If you look in standard physiology and psychology textbooks, you will learn that a sketch is effective because cells in your primary visual cortex, where the earliest stage of visual processing occurs, only care about lines. These cells respond to the boundaries and edges of things but are insensitive to the feature-poor fill regions of an image. This fact about the circuitry of the primary visual area is true, but does it explain why a mere outline sketch can convey an extra vivid impression of what’s being depicted? Surely not. It only predicts that an outline sketch should be adequate, that it should be as effective as a halftone (the reproduction of a black-and-white photo). It doesn’t tell you why it’s more effective.
A sketch can be more effective because there is an attentional bottleneck in your brain. You can pay attention to only one aspect of an image or one entity at a time (although what we mean by “aspect” or “entity” is far from clear). Even though your brain has 100 billion nerve cells, only a small subset of them can be active at any given instant. In the dynamics of perception, one stable percept (perceived image) automatically excludes others. Overlapping patterns of neural activity and the neural networks in your brain constantly compete for limited attentional resources. Thus when you look at a full-color picture, your attention is distracted by the clutter of texture and other details in the image. But a sketch of the same object allows you to allocate all your attentional resources to the outline, where the action is.
FIGURE 8.1 Comparison between (a) Nadia’s drawing of a horse, (b) da Vinci’s drawing, and (c) the drawing of a normal eight-year-old.
Conversely, if an artist wants to evoke the
Great artists intuitively tap into the law of isolation, but evidence for it also comes from neurology—cases in which many areas in the brain are dysfunctional—and the “isolation” of a single brain module allows the brain to gain effortless access to its limited attentional resources, without the patient even trying.
One striking example comes from an unexpected source: autistic children. Compare the three illustrations of horses in Figure 8.1. The one on the right (Figure 8.1c) is by a normal eight-year-old child. Pardon me for saying so, but it’s quite hideous—completely lifeless, like a cardboard cutout. The one on the left (Figure 8.1a), amazingly, is by a seven-year-old mentally retarded autistic child named Nadia. Nadia can’t converse with people and can barely tie a shoelace, yet her drawing brilliantly conveys the
The answer comes from the law of isolation as well as the brain’s modular organization. (Modularity is a fancy term for the notion that different brain structures are specialized for different functions.) Nadia’s social awkwardness, emotional immaturity, language deficits, and retardation all stem from the fact that many areas in her brain are damaged and function abnormally. But maybe—as I suggested in my book