The effect of Alzheimer’s disease and aging on conceptual combination

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Brain and Cognition 59 (2005) 306–309 www.elsevier.com/locate/b&c

The effect of AlzheimerÕs disease and aging on conceptual combination Vanessa Taler a,b, Howard Chertkow a,c, Daniel Saumier a,c,* b

a Institut Universitaire de Ge´riatrie de Montre´al, Montre´al, Que., Canada H3W 1W5 ´ Departement de Sciences Biome´dicales, Universite´ de Montre´al, Montre´al, Que., Canada H3W 1W5 c Lady Davis Institute for Medical Research, Montre´al, Que., Canada H3W 1W5

Accepted 12 August 2004 Available online 12 March 2005

Abstract AlzheimerÕs disease (AD) subjects, healthy elderly, and young adults interpreted a series of novel noun–noun expressions composed of familiar object words. Subjects interpreted each item by selecting one of three possible definitions: a definition in which the referents of each noun were associated together in a particular context (e.g., rabbit cat: a cat that is raised by rabbits); a definition based on integrating the semantic attributes from each noun into a single referent (e.g., rabbit cat: a cat that has long ears and hops); and a semantic foil. The results show that the AD subjects selected significantly fewer integrational definitions and significantly more foils than healthy elderly subjects. Healthy elderly participants were also found to select significantly more foil definitions than the young adult subjects. These findings suggest that AD individuals have difficulty in integrating semantic features when interpreting novel noun–noun expressions and that both AD and healthy elderly individuals have morphosyntactic impairments related to the identification of the modifying and head nouns of noun–noun expressions. Ó 2005 Published by Elsevier Inc.

1. Introduction Impairments in semantic functioning in individuals with AlzheimerÕs disease (AD) have been well documented (for a review, see Whatmough & Chertkow, 2002). Their semantic impairments may be demonstrated in a variety of standardized tasks, including picture naming, verbal fluency (e.g., name as many animals as possible within a 1 min period), auditory probes (discrimination of true/false statements about objects), word-to-picture matching, and defining common object names. In contrast, healthy elderly individuals perform similarly to young adult subjects on such tasks, indicating that they have normal semantic functioning. While much effort has been devoted to investigating semantic memory functions in AD and elderly individuals, little

*

Corresponding author. E-mail address: [email protected] (D. Saumier).

0278-2626/$ - see front matter Ó 2005 Published by Elsevier Inc. doi:10.1016/j.bandc.2004.08.049

is known about how AD and normal aging affect the ability to form new semantic representations. The purpose of the present study is to explore the effects of AD and aging on the ability to form new conceptual representations of novel compound words. Novel noun–noun combinations require the integration of information about each of the composite nouns to achieve a coherent interpretation of the compound as a whole. Wisniewski (1996) posits that the nouns may be combined in one of two ways. First, the noun–noun expression may be interpreted by selecting an integrational interpretation, where a salient feature of the modifying noun (i.e., the first noun appearing in the noun–noun combination) is integrated into the representation of the head noun (i.e., the second noun of the noun–noun expression). For example, the combination ‘‘zebra horse’’ may be interpreted as a horse with stripes. On the other hand, an association process may be used whereby the referents of the modifying and head nouns are associated within the same context, but without feature integration. For example, the

V. Taler et al. / Brain and Cognition 59 (2005) 306–309

combination ‘‘zebra house’’ may be interpreted to mean a house in which zebras live. In the present study, AD subjects, healthy elderly individuals and young controls were required to match integrational and associative definitions to novel noun– noun expressions composed of familiar object words. Previous research suggests that the semantic errors of Alzheimer subjects occur because of mis-selection of a lexical entry due to featural competition among similar conceptual representations (e.g., responding ‘‘cat’’ to the stimulus lion; LaBerge, Balota, Storandt, & Smith, 1992), while associative errors (e.g., calling a pyramid a camel) occur rarely. It is therefore expected that AD subjects would be less likely to interpret novel noun–noun expressions in an integrational manner, while more frequently using associative definitions instead. We also tested whether AD individuals would show difficulties in correctly identifying the modifying and head nouns of noun–noun expressions. Finally, since there is substantial evidence indicating that semantic impairments do not occur as a result of normal aging, we expected healthy elderly adults would show similar patterns of performance when interpreting the noun–noun combinations.

2. Method 2.1. AD participants Ten AD patients were recruited from the Sir Mortimer D. Davis Jewish General Hospital Memory Clinic, a tertiary medical center referral clinic. Diagnosis of ‘‘probable AD’’ or ‘‘possible AD’’ was established according to diagnostic criteria for dementia according to the Diagnostic and Statistical Manual of Mental Disorders, Third Edition revised (DSM-III-R), and all subjects were diagnosed as having probable AD according to standard clinical criteria. Standard blood work and neuroimaging (CT or MRI) were also carried out, and the diagnosis was supported by abnormal performance on neuropsychological testing. Mean age and education of the AD participants were 81.9 (SD = 10.1) and 11.1 (SD = 11.1), respectively. Average Mini-Mental State Exam (MMSE) score was 23.8 (SD = 2.9). 2.2. Elderly and young adult controls Ten non-demented healthy and independently living elderly subjects (4 men and 6 women) served as agematched controls. Mean age and years of education were 77.2 (SD = 6.7) and 14.2 (SD = 2.0), respectively. There were no statistical differences between the AD and elderly control groups in terms of mean age [t (18) = 1.5, n.s.] or education [t (18) = 1.8, n.s.]. Ten young (5 men and 5 women; mean age 27, SD = 5.0) were also recruited for the study. The young subjects

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were all first year undergraduate students. The healthy elderly and young adult subjects were native speakers of English, and none had a history of neurological or psychiatric disease. 2.3. Stimuli Twenty novel noun–noun compounds were created using familiar object words. An equal number of natural (e.g., rabbit cat) and non-natural (e.g., book bicycle) noun–noun compounds were constructed for the stimulus set. We avoided using combinations of natural and non-natural concepts (e.g., igloo cat) in the set because integrative definitions tend to be less associated with the meanings of such compounds (Wisniewski, 1996) and we wished to obtained adequate numbers of such definitions from among the subjects. The entire set of noun–noun expressions included the following: news magazine, coconut tiger, violin guitar, canary bat, deer horse, mosquito fly, balloon ball, car bus, igloo tent, rabbit cat, book bicycle, couch sax, cup sock, hat boat, mouse squirrel, mirror scarf, apple duck, banana frog, cactus potato, and robin termite. Three possible definitions were constructed for each noun–noun combinations, one of which was a semantic integration interpretation, one of which was an associative interpretation, and one of which was a semantic foil whereby the modifying noun was taken to be the head noun. For example, for the stimulus rabbit cat, the integrational interpretation was ‘‘a cat that has long ears and hops,’’ the associative interpretation was ‘‘a cat that hunts rabbits,’’ and the semantic foil was ‘‘a rabbit that hunts mice and purrs.’’ Participants were asked to decide which of the three possible definitions best represented the meaning of each noun–noun item. Each noun–noun combination was presented in written form, along with its corresponding three definitions. Stimuli were presented in written form. In the case of AD patients, they were also read aloud to ensure comprehension. After completing the experiment, the AD subjects were given a picture–naming matching test to determine whether they correctly recognized the meanings of the words making up noun–noun expressions in the conceptual combination test. In this test, the subject were required to match each name comprising the conceptual combination expressions (40 names in all) to one of three black-and-white line drawings, one of which correctly corresponded to the target name. The words and pictures were presented on a series of pages in a random order.

3. Results All AD subjects performed at ceiling on the word–picture matching test. The results of the conceptual combina-

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V. Taler et al. / Brain and Cognition 59 (2005) 306–309

Fig. 1. Numbers of association, integration, and foil definitions selected by the AD, healthy elderly, and young participants.

tion test were analyzed in terms of the relative numbers of association, integrational, and foil definitions by the AD vs. healthy elderly groups, or by the healthy elderly vs. young control groups (see Fig. 1). The findings indicate that, while the AD subject selected similar numbers of association definitions (v2 (9) = 6.3, n.s.) as the healthy elderly subjects, they selected significantly fewer numbers of integrational definitions (v2 (9) = 31.3, p < .01) and significantly greater numbers of foil definitions (v2 (9) = 238.6, p < .01) as their elderly counterparts. Moreover, while the young healthy subjects selected similar numbers of association (v2 (9) = 11.4, n.s.) and integrational definitions (v2 (9) = 15.0, n.s.), the healthy elderly subjects selected significantly more foil definitions, than the young participants (v2 (9) = 35.0, p < .01).

4. Discussion As predicted, the results of thi...

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