Participants' representations of the concept human were examined to differentiate three types of associations between concepts and their component attributes: the capacity of concepts to cue attributes (attribute accessibility), the capacity of attributes to cue concepts (instance accessibility), and the extent to which attributes are thought of as central to concepts (attribute centrality), The findings provide information about the concept human itself and, more generally, about the functionally distinct roles those different attribute-concept associations play in guiding imaginative thought. College students listed attributes that differentiate humans from other animals, rated the centrality of those attributes, and listed animals that possess those attributes. Other students drew and described extraterrestrials that possessed some of the attributes that were found to vary across those listing and rating tasks, Rated centrality was the most important determinant of an attribute's impact on imaginative generation. When the imagined extraterrestrials were supposed to possess attributes that had been rated as central to humans (intelligence, emotional complexity, or opposable thumbs), participants projected more aspects of human form onto them than when the creatures were supposed to possess less central attributes or when attributes were unspecified.Man is distinguished from other animals by his imaginative gifts ... We are nature's unique experiment to make the rational intelligence prove itself sounder than the reflex.-Jacob Bronowski, The Ascent ofMan, 1973