Event-related potential correlates of perceptual and functional categories: comparison between stimuli matching by identity and equivalence.

Event-related potentials (ERPs) correlates of two test criteria of an abstract category task were dissociated. In a stimulus equivalence task, 10 subjects observed pairs of figures presented serially in three conditions: reflexivity (generalized identity), equivalence (arbitrary derived relations from a previous training), and unrelated pairs. They were instructed to decide whether the second item in a pair matched or mismatched the first one. Participants' performance in reflexivity matching tests was faster and more accurate than in equivalence matching or mismatching responses. In the three conditions, an occipital P2, a frontal N2 and a parietal P3 ERP component were elicited. The earlier components P2 and N2 exhibited reflexivity matching effects, while the later component (P3) exhibited the only equivalence matching effect. In addition, the subtracted ERP components from unrelated minus identity and unrelated minus equivalence trials were computed within two time windows: 150-250ms (dN300) and 350-450ms (dN400). While both dN300 waves were not significantly different, the comparison of both dN400 waves showed statistical differences. Correlates of partially perceptual (but contextually abstract) concepts are elicited earlier than those of pure abstract concepts. These ERPs correlates of stimulus equivalence relation tests of semantic categories are in concordance with the behavioral data.