Category learning and perceptual categorization in schizophrenia.

The aim of this study was to evaluate category learning in schizophrenia on tests of perceptual abstraction. Participants learned to categorize simple geometrical shapes. The categories were either well-defined (discrete categories, or DCs) or ill-defined (graded categories, or GCs). In DCs, the cues defining category membership can be verbalized in an all-or-none fashion, while in GCs they cannot be defined unambiguously. Three types of learning were used successively: serial presentation of category-exemplars, verbal description, and feedback. After the serial presentation, schizophrenia patients showed a deficit for GCs (p<0.005) but not for DCs (p = 0.98). After the verbal definition of GCs, the difference between schizophrenia patients and controls diminished (p = 0.09). Finally, after the feedback learning of GCs, a significant difference was observed again (p<0.0001), suggesting that schizophrenia patients were impaired in this learning paradigm. The GC-learning impairment after the serial presentation displayed a relationship with the score of the cognitive component assessed with the Positive and Negative Syndrome Scale (r = -0.66). In conclusion, these results suggest that the perceptual stage of abstraction is impaired in schizophrenia. This impairment can be partially compensated by instructions via top-down verbal processes.