Procesamiento léxico-semántico en pacientes con enfermedad de Alzheimer

Abstract

Alzheimer's disease presents as one of the first symptoms, alterations in the recovery and understanding of words. These deficits are not produced in all languages functions in the same way but well preserved and some longer than others. To find out what kind of words are the first to be deteriorated, in this work we have used reading tasks in which lexical and semantic process will be evaluated. Tasks stimulus are organized in relation to two psycholinguistic variables. On one hand, the age of acquisition (AoA), being one of the most studied and apparently one of the most influenced on the lexical and semantic process. On the other hand, imageability of words, because of being a semantic variable and to present patients with Alzheimer's disease, deficits in this type of process. Theoretical models in which this work is based are the model of the dual-route cascaded (Coltheart, Rastle, Perry, Langdon, & Ziegler, 2001) and connectionist models of Steyvers & Tenenbaum (2005), Monaghan and Ellis (2010) and Ellis and Lambón Ralph (2000). The study presented has two overall objectives. The first consists in comparing the influence of AoA variable in the lexical and semantic process in subjects with Alzheimer's disease with different degrees of deterioration. The second objective focuses on detecting if the AoA or imageability variable is which present a greater effect on AD in lexical process as cognitive impairment is higher. Three study groups were used: a control group consisting of 25 people over 55 years old who did not have cognitive deterioration or psychiatric history and two experimental groups consisting of 25 patients diagnosed with Alzheimer's disease with different degrees of deterioration (mild and moderate). To carry out the objectives of the work a battery of neuropsychological tests was used and three experimental tasks were designed. With respect to the experimental tasks, two of them were used to assess the lexical process and it was consisted of a variant of the lexical response called lexical selection task. Were used in this work, unlike the classical lexical decision task four stimuli in each experimental item: one target stimulus (words) and three distractors (pseudowords) In one of the tasks, the AoA variable was manipulated and the imageability of words in the other. The second experimental task consisted of a matching exercise defmition-word and evaluating semantic processing subjects. In this test a definition was presented and then four words: one target and three distractors semantically related. The target words are organized according to age of acquisition variable. In this case, the targets coincide with those used in the lexical selection task in which the variable AoA is manipulated. The results show a worse performance in the semantic task than in the lexical selection in both control groups as in Alzheimer subjetcs. These differences are progressively extended as the cognitive decline of the subject increases. Regarding the effect of the variable age of acquisition, maintenance of the pattern found in the control group (better performance in early words that in the later) is observed in Alzheimer's patients too, who are in the mild and moderate stages, differences increased with increasing cognitive impairment. Increased imageability effect with increasing cognitive impairment in subjects with AD. This effect is greater than recorded in the AoA in the two tasks of lexical selection. In summary, this work shows a greater preservation of lexical than semantic processing in subjects with both mild and moderate AD, with a more favorable early words than in the later performance. Furthermore, greater involvement of the semantic variables than lexical-semantic type in this kind of subject, an effect that increases as the cognitive impairment is higher.