Rotational and translational motion interact independently with form

Do the mechanisms that underlie the perception of translational and rotational object motion show evidence of independent processing? By probing the perceived speed of translating and/or rotating objects, we find that an object’s form contributes in independent ways to the processing of translational and rotational motion: In the context of translational motion, it has been shown that the more elongated an object is along its direction of motion, the faster it is perceived to translate; in the context of rotational motion, it has been shown that the sharper the maxima of curvature along an object’s contour, the faster it appears to rotate. Here we demonstrate that such rotational form–motion interactions are due solely to the rotational component of combined rotational and translational motion. We conclude that the perception of rotational motion relies on form–motion interactions that are independent of the processing underlying translational motion.

► A skinny ellipse appears to rotate faster than a fat ellipse.
► Elongated objects appear to translate faster in the direction of elongation.
► These two form–motion interactions are independent.