published_or_final_version / Clinical Psychology / Doctoral / Doctor of Psychology

published_or_final_version / Human Performance / Doctoral / Doctor of Philosophy

This thesis contains two studies which examined the cognitive functioning of the aging brain. Specifically, age-related changes in processing speed and its remediation via cognitive training were studied. In study 1, younger adults (n = 34) and older adults (n = 39) were recruited to investigate the age-related differences in the relationships between processing speed and general cognitive status (GCS). Their performance in GCS (as measured by The Montreal Cognitive Assessment, Hong Kong Version), cognitive processing speed (as measured by Processing Speed Index, Wechsler Adult Intelligence Scale), cognitive inhibition (as measured by Stroop Color-Word Test), and divided attention (as measured by Color Trails Test) was examined. Current findings indicated that processing speed predicted GCS in older but not younger adults. In older adults, processing speed as a predictor accounted for an additional 13% of variance in GCS. This study further verified the relationship between processing speed and prefrontal abilities, including verbal fluency, cognitive inhibition and divided attention in aging. Findings revealed that despite the abovementioned prefrontal abilities were significantly correlated with processing speed, verbal fluency had remained the strongest predictor, accounting for 21% of variance in processing speed in older adults. Based on findings in study 1, it was anticipated that training cognitive skills including processing speed and prefrontal abilities in older adults would improve cognitive functioning in general. Therefore, in study 2, elderly people at risk of progressive cognitive decline (n = 70) were recruited to investigate the training effect of computerized cognitive training programs that aimed to improve cognitive processing speed, cognitive inhibition and divided attention. Findings indicated that cognitive processing speed and divided attention improved post-training. Results obtained from the two studies implied potential intervention through training cognitive processing speed in elderly people at risk of progressive cognitive decline. Future studies should focus on training specific effect and examining the optimal effect by modification of the training paradigms, particularly the design of the contents and level of difficulty. / published_or_final_version / Clinical Psychology / Doctoral / Doctor of Psychology

This thesis is concerned with current debate about alternative 'lexical' and 'episodic' accounts of repetition priming in visual word perception. Like some previous research, the present study investigated effects of 'context congruence' of pre-test and test word presentations. However, modified methods were employed to limit methodoligical problems observed in previous research and to treat the issue of strategic control in repetition priming. The experiments investigated the effect of test orienting tasks which either did or did not require subjects to engage in deliberate remembering of pre-test context. A recognition-memory orienting task was employed to induce deliberate remembering and a letter-judgement orienting task was employed to avert deliberate remembering. Experiment 1 demonstrated a strong effect of orienting tasks in a naming task; repetition priming was reliably greater in the recognition-memory condition. The effect was replicated in a 'restricted' tachistoscopic identification task in Experiment 2, suggesting that the locus of the effect was within processes integral to word identification. Experiment 3 showed that the effect could not be attributed to an inadvertent masking of repetition priming in the letter-judgement conditions, or to be manipulation of subjects' prior knowledge of repetitions. Although these results provide new evidence of episodic memory coding in repetition priming, it can be argued that they do not necessarily imply that all repetition effects depend upon episodic memory coding. The remembering-enhanced repetition effect might reflect the superimposition of an exceptional autobiographical-memory repetition effect upon a normal lexical repetition effect. To test this possibility, Experiments 4 through 7 tested for evidence of dual memory components as a functional dissociation between normal and remembering-enhanced repetition effects. No evidence of a dissociation was found for the following expprimental manipulations: (1) modality of pre-test word presentation, (2) word frequency, (3) subjects' confidence criteria for word naming, (4) 'level of processing' of pre-test words. The discussion considers theoretical and methodological implications, and reviews some related research. The main conclusion suggests that the findings of this thesis are consistent with the assumption of a unitary episodic memory system underlying repetition priming and other phenomena of learning and memory, and that the findings pose some problems for alternative accounts.

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