A within-modality test of semantic knowledge: The Size/Weight Attribute Test

Individuals with semantic dementia (SD; n=12) or Alzheimer's disease (AD; n=20) and healthy volunteers (n=40) were tested on tasks probing attribute rather than associative knowledge of animals and objects in the visual and verbal domains. The tasks were within modality, in that they probed knowledge in a single presentation modality (pictures or written words) and did not require cross-modal matching. Participants were required to make the same simple judgment about triads of animal stimuli ("Which is the largest and smallest?") and object stimuli ("Which is the heaviest and lightest?"). Control participants scored at ceiling on this simple task. Overall, the SD patients were significantly more impaired on this task than were the AD patients, who in turn were significantly more impaired than the controls. There was a strong trend for SD but not AD patients to show worse performance with verbal than visual material. However, no significant effects of category were found in either patient group. The Size/Weight Attribute Test has the potential to assess modality-specific deficits of semantic knowledge.