Information Processing Speed in Ageing: Is it task dependent?

Evidence indicates that information processing speed slows as age increases and disproportionately so with impaired cognition and various neurodegenerative diseases such as Alzheimer’s disease. The new DSM-5 criteria for neuro-cognitive disorders state that measuring information processing speed associated with attentional function should be included within dementia diagnosis. However, what is not clarified is that outcome variability can occur, in part, as a result of methodological factors i.e. type of attention-related test/ attentional function and by person-related factors such as sex and education. In addition, there appears to be a dichotomy between the types of tests used within research studies and clinical settings which should be addressed [Haworth et al, 2016].The aim of the research presented in this thesis was to investigate how using different tests of attentional function in similar groups of young and older adults may affect the outcome measure of information processing speed (RT) and its variability (IIV). Part of this aim was to determine whether the number of trials may influence performance i.e. RT, IIV and accuracy (number of errors). Another aim was to determine whether result outcome is affected similarly across tests by a variety of person-related factors i.e. sex, education, objective cognitive measures and particularly previously un-tested factors of subjective memory function and perceived test difficulty which may help determine whether subjective feelings are associated with slower and more variable information processing speed and may influence study outcome.The first study [Chapter 2] comprised of a visual search test commonly used in research as a sensitive measure of ageing upon RT and IIV and attentional shifting, yet not examined particularly in relation to subjective memory function and perceived test difficulty. Results indicated that information processing speed was significantly slowed in older compared to younger adults and attentional shifting was poorer in older adults. There was no relationship with subjective memory function whereas the influence of sex, education and perceived test difficulty were dependent on the condition and age.In the second, larger study including the Trail Making Test (TMT), Simple reaction time (RT) test, Choice RT test and Multi-Item Localization test (MILO) [Chapters 3- 5], the results indicated that in all tests older adults were significantly slower and more variable than young adults at group level. Person-related factors were influential depending on the test used. Subjective memory function and education were only influential within conditions of the MILO and perceived test difficulty influential in Trails B and Choice RT. Large effect sizes in visual search, MILO and the Choice RT suggested they were most sensitive to ageing effects. In conclusion, we speculate which attentional tests may be more useful in research and than those already used in clinical settings i.e. TMT and highlight the need to take into consideration different factors depending on the attentional test used so as not to misinterpret normal levels of information processing speed in ostensibly healthy aging