaluation). The results are discussed in terms of various acquisition- and expression-focused models of acquired responding.     

Competition Between Outcomes

In both Pavlovian conditioning and human causal judgment, competition between cues is well known to occur when multiple cues are presented in compound and followed by an outcome. More questionable is the occurrence of competition between outcomes when a single cue is followed by multiple outcomes presented in compound. In the experiment reported here, we demonstrated blocking (a type of stimulus competition) between outcomes. When the cue predicted one outcome, its ability to predict a second outcome that was presented in compound with the first outcome was reduced. The procedure minimized the likelihood that the observed competition between outcomes arose from selective attention. The competition between outcomes that we observed is problematic for contemporary theories of learning.     

The community psychologist as social planner

The environmental movement may provide a vehicle by which community psychologists can contribute to large-scale ecological change. This paper uses one outgrowth of the environmental movement--the environmental impact assessment process--to illustrate the procedures for input by community psychologists can participate in the environmental impact assessment process to (1) predict the effects of any new project on the demand for treatment services and (2) suggest ways in which a project may be designed to prevent psychological problems and enhance community well-being.