The effects of ageing, task interruption and planning on prospective memory

Abstract

Prospective memory involves an individual remembering to perform an intended action at some designated point in the future such as taking medication at a certain time. This type of memory has been demonstrated to decline with advancing age in previous computer-based, laboratory studies. However it appears intact when investigated via naturalistic, community-based designs. Because few studies have investigated everyday prospective memory tasks in a reliable and experimentally rigorous fashion this dissertation will attempt to do so via two studies. The main aim of Study 1 was to develop and test a new naturalistic paradigm set in a ‘homelike’laboratory and to empirically investigate the effects of three variables of interest on prospective memory performance (viz., ageing, interruption and planning). The performance of 79 younger (age range = 18-33 years, M = 21.44 years, SD = 4.53 years) and 67 older adults (age range = 60-75 years, M = 68.23 years, SD = 4.13 years) was compared on three prospective memory tasks (e.g. event-, time- and activity-based tasks). Participants were engaged in planning a meal (ongoing task) by searching through cupboards for ingredients, looking in a recipe book and checking prices in a price catalogue. Simultaneously, participants were required to place a white sticker on recipes with a dairy product (event-based task), press pause on the VCR every 5 minutes (time-based task) and ask for their watch or mobile phone at the completion of the ongoing task (activity-based task). Results of separate ANOVA’s suggested that younger adults outperformed older adults on the event- and time-based tasks, whilst no age-related differences were apparent on the activity-based task. Findings support the notion that cognitively demanding tasks disadvantage older adults due to reduced cognitive resources. In addition, Study 1 attempted to investigate two relatively neglected variables within the prospective memory field, namely; interruption and planning. Considering that the performance of prospective memory tasks is imperative for independent living, variables that disrupt (e.g., interruption) and facilitate (e.g., planning) this process need to be understood. A group of participants (younger and older adults) were interrupted twice by the unexpected ringing of a mobile phone and the experimenter entering and searching the laboratory. The event- (dairy product) and time-based (VCR) tasks were disrupted significantly by the interruption. Performance on all three prospective memory tasks was improved when participants had the opportunity to spend 5 minutes taking notes and planning how they would perform the tasks. Planning was able to overcome the negative (albeit non significant) effects of an interruption on the activity-based (item) task and age-related differences on the time-based (VCR) task. These findings suggest that interruptions are complex in nature and may have a greater effect on tasks that have cues of low saliency (e.g., time on a clock) that require self-initiated retrieval processes. In addition, self-reports of how participants recalled the tasks and why they forgot them suggested that one strategy was not effective for all three prospective memory tasks. These findings may be used to inform educational and training programs. The main aim of study 2 was to determine whether 6 neuropsychological measures (viz., 4 disc Tower of London (TOL-4), the Stroop Color-Word Interference Test (Stroop), Controlled Oral Word Association Test (COWAT), Trail Making Test-Part B (TMT-B), Wisconsin Card Sorting Test (WCST) and Letter/Number Sequencing Test (LNST)) of prefrontal functioning (e.g., planning, inhibition, cognitive fluency and flexibility, set shifting and working memory respectively) could predict prospective memory performance. A logistic regression indicated that the prefrontal measures were able to predict performance on the event-based (dairy product) task for younger adults only. More specifically, scores on the TMT-B and LNS were significant predictors of event-based task performance for younger adults. Older adults’ performance on the time-based (VCR) task was predicted by scores on the TMT-B. In addition, the performance of younger adults on the activity-based (item) task was predicted by scores on the COWAT. It was concluded that prefrontal processes are involved in prospective memory performance and that the characteristics of the prospective memory tasks influence which processes are involved. Support for the frontal lobe hypothesis of ageing was provided as age-related differences were found on the prefrontal measures, with the exception of the COWAT. Future research is recommended to compare the performance of participants on the three everyday prospective memory tasks and computerised tasks to determine whether the two paradigms are measuring the same construct.