Positive behavioural contrast : response suppression and the signalling of reinforcement

In two experiments the effects of a hitherto unused technique to suppress responding by pigeons in one comp­onent of a mult VI20 VI20 schedule were explored. This technique involved the presentation of a lighted bulb (called the stimulus-correlated-with-reinforcement, or SCR) which signalled the immediate availability of response produced reinforcement. Results were interpreted as offering no support to current hypotheses relating to necessary and sufficient conditions for observations of positive behavioural contrast. Further SCR experiments aimed at clarifying the need to postulate stimulus aversiveness and the function of inhibition in explanations for positive interactions, were outlined. These incorporate orthogonal dimensions for com­ponent discriminative stimuli and SCR, and shorter mean inter-reinforcement intervals. A variant of the SCR tech­nique by which brief presentations of the constant component discriminative stimulus constitutes the SCR, was suggested as a possible device for manipulating S2 response rate as an independent variable. It was concluded that the SCR technique appears to have a useful future in similar research because it minimally interferes with schedules and other conditions in the exp­ erimental chamber, and that an analysis of interaction effects may be possible in terms which exclude reference to inhibition and aversiveness, and refer solely to relat ive excitatory strengths of the stimuli used