Forgetting in Alzheimer's disease: Is it fast? Is it affected by repeated retrieval?

Abstract

Objectives: Whether people with Alzheimer's Disease present with accelerated long term forgetting compared to healthy controls is still debated. Typically, accelerated long term forgetting implies testing the same participants repeatedly over several delays. This testing method raises the issue of confounding repetition effects with forgetting rates. We used a novel procedure to disentangle the two effects. Methods: Four short stories were presented during an initial in-person assessment of 40 patients with Alzheimer's Disease and 42 age-matched healthy controls. Our aim was for participants to reach a score of 70% correct (9 out of 13 questions) at encoding. If this criterion was not achieved after the first trial, the four stories were presented again (in a different order); participants took the 1 min filler task again and were then retested. We repeated this process until participants reached the 70% criterion or to a maximum of four trials. Cued recall memory tests were completed during follow-up telephone call(s) at different delay intervals. Study material was presented only at encoding, then probed with different question sets on all other delays. Each question set tested different sub-parts of the material. The experiment employed a mixed design. Participants were randomly allocated to either a condition without retrieval practice or a condition with retrieval practice. Participants in the condition without retrieval practice were only tested at two delays: post encoding filled delay and at one month. Participants in the condition with retrieval practice were tested at four delays: post encoding filled delay, one day, one week and one month. Our methodological design allowed us to separate the effects of retesting from the effects of delay. Results: Alzheimer's Disease patients showed a significant encoding deficit reflected in the higher number of trials required to reach criterion. Using Linear Mixed Models, we found no group by delay interactions between the post encoding filled delay retrieval and one month delays, with Alzheimer's Disease groups having a similar decline in performance to healthy controls, irrespective of testing condition. Significant condition by delay interactions were found for both groups (Alzheimer's Disease and healthy controls), with better performance at one month in the condition with retrieval practice. Conclusions: Our data showed that Alzheimer's Disease is not characterised by accelerated long term forgetting, patients in our sample forgot at the same rate as healthy controls. Given the additional trials required by Alzheimer's patients to reach the 70% correct criterion, their memory impairment appears to be one of encoding. Moreover, Alzheimer's Disease patients benefited from repeated testing to the same extent as healthy controls. Due to our methodological design, we were also able to show that performance improved under repeated testing conditions, even with partial testing (sampling different features from each narrative on every test session/delay) in both health...

Diminished Learning Over Repeated Exposures (LORE) in preclinical Alzheimer's disease

“…The differential relationship between same versus alternate face‐name memory and AD biomarkers highlights that a core AD cognitive profile is characterized by failures in learning despite repeated exposure to the same stimuli over discrete testing sessions. Practically, these results suggest that the critical element of “diminished practice effect” as a measure of prognosis or risk likely rests in failure of memory for repeated items 9 . Furthermore, practice effect paradigms that do not incorporate repeated items will likely be insensitive to prognosis/risk.…”

“…However, the specific cognitive mechanisms underlying the practice effect have not been well‐specified. Two types of practice effects exist, with the latter being, in our view, most relevant to AD: (1) general practice effects associated with task familiarity (eg, development of test‐taking strategies, reduced test anxiety) and (2) memory for the specific test items previously encountered, which we term “learning over repeated exposures” or LORE to distinguish from general practice effects 9 …”

Lower practice effects as a marker of cognitive performance and dementia risk: A literature review

“…It should also be considered that, as our primary focus was on PEs as a potential marker for cognitive decline, we included only articles that were assigned to Category C. Therefore, we excluded several articles that focused on understanding mechanisms underlying PEs, for example, by determining whether PEs can be attributed to repeated content rather than context effects, 50 or by investigating different aspects of memory (eg, encoding vs. retrieval) as underlying mechanisms of PEs 51 . We note that those and other articles were not overlooked in the review process, but rather fell outside the scope of the current review.…”

Rate of forgetting is independent of initial degree of learning

“…Third, the social distancing measures adopted during the COVID-19 pandemic rendered testing in person impossible. Testing via telephone has been shown to be an appropriate method of assessing long-term forgetting (Allen et al, 2019) and has been used in studies with similar paradigms to the one in the present study (e.g., Stamate et al, 2020).…”

“…Considerable evidence has been accrued showing that repeated retrieval of encoded material enhances learning (review in Roediger III & Butler, 2011). To minimise these practice effects at each testing phase, only a subset of the sentences was tested at any given delay (Baddeley et al, 2019;Stamate et al, 2020). Hence, each response sheet contained one of three subsets of 12 sentences taken from the 36 sentences presented in the study trials.…”