Mixed visual reference frames: perceiving nonretino-centric visual quantities in a retino-centric frame

It is a useful competence to see motion relative to the head or to the external world, although those quantities are not directly given on the retina. The same holds for judgement of the shape of an object. We argue that the required transformations can be and are done independent of the associated direction transformations. This creates perceptual channels with retinal apertures but non-retinocentric motionor shape-