No category specificity in Alzheimer's disease: a normal aging effect

Area of Science:

• Neuropsychology
• Cognitive Neuroscience
• Gerontology

Background:

• Category effects, where performance differs across semantic categories, are studied in cognitive tasks.
• Previous research suggested category disadvantages in Alzheimer's disease (AD) patients, particularly for living things.
• Potential confounding factors and ceiling effects in control groups can complicate interpretation.

Purpose of the Study:

• To investigate category effects on picture naming, naming to definition, and word-picture matching in Alzheimer's disease (AD) patients.
• To determine if observed category effects in AD are intrinsic to the disease or attributable to general cognitive decline.
• To compare category effects in AD patients with those in age-matched healthy elderly controls.

Main Methods:

• 38 AD patients and 30 elderly controls performed three category-matched tasks.
• Tasks were controlled for nuisance variables known to differ across semantic domains.
• Bootstrap analyses of covariance were used, with control performance as a covariate to address ceiling effects.

Main Results:

• Standard analyses showed category disadvantages for living things in both AD patients and controls.
• Covariate analyses controlling for control performance eliminated significant category effects in AD patients across all tasks.
• Control performance accounted for a substantial portion of the variance in AD performance (42-64%).

Conclusions:

• Category effects observed in Alzheimer's disease (AD) patients on these tasks do not appear to reflect intrinsic disease-specific variables.
• The magnitude and direction of category effects in AD patients are comparable to those found in healthy elderly individuals.
• Task difficulty and general cognitive status, as reflected by control performance, are critical factors in understanding category effects in AD.