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As one works with color in a practical or experimental way, one is impressed by two apparently unrelated facts. Color as seen is a mobile changeable thing depending to a large extent on the relationship of the color to other colors seen simultaneously. It is not fixed in its relation to the direct stimulus which creates it. On the other hand, the properties of surfaces that give rise to color do not seem to change greatly under a wide variety of illumination colors, usually (but not always) looking much the same in artificial light as in daylight. Both of these effects seem to the due in large part to the mechanism of color adaptation mentioned earlier.
When the eye is fixed on a colored area, there is an immediate readjustment of the sensitivity of the eye to color in and around the area viewed. This readjustment does not immediately affect the color seen but usually does affect the next area to which the gaze is shifted, the longer the time of viewing, the higher the intensity, and the larger the area, the greater the effect will be in terms of its persistence in the succeeding viewing situation. As indicated by the work of Wright and Schouten, it appears that, at least for a first approximation, full adaptation takes place over a very brief time if the adapting source is moderately bright and the eye has been in relative darkness just previously. As the stimulus is allowed to act, however, the effect becomes more persistent in the sense that it takes the eye longer to regain its sensitivity to lower intensities. The net result is that, if the eye is so exposed and then the gaze is transferred to an area of lower intensity, the loss of sensitivity produced by the first area will still be present and appear as an u afterimagen super imposed on the second. The effect not only is present over the actual area causing the “local adaptation”，but also spreads with decreasing strength to adjoining areas of the eye to produce “lateral adaptation”. Also, because of the persistence of the effect if the eye is shifted around from one object to another, all of which are at similar brightness or have similar colors，the adaptation will tend to become uniform over the whole eye.
9. This selection is concerned primarily with .
A. the eye’s adaptation to color B. the properties of colored surfaces
C. the effect of changes in color intensity D. experiments on colored objects
10. Whether a colored object would, on two viewings separated in time，appear to the viewer as similar or different in color would depend mostly on •
A. the color mechanism of the eye in use at the time of each viewing
B. what kind of viewing had immediately preceded each of the viewings
C. the properties of the surface being viewed
D. whether the object was seen in artificial or natural light
11. If a person’s eye has been looking at an object in bright sunlight for some time，and then shifts
to an object not well lit — such as a lawn or shrub in shadow — we can expect .
A. a time lag in the focusing ability of the eye
B. the immediate loss of the “afterimage” of the first object
C. some inability to see colors of the latter-named objects until loss of sensitivity has been regained
D. adaptation in the central area of the eye but little adaptation in the lateral areas to the new intensity level
12. The present selection has apparently been preceded by some explanation of .
A. some experiments with color pigments B. the nature of color
C. the color properties of various surfaces D. the mechanism of eye’s adaptation to color