An Investigation of Inhibitory Control and Attention Processes in Alzheimer’s Disease : An Eye Tracking study of Cognitive Impairment, Age and Ethnicity

Polden, Megan and Crawford, Trevor (2022) An Investigation of Inhibitory Control and Attention Processes in Alzheimer’s Disease : An Eye Tracking study of Cognitive Impairment, Age and Ethnicity. PhD thesis, Lancaster University.

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Abstract

Eye movements are involved in almost all aspects of daily life and can provide valuable insights into an individual’s cognitive functioning. The ability to inhibit irrelevant stimuli, engage and disengage attention and successfully execute saccades, are vital processes for most everyday activities. Neurodegenerative diseases such as Alzheimer’s results in a decline in executive functioning, working memory and inhibitory control capabilities. Areas of the brain and neuronal pathways that are involved in executing saccades, fixations and gaze patterns are often impaired in Alzheimer’s disease (AD) resulting in the deterioration of eye movements, attentional control and inhibitory control. Due to this, dysfunctions and abnormal eye movements can be a useful biological marker of cognitive impairment and decline. The current diagnosis procedure for AD and other forms of cognitive impairment are time consuming, invasive, costly and often lack the sensitivity to provide an early and timely diagnosis. Eye-tracking tasks assessing pro and antisaccades could aid diagnosis and monitoring of AD and provide early indicators of cognitive decline. Further, for a potential diagnosis tool to be successful, it must be robust and generalisable across multiple ethnic and age cohorts. Therefore, in this thesis, chapters 3-5 investigate saccade performance in participants with AD and mild cognitive impairment (MCI). To investigate the robustness and generalisability of novel and established eye-tracking paradigms, chapter 3 and 4 includes younger and older adult populations and both European and South Asian adults allowing the effects to be assessed in relation to ageing, ethnicity and disease effects. I first found that disengagement of attention capabilities were preserved in AD and MCI populations and that the gap paradigm was robust across various clinical groups, age cohorts and ethnic groups. Further studies investigated a novel eye-tracking paradigm designed to assess inhibitory control towards a specific distracter. Here, it was found that the inhibition of a recent distracter (IRD) effect, categorised by faster saccade reaction times towards a target presented in the location of a previous target compared to the location of a distracter target, was present in AD and MCI populations. This indicates that not all aspects of inhibitory control are impaired in AD populations as previously assumed. Attentional fluctuations when performing pro and antisaccades were investigated using a measure of coefficient of variation (CV) assessing saccade latencies. Results indicated that antisaccade mean latencies can distinguish clinical groups from controls however CV measures may not be sufficiently robust to provide reliable markers for cognitive impairment. In chapter 6 I shifted my focus and investigated the potential of bilateral eye movements to enhance memory and recall processes in healthy adults and clinical groups. It was found that the so-called saccade induced retrieval effect was unable to be replicated in younger and older healthy adults or clinical populations with cognitive impairment bringing into question the robustness of this effect. The work reported in this thesis develops our understanding of oculomotor processes across multiple age cohorts, ethnic groups and clinical populations. In particular, I argue that future research should strive to involve more diverse population samples and provide a greater focus on investigating preserved effects and capabilities in clinical populations.