Effects of attention on the precision of neural and mnemonic representations in healthy ageing
Episodic memory is an integral cognitive function, and its decline is a hallmark symptom of cognitive ageing. Amongst the various memory processes, it is well established that ageing particularly impacts recollection. Emerging studies using sensitive behavioural and imaging techniques indicate that ageing compromises the precision or fidelity of memory representations. The degradation of both mnemonic and neural fidelity is thought to contribute to age-related changes to episodic memory. Further, episodic memory does not operate in isolation, rather selective attention influences the encoding and retrieval of information that are relevant to current task-goals. This thesis explores the impact of age-related attentional dysregulation on associative binding and the fidelity of associative memories at encoding. I also explore the effects of selective attention and non-invasive stimulation on age-related retrieval precision using continuous-report tasks. Chapter 2 examines the hyper-binding effect, an age-specific phenomenon exhibited as older adults forming excessive associations between task-relevant and -irrelevant information. This effect has reportedly been found when distractors involved task-irrelevant words. The results from this experiment showed that the hyper-binding effect extends to perceptually rich (famous faces and scenes) distractors. Using a two-alternative forced-choice test, older adults were negatively impacted by previous exposure of distractors as evinced by lower recognition for rearranged pairs relative to intact pairs. However, using a cued-recall test, an age-invariant memory advantage was found for intact pairs relative to rearranged pairs. Extending from Chapter 2, Chapter 3 investigated the neural correlates of distractibility and whether poor attentional control modulates the neural fidelity of associative memory at encoding. The findings revealed that older adults were susceptible to interference, indicated by reduced activation in inhibitory control regions coupled with increased distractor-related activation in category-selective regions. Further, the hyper-binding effect impacted the regional BOLD activation, but not the fidelity of representations in category-selective regions. Chapter 4 utilised a continuous-report task to examine whether spatial pre-cues can modulate retrieval precision for comparable representations in WM and LTM. Spatial pre-cues were found to modulate WM retrieval precision, though the observed attentional effects on precision lessened for LTM representations. Chapter 5 also employed a continuous-report task to examine whether non-invasive stimulation to the angular gyrus enhances the quality of episodic representations. Results demonstrate that angular gyrus stimulation only enhanced retrieval error performance in younger adults but did not yield facilitatory effects on model-driven retrieval precision or success measures across age. Collectively, the experiments in this thesis demonstrate that poor attentional control impacts episodic memory performance in ageing. The findings in this thesis support previous work by highlighting the interplay between attentional processing and episodic memory. Further, non-invasive stimulation may not be an effective strategy for ameliorating precision deficits in ageing.
Ageing, Cognitive decline, Memory, Attention, Inhibitory deficit
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