A meta-analytic review of category naming in Alzheimer's disease
Patients with Alzheimer's disease (AD) experience word-finding difficulties that become increasingly pronounced as pathological changes accrue in the brain. One question that has received increasing attention over the last two decades concerns whether the anomia in AD is category-specific, i.e. differentially affects the ability to name living things (LT) and non-living things (NLT). The current meta-analysis systematically reviewed the effect sizes for naming pictures of LT and NLT in comparisons of AD patients and healthy controls in 21 studies with over 1000 participants (557 patients and 509 healthy controls). A random effects model analysis revealed no significant difference in the large weighted effect sizes for naming pictures of LT and NLT (d = 1.76 and 1.49, respectively). Moderator variable analyses revealed a significant impact of stimulus colour on the effect size for LT, indicating that using colour stimuli significantly increases the impairment of naming LT in AD patients. Additionally, we found that LT and the NLT effect sizes were larger for samples with proportionally more female patients; smaller samples produced larger LT effect sizes. In contrast, effect sizes were not significantly related to dementia severity, patient age, the number of stimuli, years of education, or the number of matching variables controlled.