Habituated 5-mo-old infants to 3 types of visually presented rigid motion. Duration of fixation was the dependent measure. After reaching a criterion of habituation, a 4th rigid motion (not habituated) and a deformation were presented. Dishabituation was significantly greater to the deformation than to the 4th rigid motion. Comparison with a no-change control condition showed a significant difference for deformation when it followed the 4th rigid motion. It is inferred that the infants detected the invariant property of rigidity and differentiated it from the deformation. (18 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1978 American Psychological Association.