Eyes on the Brain

A neurobiologist explores the amazing capacity of the brain to rewire itself at any age

Do We See The Parts Or The Whole?

How do we recognize people and things so quickly?

Recently, I took the students in my introductory biology class on a field trip around the college campus. I taught them how to recognize different trees by their branching patterns, the presence of simple or compound leaves, and the shapes of buds and leaves. Ferns could be identified by whether or not they were “once, twice, or thrice-cut.” This is tedious stuff; it requires a lot of careful looking. Yet, if you ask naturalists how they identify trees so quickly and effortlessly, they often say that they recognize the tree by its overall look. How did they go from “keying” out the plant using specific characteristics to seeing the tree as a whole?

I spent the bulk of this summer in northern California which to me, a New Englander, was a foreign land. I decided to learn the names of the most common trees and did this by consulting a field guide and examining the shapes and arrangements of the needles or leaves, the cones on the conifers, the color of the bark, and so on. I found this hard to do. Yet, after a few weeks, all this study paid off. By mid-summer, while riding along in the car, I could easily spot the redwoods, the red firs, the blue gum eucalyptus, and more. I immediately saw the whole tree – not just its parts – or did I?

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I tried to observe myself as I was observing the trees and decided that I still identified trees by picking out certain details. With my first glance, I would notice a particular characteristic, such as the size and shape of the cones or the way they hung on the branch. Then, I would guess at the identity of the tree, looking for other features that confirmed or refuted my guess. All this happened so quickly and automatically that I had the sense that I hadn’t concentrated on the details at all but had, in one instant, seen the whole tree.

 I think the same sort of process happens when I recognize people. My husband Dan is very tall and lanky and mostly bald. Sometimes, I’ll look into a crowd and see a tall, lanky, mostly bald guy, and my heart will literally beat a little faster, and I’ll think - “Dan!” Then in the next instant, I’ll realized that I am looking at some stranger, not my husband. With that first glance, I had keyed into certain characteristics and come up with an hypothesis about the identity of the person. But I needed another perceptual instant to determine whether or not my hypothesis was true.

 

Susan R. Barry, Ph.D., is a professor of neurobiology in the Department of Biological Sciences at Mount Holyoke College and the author of Fixing My Gaze (June, 2009).

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