Mind Hacks

Hack #66. Trick Half Your Mind

When it comes to visual processing in the brain, it’s all about job delegation. We’ve got one pathway for consciously perceiving the world—recognizing what’s what—and another for getting involved—using our bodies to interact with the world out there.

The most basic aspects of the visual world are processed altogether at the back of your brain. After that, however, the same visual information is used for different purposes by two separate pathways. One pathway flows forward from the back of your brain to the inferior temporal cortex near your ears, where memories are stored about what things are. The other pathway flows forward and upward toward the crown of your head, to the posterior parietal cortex, where your mental models of the outside world reside. Crudely speaking, the first pathway (the “ventral” pathway) is for recognizing things and consciously perceiving them, whereas the second (the “dorsal” pathway) is for interacting with them. (Well, that’s according to the dual-stream theory of visual processing [[Hack #13]].)

The idea was developed by David Milner and Melvyn Goodale in the 1990s, inspired in part by observation of neurological patients with damage to one pathway but not the other. Patients with damage to the temporal lobe often have difficulty recognizing things—a toothbrush, say—but when asked to interact with the brush they have no problems. In contrast, patients with damage to the parietal lobe show the opposite pattern; they often ...