Ageing and Uncertainty: An Exploration of Age Related Patterns of Information Processing in Working Memory in Response to Uncertainty

Stephens, Stephanie (2007). Ageing and Uncertainty: An Exploration of Age Related Patterns of Information Processing in Working Memory in Response to Uncertainty PhD Thesis, School of Psychology , University of Queensland.

       
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Author Stephens, Stephanie
Thesis Title Ageing and Uncertainty: An Exploration of Age Related Patterns of Information Processing in Working Memory in Response to Uncertainty
School, Centre or Institute School of Psychology
Institution University of Queensland
Publication date 2007
Thesis type PhD Thesis
Supervisor Associate Professor Kenneth McFarland
Abstract/Summary The present study was developed within the information theory, working memory, and cognitive ageing paradigms. The overall aim of the present study was to investigate the age related differences in the patterns of processing uncertainty within the theoretical construct of working memory, particularly the central executive, the episodic buffer, and the visuospatial sketchpad. The uncertainty associated with responding to stimuli is a complex construct that has received little attention in either the ageing literature or the working memory literature. The present study developed choice reaction time tasks based on the findings of Hick (1952) and Hyman (1953), in which the participant’s choice reaction time to a stimulus was shown to depend on three main variables. These three variables were found to vary the uncertainty associated with responding to a stimulus. The first variable was the stimulus set size. The number of stimuli was operationalised by the number of locations, four or eight, from which stimuli could appear. The second variable was condition probability. The currently appearing stimulus could appear from any one of four or eight locations. The current stimulus appeared with a probability equal to the other stimuli appearing in the condition, or appeared with a probability that could be different to the probabilities of other stimuli appearing in the condition. Thus, the current stimulus could appear within an equiprobable or a nonequiprobable condition. The third variable was the probability of appearance of the current stimulus. In the present study the current stimulus probability was manipulated to be either 0.250 or 0.125. These variables were manipulated in order to investigate the effect of responding to uncertainty across the healthy adult lifespan. In general, increasing age increased choice reaction time in response to the current stimulus under all experimental conditions, and increasing choice number significantly increased choice reaction time for all age groups. The literature review in chapter 1 highlighted the difficulties in assessing age related response differences in tasks that measure executive processes. In this chapter it is suggested that the methodology used in choice reaction tasks, developed within the information processing and “uncertainty” paradigm, may provide an insight into how and what changes occur to executive processing over the healthy adult lifespan. The results in the present study were interpreted within the theoretical structure of Baddeley’s (2000b) model of working memory. This gave an explanatory framework to the age related patterns of choice reaction time responses. The experiment in chapter 2 examined the second variable, condition probability. The differences in choice reaction time responses between an 8 choice equiprobable condition and an 8 choice nonequiprobable condition, and between a young and an old age group, were explored. There was a significantly faster choice reaction time in response to the 8 choice nonequiprobable condition for both age groups. However, there was a disproportionately faster choice reaction time response to the 8 choice nonequiprobable condition by the older age group. The results suggested that the uncertainty associated with responding to stimuli was not only dependent on the equiprobable or a nonequiprobable condition in which the current stimulus appears, but also vulnerable to the effects of age. The results suggested that an episodic buffer (Baddeley, 2000b) supplies a central executive with precise information concerning condition probability. The choice reaction time responses indicated that a calculated amount of information using the probabilities of appearance of the stimuli does not explain the total uncertainty associated with the stimulus. The experiments reported in chapter 3 used single response tasks and chapter 4 used dual response tasks. These experiments examined condition probability again, along with the first variable, effect of choice set size, and the third variable, the current stimulus probability. Healthy adult participants aged from late teens to eighties were included. The choice reaction time responses in nonequiprobable conditions, compared to equiprobable conditions, were faster in response to both stimuli probabilities. Responses to the stimulus probability of 0.125 in the nonequiprobable conditions in both single and dual tasks were always significantly faster compared to the stimulus probability of 0.250 for all age groups. The older age groups’ choice reaction times were disproportionately slower in response to the stimuli of probability 0.250, compared to 0.125. This suggested that the central executive retains priority in responding to stimuli with a low probability, 0.125, in older age groups. The disproportionate response by the older age groups to stimulus probability, compared to the younger age groups, also suggested that the episodic buffer may not be as affected by increasing age as other working memory components. This also suggested the information held in the episodic buffer affects the speed of processing. The choice reaction time response patterns to both stimulus probability and condition probability were the same in the dual task conditions, compared to the single task conditions, for all age groups. The experiment in chapter 5 addressed the issue that the choice reaction time results were based on a small number of stimulus presentations per trial, and the response patterns may not be able to be maintained over a longer trial period. Thus, the temporal stability of the response to uncertainty was examined. Results were consistent with the proposal that there is temporal stability in processing uncertainty by all age groups in an extended task, and that the results did not arise because the choice reaction time patterns were a results of shorter trials requiring less sustained effort. Chapter 6 summarised the results found in the present study and interprets those results in terms of Baddeley’s (2000b) theoretical model of working memory, age related response decrements, and uncertainty. The main conclusions were that first, the fastest choice reaction time, for all age groups, is in proportion to the greater uncertainty associated with the stimulus, and in proportion to the greater uncertainty of the context in which the stimulus appears. Second, the gradual age related slowing of choice reaction time responses to the current stimulus indicated a gradual increase in the speed of decision processing within the central executive. Third, the results indicated the information temporarily held in the episodic buffer affects the speed of processing. Fourth, the results indicated that the episodic buffer ages less than the central executive. The uncertainty associated with responding to stimuli with differing probabilities of appearance was found to be an excellent instrument in examining aged changes in working memory.

 
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