MIT's course 9.35, Perception, opens with instructor Josh McDermott laying out how the class will treat sensation and perception as a unified problem in cognitive science. He sketches the structure of the semester, moving from vision and hearing to the general computational and neural principles that let the brain turn raw sensory signals into a stable, useful model of the world. McDermott previews the kinds of questions the course will return to, such as why perception often feels effortless despite the ambiguity of the input, and how illusions expose the assumptions the brain is making. The lecture also covers logistics, readings, and problem sets, but its real content is the framing: what counts as a perceptual problem, and why studying vision and audition together clarifies principles that neither reveals alone.