This experiment asked whether infants at 5 months perceived an invariant over four types of rigid motion (perspective transformations), and thereby differentiated rigid motion from deformation. Four perspective transformations of a sponge rubber object (rotation around the vertical axis, rotation around the horizontal axis, rotation in the frontal plane, and looming back and forth) were contrasted with a rubbery "squeezing" motion of the same object. Twenty-four infants were habituated to three of the perspective transformations and tested on a pre- and post-test with a fourth perspective transformation and with the deforming motion. The dependent variable was looking time. Backward habituation curves showed a rise in looking time when the post-test was introduced after habituation, but a greater rise for the deformation than for the rigid transformation. Analysis of variance confirmed that the type of motion (rigid or deforming) was significant in determining degree of habituation. The inference was made that the infants perceived the invariant property of rigidity in all four perspective transformations and thus differentiated them from deformation. (Author/MS)