Gary Hatfield has studied visual perception for more than three decades. His works include experimental studies of shape constancy, theoretical papers on perception, and philosophical studies of the fundamental concepts and theories of visual perception and cognition and their history. His work in the history and philosophy of psychology extends from the seventeenth century to current controversies on qualia and perceptual representation. He has published books on Descartes and the Meditations and The Natural and the Normative: Theories of Spatial Perception from Kant to Helmholtz, and he has translated Kant's Prolegomena to Any Future Metaphysics. He is the co-founder of the Visual Studies undergraduate program at the University of Pennsylvania and has co-taught, with psychologists and art historians, courses and seminars on all aspects of visual perception.