Department of Computer Science, The University of Texas at Austin, Austin, TX, USA.|Computer Science and Engineering, University of Michigan, Ann Arbor, MI, USA.|Center for Perceptual Systems, The University of Texas at Austin, Austin, TX, USA.|Department of Computer Science, The University of Texas at Austin, Austin, TX, USA.|Cognitive Science Center and Institute of Psychology, Technical University Darmstadt, Darmstadt, Germany.|Department of Computer Science, The University of Texas at Austin, Austin, TX, USA.|Center for Perceptual Systems, The University of Texas at Austin, Austin, TX, USA.