Michael Crichton was all wrong—he had his fictitious T. rex crippled with a crude exclusively motion-based visual system, a kind of dumb killing machine. Some recent work on reconstructing the brain of T. rex with CT scans of fossils suggests otherwise. Instead, while definitely not a brilliant thinker, what the animal had was elaborate multimodal sensory processing systems.

In the top panel of this picture, you can see were the brain is located in the skull; relatively tiny and buried deep, isn't it? The lower panel is the reconstructed brain, and what you can see is that the olfactory bulbs at the anterior end are relatively large, so it likely had a very good sense of smell. The inner ear structures are also large, so it probably had excellent hearing and a good sense of balance, a sign of an active animal.

CT scans of T. rex's brain (blue) reveal sizable olfactory bulbs (red arrow) and an inner ear (red) with long, delicate canals for balance and cochlear duct for hearing.

Other analyses of its visual system also reveal that its vision was sharp.

T. rex, with its forward-facing and widely separated eye sockets, turned out to have great binocular vision and, likely, depth perception. When T. rex dipped its head about 10°—similar to the angle of the alert posture that Witmer estimated—it would have maximized the width of its binocular field of view at 55°, as good as that of hawks, Stevens says. That's not quite as good as those of the highly birdlike dinosaurs, such as Troondon, but it exceeds that of other adult tyrannosaurids.

There is still some debate over Horner's proposal that T. rex was a scavenger, and these observations don't resolve that, since scavengers also need good sensory systems. That it may have had an unusually good sense of hearing, though, inclines me towards the big predator hypothesis.

Stokstad E (2005) Tyrannosaurus rex Gets Sensitive. Science 310(5750): 966-967