Brainstorm (1983)

Douglas Trumbull built this science-fiction thriller around a single switch. Everyday scenes play in 35mm at a near-square 1.66:1 with mono sound; whenever someone plays back another person's recorded sensations, the picture jumps to wide 2.2:1 65mm and the sound opens out into full stereo. The recordings feel like a bigger, louder world than the one the characters live in, which is exactly the point. The trade-off is that the effect loses much of its impact on a small screen, so find the widest letterboxed copy you can. It was also Natalie Wood's last film.