CONCLUSION

Early differences (50±65 ms) were observed between the ERPs elicited at posterior sites by task-irrelevant biological (male and female faces) and non-biological (hatched and grey shapes) stimuli in two conditions: in one, the stimuli from both categories were randomly presented in the same run, in the second, the stimuli from each category were separately delivered in distinct runs. This effect replicates results observed in a previous experiment [1], enhancing its reliability. However, these early differences (40±80 ms) were observed for geometrical figures only when the two shape categories were separated by salient visual characteristics. While these last findings can be explained by neuronal habituation and refractoriness-related phenomena in the visual cortex, the effects observed for face stimuli here (as well as for faces and hands in the previous experiment) may suggest the existence of coarse and automatic categorization processes for rapid distinction between two wide classes of stimuli with strong psychosocial or biological significance.