Your brain, in some ways, is really several brains trying to agree on one account of the world. Sometimes those many brains don’t agree, and they produce confusion — or an illusion. At her wonderful Biophemera, Jessica Palmer uses a review of new book by Roberg Kurzban, to look at how this works.

Psychologist Robert Kurzban’s new book promises to explain Why Everyone (Else) Is a Hypocrite.It’s a bold promise, and I was skeptical when first invited to review it. But Kurzban delivered – hilariously, entertainingly so. Although since I agree with almost everything he writes, I may not be the most objective of critics. (FYI: this is a long review, so if you’re short on time, you can skip to the end of the post, and watch the author’s short video trailer about the book. Cheers.)

For starters, Kurzban has convinced me to be more careful when I talk and write about my brain (and yours). Kurzban’s key point is that our brains are modular. As a result of this modularity, different cognitive units can know or believe inconsistent things at the same time. Kurzban illustrates this idea with the Adelson illusion – in my opinion, one of the best optical illusions ever. Here it is:

Believe it or not, square A is exactly the same color as square B!

Most people have a difficult time believing this – I certainly do. But Adelson’s illusion is a simple application of lightness (or color) constancy: our visual system is designed to feed us not just raw data, but a useful interpretation of what we see. This auto-correction process allows the pages of a book to appear “white” in both bright sunlight and leafy shade, despite the change in the amount of light reflected from the pages. (You can prove to yourself that your visual system is deceiving you by framing squares A and B with your fingers, to isolate them from the rest of the image and establish a common reference color.)

For more confounding wonders, read the whole review at Biophemera, where Palmer has also posted a video interview with Kurzban.