Memory decrement and proactive interference

We hypothesized that subjective expectations were responsible for the release from proactive interference (PI) rather than the actual change in taxonomic subcategories. The experimental conditions included informing or not informing subjects of the change in taxonomic subcategory, crossed with whether the taxonomic subcategory was actually changed or remained unchanged. The interest in whether a release would be seen when the subjects were informed of a change, yet no change was actually administered, was most specific. Significantly higher recall was found for the condition in which subjects were informed of a change, but no actual change occured (I-NC) than in the control condition in which subjects were neither informed of a change nor did one occure (NI-NC). The overal results indicated that control condtions revealed lower recall than other conditions, F(3, 129) = 2.96. p < . 05 on the critical trial. However, even when subjects were not told of a change, but a change occured (NI-C) a release from PI was observed, M=. 69. A release from PI may be induced by the subject's self-awareness of the change in taxonomic subcategory. Russ-Eft (1979) wrote that "proactive interference (PI) is a phenomenon characterized by a decreasing probability of recall with an increasing number of to-beremembered items" (p. 422). However, since the late 1970's, little has been done to further understand this concept. Nevertheless, we were interested in the phenomenon because of the importance it plays in diverse applications in society. For example, it may be that if the phenomenon of PI is understood better, we will be able to utilin. that knowledge when developing academic learning curricula, industrial training programs, and other procedural learning situations. It may be possible to make those learning experiences more fruitful by helping learners commit more information to long-term memory. In the PI paradigm, subjects are presented with a list of three (sometimes more) items that are designated the to-beremembered (TBR) items. After a distraction period subjects are prompted to recall these items. The original research varied the amount of time the distraction interval lasted (Brown, 1958; Peterson & Peterson, 1959). They found that the longer retention interval resulted in a greater memory decrement. Brown (1958) postulated that memory loss after repeated trials was a result of decay. The decay theory states that information presented to the memory system starts to deteriorate immediately and automatically from short-term memory. He found a decrement in memory performance, as a function of time (Brown's finding was used to validate the decay theory). He presumed that because memory performance decreased as the retention interval increased, it must be the increased length of time that is responsible for poor memory performance. However, Keppel and Underwood (1962) found that by maintaining a constant retention interval, there was still a decrement of memory from the first to the later trials when utilizing the same type of distractor task as Peterson and Peterson (Wickens, 1970). This finding led Keppel and Underwood to suggest that there was another process other than decay contributing to the loss of memory. They introduced a theory of memory loss being "attributable to PI [Proactive Interference] from previous items" (Baddeley, 1966, p. 302). Wickens (1970) was interested in determining what mechanism might compensate for the effect of PL He began an intensive study of the release from PI phenomenon. In Wickens' research, four trials were conducted in one category (e.g., fish). The study items were then changed to another category (e.g., tools) on the critical trial. He found that on this MODERN PSYCHOLOGICAL STUDIES 57 William J. Thornton and Bennett L. Schwartz on the critical trial. He found that on this crucial trial, when the category was changed, the subjects showed improved memory for the new category items. Thus, after having been given four consecutive trials of four words in each trial, the subjects have learned a total of 16 items from the same category (e.g., fish). If asked to recall the last group of four fish names, the subjects will have the previous 12 names of fish interfering with his or her memory. However, on the fourth trial, if the category was shifted to tools the subjects would have only four tools to remember, with no prior tools impeding upon the memory of those four. Thus, release from PI allows memory performance to improve. Gardiner, Craik, and Birtwhistle (1972) referred to the 1970 study by Wickens in which summarized several prior studies which demonstrated that "rapid accumulation of PI depended upon similarity, across trials, of the TBR [tobe-remembered] items and further that performance could be restored almost to the original level if, on the next trial the TBR items were drawn from a different class" (p. 778). However, despite the general agreement as to the value of the release from PI effect when studying encoding, there is still no clear determination of the underlying causes. Gardiner et al. (1972) summarized three basic hypotheses that could account for the release from PI. The first explanation is Wickens' (1970) attentional hypothesis which states that the subjects are alerted by the change in the TBR material on the critical trial and consequently gives more attention to the new materiaL The second possibility described by Gardiner et al., is Posner's storage hypothesis which suggests that "PI reflects spontaneous interaction during storage between the traces of current items and those of similar items stored from preceding trials. By this view the 'release' items are less vulnerable to intertrial interference" (p. 778-779). The third interpretation offered by Gardiner et al. was the retrieval hypothesis, attributed to Wickens. In this hypothesis, once "the TBR material is changed, the novel items supply a new, and thus more effective retrieval cue" (p. 779). Wicken's research demonstrates that switching to a new category allows memory performance to increase to first trial levels. However, it is not clear from his work as to what defines a category. In fact, Gardiner et al. (1972) found no release when subjects were not informed about a subtle category shift (e.g. garden flowers to wild flowers). It may not be that categories, per se, are responsible for the release phenomenon. Rather, subject's subjective expectations may play a key role in the release phenomenon. As such, we suspected that subjective expectations alone may lead to the release from PI. To test this, we lead people to believe a category-shift had occurred when, in fact, no shift actually occurred (O'Neill, Sutcliffe & Tulving, 1976). Our hypothesis was in partial agreement with each of the three hypotheses summarized by Gardiner et al. (1972). As with the attentional hypothesis, we too suspected that the subjects would be alerted by the change in category. This would allow the subjects to give more attention to the new material because the prior material is not going to be requested at recall. However, we suspected that the same effect would occur if the subjects thought that the category had changed even when the category remained constant. As to the storage hypothesis, we anticipated that the release items were less vulnerable to intertrial interference. However, it was our suggestion that this was a result of the subject's subjective expectation that information from the prior category would not be required at test, rather than the fact that it would not. As to Wickens' retrieval hypothesis, we proposed that it was the belief of category change that supplied the new, and thus more effective retrieval cue, rather than the change itself. We suspected that the mechanism responsible for the release from PI was not the actual change in categories, but rather it was the subjective expectation that allows people to reorganize memory output, and thus permits release whether or not the category had actually changed. 58 MODERN PSYCHOLOGICAL STUDIES