1 Mixed visual reference frames: perceiving non-retino-centric visual quantities in a retino-centric frame A.V. van den Berg 1 R. van Ee 2 and A.J.Noest 1 1 Functional Neurobiology, Helmholtz Institute, Faculty Biology, University Utrecht, Hugo R. Kruijtgebouw, Padualaan 8, 3584 CH Utrecht, The Netherlands 2 Physics of Man, Buys Ballot Laboratorium, Postbus 80000, 3508 TA Utrecht Correspondence should be addressed to A.V. van den Berg . E-mail: a.v.vandenberg@bio.uu.nl Tel: +3130 2534230/4218, Fax: +3130 2542219 Running title: Mixed visual reference frames Publication: Proc. SPIE Vol. 5666, p. 449-461, Human Vision and Electronic Imaging X; Bernice E. Rogowitz, Thrasyvoulos N. Pappas, Scott J. Daly; Eds. Publication Date: Mar 2005 Abstract 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 motion- or shape- sensitivity. In order to arrive at units that perform such a mixed transformation, the substructure of the retinotopic receptive field needs to be dynamically adjusted, using extra-retinal