Show each eye a different image, and your brain won't blend them — it alternates

When one eye is shown, say, a horizontal grating and the other a vertical one, you don't see a blurred mix of both. Instead your perception flips back and forth every few seconds, one image dominating, then the other, a phenomenon called binocular rivalry that's been used for over a century to study how the brain decides what becomes conscious.

— Randolph Blake, Nikos K. Logothetis, Binocular Rivalry — Nature Reviews Neuroscience, 2002