[Alzheimer's disease, category-specific impairment and relevant variables in object naming]

The study of the dissociations or category-specific effects between the domains of living beings and non-living beings in Alzheimer's disease (AD) is a controversial issue in the cognitive neurosciences. The lack of agreement among the different studies may be due to deficient control of certain cognitive and psycholinguistic variables that affect processing of the items.

To determine whether the presence of category-specific effects in AD can be caused by inadequate control of variables, such as the typicality or familiarity of the items. Furthermore, since the groups may contain different types of patients with opposing impairments (which would mask this kind of effect in the group analysis), both group and individual analyses were conducted.

A retrospective study was carried out to evaluate 66 participants (32 patients with AD) using a colour photo naming task with items controlled for seven disruptive variables.

No evidence of living/non-living dissociation was found in the analyses by groups, although the individual-based analysis did show some cases of category-specific effects.

Our data show that category-specific effects are not as widespread as they were believed to be and that the lack of control over the so-called disturbing variables may play an important role in studies on category-specific impairment. Our study also highlights the importance of conducting individual analyses in order to avoid overlooking certain effects that are masked in the group studies.