Which Language Is More Affected in Bilinguals With Alzheimer's Disease? Diagnostic Sensitivity of the Multilingual Naming Test

Objective: This study examined the joint consequences of bilingualism and Alzheimer's disease (AD) for picture naming ability to determine which language is more affected by AD and what scoring methods best distinguish patients from controls. Method: Sixty-five Spanish-English bilinguals including 26 with dementia and 39 controls with equivalent age, education, and bilingual proficiency level, were tested on the Multilingual Naming Test (Gollan et al., 2012). Results: Bilinguals with AD named fewer pictures than controls, and overall AD seemed to affect both languages about equally, but exploratory analyses suggested that this varied with item difficulty. In the dominant language difficult items exhibited a larger effect of AD than easy items (which were at ceiling for both patients and controls), whereas in the nondominant language items of all difficulty levels were about equally affected by AD. An "either-language" scoring procedure (that counted items as correct if produced only in one of the two languages) increased naming scores especially in balanced bilinguals, and to an equal extent in patients and controls. Receiver Operating Characteristic analyses revealed that dominant language and either-language naming scores classified bilinguals as patients versus controls equally well and adding nondominant language scores did not improve diagnostic sensitivity. Conclusions: Testing primarily or exclusively in the dominant language is best for detecting AD naming impairments in bilinguals. However, AD affects the ability to access names in both languages, possibly for different reasons, and simple descriptions of language decline as "parallel" or "asymmetrical" (i.e., AD affecting one language more than the other) may be misleading in terms of the theoretical implications for bilingual language processing.