Critical evaluation of interference-based accounts of forgetting via studies of minimal interference
Embargo end date26/06/2021
McGhee, Jamie D.
There is a growing consensus that the forgetting of information from long-term memory occurs as a result of interference. Interference is experienced when the encountering of extraneous stimuli impedes the retention and later recall of a desired memory. Interfering stimuli may be encountered before (i.e., proactive interference) or after (i.e., retroactive interference) the encoding of a given memory. The minimisation of interference via wakeful rest has been seen to improve retention of newly acquired episodic memory (Dewar, Pesallaccia, Cowan, Provinciali, & Della Sala, 2012; Alber, Della Sala, & Dewar, 2014; Ecker, Tay, & Brown, 2015a; Ecker, Brown, & Lewandowsky, 2015b). However, conceptions of how interference elicits forgetting – and how its minimisation may promote successful retention - vary across different theoretical accounts. According to consolidation theory (Müller & Pilzecker, 1900; Wixted, 2004; Dudai, 2004), forgetting is elicited by the disruption of early consolidative processes following postencoding engagement in further sensory stimulation. It is believed that the interruption of this process is avoided when encoding is immediately followed by a period of wakeful rest, in which disruptive sensory stimulation is vastly reduced. Alternatively, the temporal distinctiveness theory (Brown, Neath, & Chater, 2007) posits that forgetting is incurred following the reduced distinctiveness of a specific memory at retrieval, which is partly mediated by the proximity of neighbouring memories encountered either before or after target acquisition. Under this account, if a target memory is temporally isolated by either pre- or post-encoding intervals of rest then the increased distinctiveness of this memory will improve retrieval. Over the course of this thesis, I aim to explore the possible benefits of minimal proactive and retroactive interference across seven experiments as a means of critically evaluating the accountability of these theories in explaining forgetting across a spectrum of memory ability. In Chapter 1, I review the literature exploring the effects of interference and benefits resulting from wakeful rest seen across both healthy populations and patients with anterograde amnesia. I also outline the mechanisms proposed by both the consolidation theory and the temporal distinctiveness theory and highlight key deviations. In Chapter 2, I explore two experiments (Experiment 1 and 2) which aimed to assess whether healthy younger and older adults retained more prose material when encoding was preceded and/or followed by wakeful rest. We found that both healthy younger and older adults groups were able to retain substantial amounts of prose information irrespective of whether they rested wakefully or engaged in an effortful task before or after prose encoding. I conclude that healthy adults may benefit from the use of retrieval strategies that are applicable only in the retention of prose material specifically. I propose that the maintenance of interference-resilient cues derived from salient story ideas allowed for the circumvention of interference effects following pre- and post-encoding activity. In Chapter 3, I explore this idea further via two experiments which assessed whether healthy older adults would continue to demonstrate a lack of interference effects if the to-be-retained material did not readily allow for the use of facilitatory retrieval strategies. The same paradigm used in Experiment 1 and 2 was adopted, with the exception of different to-be-retained material (i.e., lists of unrelated words) and the use of a more intensive version of the Spot-the-Difference task. In Experiment 3, healthy older adults were seen to forget significantly more wordlist items following both pre- and postencoding engagement in a more demanding Spot-theDifference task. While an observed individual pre-encoding wakeful rest benefit provided support for the temporal distinctiveness theory in Experiment 3, Experiment 4 demonstrated that this evidence was likely the result of crosslist interference, with results indicating no interference effects within a between-subjects design. In Chapter 4, I reflect on another experiment which adopts the same paradigm used in Experiment 1 and 2 in order to assess whether patients presenting with anterograde amnesia would show improved retention of prose material following pre- and/or post-encoding wakeful rest (Experiment 5). In Experiment 5, amnesic patients retained significantly more prose material across conditions in which wakeful rest followed encoding. However, a superadditive decline was observed following both pre- and post-encoding engagement in a spot-the-difference task within a single condition. Given the absence of an individual pre-encoding wakeful rest benefit in this experiment, it was concluded that the results provided evidence in support of the consolidation theory as the more accountable theory of forgetting. In Chapter 5, I cover Experiment 6 which aimed to see whether the consistent benefits of post-encoding wakeful rest to the retention of episodic information from long-term memory could also be observed in tests of prospective memory (PM). In this experiment, both healthy younger and older adults were able to successfully identify cues and recall associated items irrespective of whether wakeful rest followed PM test instruction. However, I highlight that assessing the benefits of post-study wakeful rest in a typical study of PM is significantly limited by the employment of multiple learning trials. Given that participants are repeatedly exposed and tested on the target material during the initial learning phase of the experiment, I conclude that the target material has likely been adequately stabilised in long-term memory prior to the occurrence of postencoding activity. In Chapter 6, I discuss the final experiment that intended to see whether the administration of benzodiazepines (BZs) across a sample of healthy adults would result in observed memory performances that mirror specific profiles of anterograde amnesia. Additionally, the study intended to establish whether forgetting following drug-induced amnesia would be alleviated by post-encoding wakeful rest. While BZs ingestion did result in poorer recall of prose material learned after drug administration, forgetting was not reduced following post-encoding wakeful rest as typically seen in many amnesic patients. Given this, I conclude that the administration of BZs results in a temporary state of severe anterograde amnesia, in which an ability to benefit from the minimisation of sensory stimulation following is briefly unavailable. In Chapter 7, I provide a general discussion of the findings from all seven experiments. In this discussion, I assert that the consolidation theory provides a more viable explanation of forgetting among individuals with anterograde amnesia. However, I acknowledge practical constraints of investigating interference effects and the observed limits of wakeful rest benefits. Mainly, how wakeful rest benefits are difficult to assess across healthy populations under certain conditions (i.e., learned materials facilitate retrieval strategies, Experiment 1 and 2; interpolated tasks do not elicit interference alone, Experiment 3 and 4; learned materials can be stabilized prior to further sensory stimulation, Experiment 6).