User:EmmaMcCormack/sandbox

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Cognitive slowing has been theorized to be an underlying pinning of age related decline in a variety of cognitive abilities ^[1]. Such slowing includes slower processing speed, reduced attentional abilities and reduced working memory abilities ^[2]. A single reason to why slowing occurs has not been determined. It is believed to be a result of either reduced neural connections^[3], greater noise in the nervous system ^[4] or an increased proportion in the loss of information at each step of processing ^[5]. Nonetheless research has identified that older adults response latencies, when measured across a range of cognitive tests, are approximately 1.5 times slower than younger adults ^{[3] [5]}

Research has indicated that the speed of reading declines with age. This is due to older adults spending more time reading complex sentences in order to recall the information correctly. In comparison younger adults take longer reading infrequent words and new concepts introduced into a particular text ^[6]. Research has also suggested that cognitive slowing is associated with language comprehension and recollection. For example, older adults portrayed greater difficulty recalling speech segments when they were presented at a fast rate ^[7] and when given the option older adults chose to listen to shorter slower speech segments ^[8]. Cognitive slowing has also been associated with reductions in fluid intelligence ^[9] and recognizing famous names and faces ^[10]. Although opponents argue the idea of cognitive slowing is a reductionist approach ^[11], a link has formed between cognitive speed and competent performance on everyday living tasks such as reading medication labels, counting out change and looking up numbers in a phone book ^[12].

The second theory of cognitive aging proposes that aging weakens inhibitory control, making it difficult for older adults to suppress irrelevant information ^[13]. A fast and accurate mental life requires an ability to (a) control access to attention’s focus (b) delete irrelevant information from attention and working memory and (c) suppress inappropriate responses ^[14]. Thus an inefficient inhibition framework makes it more difficult for aging adults to accurately process and carry out certain tasks.

Research has indicated that older adults are easily distracted while reading, for example, by a word printed in a different typeface. As a result the speed of reading is reduced and comprehension and memory of the text declines ^{[13] [15]}. The inability to suppress irrelevant information also affects the ability to ignore distracting speech while carrying out a task. Consider a study conducted by Tun and colleagues, which compared the ability of young and old adults to ignore competing speech while listening to word lists. Results supported the inhibition deficit theory as older adults were less able to suppress the competing speech and recalled fewer words ^[16]. A recent study supported such findings as individual differences in inhibitory control were found to predict interference from a competing talker ^[17]. Research has suggested that the inhibition deficit also contributes to problems when identifying words. In particular when low frequency words (e.g. brood and wool) ^[18] and lengthy words (e.g. holiday) ^[19] are used.

The third cognitive theory of aging, developed by Burke, MacKay and colleagues (1991), proposes cognitive decline occurs as a result of weakened memory connections which lead to poorer activation of target information ^[20][21][22]. This theory states language production relies on the strength of connections within a network that includes semantic (conceptual) and phonological (speech sounds) levels. According to Burke and MacKay, the phonological level is more susceptible to lapses in retrieval as there are no inherent connections between word sounds in comparison to inherent connections between concepts. Therefore when certain words are not used recently or frequently, the phonological connections weaken even further making it difficult to retrieve a word even when the meaning is known. This theory is often supported by the tip-of-the-tongue-experience (TOT) ^{[20] [23]}.

Frequencies of TOTs increase throughout adulthood as a result of age related weakening between the semantic and phonological links ^{[20] [23]}. When older participants were provided a definition of an infrequent word (e.g. umbrella), they were often able to evoke the meaning and/or visualize the object but not retrieve the actual word. Thus supporting the idea of semantic and phonological representations ^[23]. TOT’s are more frequent when a word is presented as a proper name (e.g. Mr Farmer) compared to an occupation (e.g. farmer) ^[24]. It is argued the semantic connections are stronger for common names (such as occupations) as there is often more than one acceptable name for the item (e.g. farmer, farmhand, rancher)^[25].Fortunately it is suggested connections between semantic and phonological levels improve with greater use ^{[23] [26]}.

The disciplines of cognitive psychology and neuroscience have recently come together to investigate the neural bases of cognitive aging ^[27]. This approach proposes that neurobiological changes are at the root of normal cognitive decline in old age. Deficits in domains such as working memory, attention and executive functions, are similar to neuropsychological profiles of individuals with brain damage to the prefrontal cortex ^[28][29].

Research has indicated that older adults do not activate areas in the frontal cortex to the same extent of younger adults. For example, less activation was found when participants purposefully committed information to memory ^[30] and when participants memorized faces ^[31]. This reduced activation may be due to age related change in brain size, in particular a reduction in brain volume ^[32] and enlarged ventricles ^[33]. Cognitive decline may also be a result of age related reductions in the dopamine neurochemical system ^[34], which is believed to regulate the prefrontal cortex ^[28]. Patients with severe alternations of this system (e.g. in Parkinsons Disease) indicated deficits in numerous cognitive domains such as memory, verbal fluency and reasoning ^[27]. Unfortunately pharmacological agents (e.g.Levodopa), which increase dopamine levels in the brain, have not reduced the rate of cognitive decline. It is argued such medications cannot work fully due to fewer dopamine receptors in the prefrontal cortex as a result of the aging process ^[28].