This test is similar to the written version of the Pyramid and Palm Trees Test (Howard & Patterson, 1992). Unlike that test and the similar Camel and Cactus Test (Bozeat et al., 2000), which combine trials requiring similarity judgments with trials requiring thematic associations, our version uses only similarity judgments. Our version also evaluates knowledge about abstract concepts that cannot be easily depicted, and thus allows a comparison between concrete object and abstract concept knowledge. Behavioral and neurophysiological studies indicate substantial differences in the processing of abstract and concrete concepts (Binder et al., 2005; Kounios & Holcomb, 1994; Paivio, 1971; Sabsevitz et al., 2005; Wise et al., 2000), and neuropsychological evidence for sensitivity to this factor in aphasia (Coltheart et al., 1980; Goodglass et al., 1969; Katz & Goodglass, 1990; Roeltgen et al., 1983). In addition to overall accuracy, category specificity is measured by comparing performance on various superordinate categories, and task “difficulty” is manipulated using similarity distance ratings obtained from healthy controls (Sabsevitz et al., 2005).
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