Repetition related ERP effects in a visual object target detection task.

ERP responses to initial and repeated presentations of possible and impossible objects were recorded from 61 recording sites in a simple target detection task. In Experiment 1, the non-target objects were line drawings of possible and impossible 3-D geometric figures and the targets were line drawings of familiar everyday objects or combinations of parts of everyday objects. In Experiment 2, the non-target objects were everyday objects and the targets were possible and impossible 3-D geometric figures. In both experiments, at frontal sites, the repeated possible and impossible non-target items elicited less negative ERP waveforms relative to first presentations between 250 and 350-400 ms. At parieto-occipital sites, in both experiments, the repeated possible and impossible non-target items elicited less positive ERP waveforms than did first presentations beginning at about 300 ms. The briefly reduced frontal negativity to repeated items is consistent with familiarity arising from a facilitation of access to conceptual, semantic and visuo-spatial representations during object categorization. The polarity of the parieto-occipital effect was the reverse of what is usually found in stimulus repetition tasks, although it is consistent with earlier work using similar visual stimuli. It is interpreted as reflecting the availability of a newly formed representation (i.e., token) of the object just experienced.