Encoding and interference effects on visual working memory binding in young and older adults

This Economic and Social Research Council-funded project was aimed at investigating the existence of age-related binding deficits in visual working memory, and to establish the possible role of encoding processes. There were three specific objectives:

1) To determine whether or not encoding time influences binding efficacy in older adults. Experiment 1 was designed to test the hypothesis that older adults' binding memory performance may suffer only when exposed to longer-than-required encoding durations, potentially implicating a central executive deficit.

2) To investigate the effects of presentation format (i.e., simultaneous – all at once – or sequential – one item at a time) and, within the sequential condition, whether serial position effects exist in binding memory performance. Experiment 2 was designed to reveal any difficulties experienced by older adults during the encoding phase of the task, which would have indicated limited central executive and/or working memory storage capacity.

3) To test the theory that older adults are less able than young adults to inhibit irrelevant information from working memory. Experiment 3 was designed to involve the brief presentation of a suffix (a new object irrelevant to the task) immediately after encoding of the to-be-remembered items. If older adults were more affected than young adults, reduced inhibitory processes would be implicated.

The purpose of this ESRC research grant was to increase our understanding of the cognitive mechanisms involved in the ability to associate visual features, specifically colours and shapes, in short-term ('working') memory in younger and older adults. Previous research has suggested that storing associated information in long-term memory, such as names and faces, is specifically affected by the healthy ageing process, but much less is known about the ability to create and maintain temporary associations ('bindings') in the working memory domain. Although previous research has established that binding in visual working memory is reliably affected by pathological ageing processes such as Alzheimer's disease, there is debate surrounding the existence of such a binding deficit with reference to healthy ageing. The present grant was aimed at determining the extent to which an age-related binding deficit exists in visual working memory and specifically focused upon understanding whether or not limitations in encoding (i.e., when initially perceiving the information) could be involved in any deficit.

As a result of this project, our empirical and theoretical understanding of binding in visual working memory has advanced. Generally, there has been relatively little research focusing specifically on temporary binding of visual material, and much less research that has investigated performance in older as well as younger adults. The research has therefore contributed necessary empirical data to this area of study. Theoretically, as a result of the grant, we now have a greater understanding of temporary visual feature binding and the effects of ageing on the processes involved in this ability. We now know that, when considering the binding of surface visual features (colour and shape), supporting previous conclusions in the literature, healthy older adults are generally able to create and maintain temporary surface visual feature bindings. Although deficits have occasionally been observed, they have been small and unreliable, relative to those reported in the literature on long-term memory and on pathological ageing. Finally, the research demonstrated theoretically interesting limitations regarding how older adults encode information in visual working memory, which may indicate deficits in attentional and/or storage capacity.