Impairment of homonymous processing in Alzheimer’s disease

Abstract

An important issue in research on language is how concepts are represented and associated with each other in the brain. Many investigations have focused on language ambiguity and the phenomenon of homonymy in which a single lexical item, presenting the same form, is related to different meanings. Our study aims to test the hypothesis that weak association of meaning characterizing homonyms may be especially prone to brain damage. To verify this hypothesis a test of attribution of the meaning of homonymous words, the Humpty Dumpty (HD) test, was applied to 50 patients with Alzheimer’s disease (AD) and 50 healthy subjects. Results show that AD patients are impaired in the HD test in an early phase of disease and that performance correlates with naming ability and phonological fluency. The data are in keeping with a growing body of literature that supports dual impairment to the semantic system in AD, i.e., to semantic knowledge and active processing and access to the semantic field. The evaluation of the ability to resolve homonymous ambiguity, using the HD test, may provide a useful and quick clinical tool to detect the anomalies of the semantic network linked to either a loss of the core system where meaning of words is stored or an impairment of the access to an intact semantic representation.

Appendix: Instructions

“Now I will tell you a word that can have more than one meaning. For example, the word Cappuccino can either mean a drink or a monk. It is not important to give the best definition, but I want you to understand and explain the meaning of a word in every possible way, such as using other words, gestures, or even sketching it if you need to. For instance the word vite means …” (the subject is encouraged to indicate the possible meanings). “I would like you to find at least two meanings for each word that I am going to tell you”. If necessary you can provide the subjects with more examples until the comprehension of the task is clear. It is also explained that only the meanings strictly related to the words themselves are considered valid. The examiner writes down all the answers given by the subjects, but credit is not given for answers such as plurals (e.g., vite [screw] which is the plural of vita [life]) or declinations of verbs (such as lotto [lot, site] which is a form of the verb lottare [to fight]) nor are proper names taken into consideration (e.g., lotto [Lorenzo Lotto] as the Italian painter or capitale [Capital] as a work by Karl Marx).

Valid answers to each word (the percentage of valid answers given by control subjects is showed in brackets).

Homonymous words	Dominant meaning	Subordinate meanings
Rombo	Geometric shape (90.6 %) [rhombus]	Fish (40 %), [turbot] Noise (23.7 %) [rumble]
Articolo	Part of a speech (84.3 %) [article]	Merchandise for sale (70 %) Writing about something (39.4 %), [article] Legislative law (7.5 %), [article] Element of a religious doctrine (0 %) [article]
Miglio	Plant used as animal feed (82.5 %) [millet]	Measure unit for distance (81.2 %) [mile]
Batteria	A set of elements (90.6 %) [set]	Musical instrument (85 %) [drums] Infantry section (16.9 %) Chicken cage (3.7 %) Round of a sport tournament (1.9 %)
Lotto	Game (97.5 %)	Amount of wares, part of a whole (76.2 %)
Scorta	Body guards (94.4 %)	Stockpile (86.2 %)
Capitale	Holdings (93.1 %)	Main city of a country (85 %)

Percentage of subjects that produced the dominant meaning in the HD test

Homonymous word	Dominant meaning
	Controls (%)	AD (%)
Rombo	90.6	59
Articolo	84.6	a
Miglio	82.5	69
Batteria	90.6	91
Lotto	97.5	95
Scorta	94.4	62
Capitale	93.1	88

1. ^aThe majority of patients (62 %) retrieved one of the subordinate meanings of the word—“merchandise for sale”—rather than the first option—“part of speech”