Wednesday, November 22, 2006

Book Review: Basic Vision

Imagine a textbook so engagingly written that you actually want to pick it up and read the next chapter. Such is Basic Vision: an Introduction to Visual Perception, by Robert Snowden, Peter Thompson, and Tom Troscianko. (Oxford University Press, 2006, ISBN-13: 978-0-19-928670-6.)

I’m in the habit of reading anything that catches my eye, and this attracted me with its fun illustrations and optical illusions. It kept me with its interesting, occasionally snarky, explanations of visual functions and dysfunctions.

This is the first textbook I’ve ever read cover-to-cover without being required to do so for a class. It is targeted toward university undergraduate students (and often addresses them directly), so it would probably not be of much use to a physician or other vision scientist who already has a solid understanding of eye-brain interactions. However, for the curious layperson, it is a wonderful introduction.

How do our eyes read a printed word? Not letter by letter as one might think, but by jumping back and forth and assembling the word from the length and shape of the letters. Substituting a nonsense word that has a similar shape to the real word will not impair reading as much as substituting a synonym or a word with the same meaning from another (known) language.

The effects of high and low spatial frequency (which sounds incomprehensible when you only read the words) were clearly illustrated by a pair of pictures. Both contained the image of a skull and the face of Sir Anthony Hopkins superimposed on one another, with their spatial frequencies reversed. So if you hold the book at normal reading distance, the left picture is a skull and the right is recognizably Sir Anthony Hopkins. But if you prop the book up and look at it from across the room, they have swapped places. It is tremendously spooky! And neatly explained in the text.

Another favorite example in the book shows the way depth perception involves an assumption on the part of the brain that light comes from above. One picture appears to show a carved wooden deer in relief. The other appears to show an upside-down carving of of another deer in intaglio. However, if you turn the book upside down, the raised deer appears sunken, and the sunken deer appears raised. And if you turn the book sideways, the perception of depth vanishes and you can clearly see that the two pictures are mirror images of each other, set side by side rather than along the plane of reflection in order to break that recognition.

I shant bore you with more details, however, if you wish I would or if you just want to see the illustrations I’ve described, I’ve provided a search box in the sidebar of this blog. Find out if a library near you has it. If not, see if they can get it through interlibrary loan. It will make you see sight in a whole different light.

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