Distribution of trials and the partial reinforcement effect after minimal acquisition

Both Frustration Theory and Sequential Effects Theory appear to account with some plausibility for the Partial Reinforcement Effect (PRE) and accompanying phenomena. On the basis of Frustration Theory, however, a PRE should not occur after only minimal acquisition training. On this point, the experimental evidence is conflicting. On the basis of analogous studies employing extended acquisition, trial distribution may be suggested as a factor, among others, which might affect the occurrence of the PRE. All previous studies showing evidence for a PRE after minimal acquisition employed intertrial intervals (ITI's) in acquisition and extinction of no more than 15 minutes. The problem which this study was concerned with was therefore whether a PRE could be obtained after only minimal acquisition when trials were distributed. Accordingly, it was hypothesized that a PRE would occur after a sequence of only five trials under a partial reinforcement (PRF) schedule in an 'RNRNR' sequence, compared with performance following continuous reinforcement (CRF), irrespective of whether trials were highly distributed or highly massed. A factorial 2x2 design was used in which four groups of Ss were trained under two conditions of reward schedule (PRF or CRF), and two conditions of ITI both in acquisition and extinction. The method, apparatus and procedure of a previous study (McCain, 1969) which showed evidence for a PRE after only minimal acquisition were replicated as far as possible, except for changes required by the design or on theoretical grounds. Evidence was found for a PRE under both conditions of ITI in terms of differences in extinction trends, confirming the hypothesis tested. Trial distribution was found to effect the mean running speeds shown by PRF and CRF groups such that greater resistance to extinction was shown by the PRF group in comparison to the CRF group when the ITI was 30 sec., while running measures did not show this effect when the ITI was 24 hours. This latter lack of a significant difference appeared to be mainly due to a reduction in PRF running speeds when the ITI was 24 hours rather than an increase in CRF running speeds.Arts, Faculty ofPsychology, Department ofGraduat