Imagine the table where you've eaten the most meals. Form a mental picture of its size, texture, and color. Easy, right? But when you summoned the table in your mind's eye, did you really see it? Or did you assume we've been speaking metaphorically?
As it turns out, how people form mental images seems to vary significantly, a fact that's surprised those who've encountered it for more than a century. In 1880, Francis Galton published his classic paper "Statistics of Mental Imagery" after asking a series of subjects about images summoned by their minds. Some protested that they couldn't really see anything. "These questions presuppose assent to a proposition regarding the 'mind's eye' and the 'images' it sees," one subject wrote. "This points to some initial fallacy … It is only by a figure of speech that I can describe my recollection of a scene as a 'mental image' which I can 'see' with my 'mind's eye' ... I do not see it any more than a man sees the thousand lines of Sophocles which under due pressure he is ready to repeat. The memory possesses it."
Yet others described a strikingly different capacity:
Many men and a yet larger number of women ... declared that they habitually saw mental imagery, and that it was perfectly distinct to them and full of color. The more I pressed and cross-questioned them, professing myself to be incredulous, the more obvious was the truth of their first assertions. They described their imagery in minute detail, and they spoke in a tone of surprise at my apparent hesitation in accepting what they said. I felt that I myself should have spoken exactly as they did if I had been describing a scene that lay before my eyes, in broad daylight, to a blind man who persisted in doubting the reality of vision.
He then described how people with a talent for mental imagery see things in their mind's eye:
1. Brilliant, distinct, never blotchy.
2. Quite comparable to the real object. I feel as though I was dazzled, e.g., when recalling the sun to my mental vision.
3. In some instances quite as bright as an actual scene.
4. Brightness as in the actual scene.
5. Thinking of the breakfast table this morning, all the objects in my mental picture are as bright as the actual scene.
6. The image once seen is perfectly clear and bright.
7. Brightness at first quite comparable to actual scene.
8. The mental image appears to correspond in all respects with reality. I think it is as clear as the actual scene.
9. The brightness is perfectly comparable to that of the real scene.
10. I think the illumination of the imaginary image is nearly equal to that of the real one.
11. All clear and bright; all the objects seem to me well defined at the same time.
12. I can see my breakfast table or any equally familiar thing with my mind's eye, quite as well in all particulars as I can do if the reality is before me.
Until reading this paper, I'd never imagined that other people have a much higher capacity than I do to form a mental image. Now I suspect that they do. Indeed, I don't even understand what it is to imagine something with "brightness." My breakfast table is bright when the sun shines in through the windows and dim in the dead of night. Shouldn't its brightness depend on when I conjure it? Yet a man without this capacity said, "Dim and not comparable in brightness to the real scene." To what extent, I wonder, was he speaking metaphorically?