144 Memory as an Aid to Vision
instead of simply remembering a period in their minds. This does them no good, but is, on the contrary, a cause of strain. The period can be imagined perfectly and with benefit as forming part of a black letter on the test card, because this merely means imagining that one sees one part of the black letter best; but it cannot be imagined perfectly on any surface which is not black, and to attempt to imagine it on such surfaces defeats the end in view.
The smaller the area of black which the patient is able to remember, the greater is the degree of relaxation indicated; but some patients find it easier, at first, to remember a somewhat larger area, such as one of the letters on the Snellen test card with one part blacker than the rest. They may begin with the big C, then proceed to the smaller letters, and finally get to a period. It is then found that this small area is remembered more easily than the larger ones, and that its black is more intense. Instead of a period, some patients find it easier to remember a colon, with one period blacker than the other, or a collection of periods, with one blacker than all the others, or the dot over an i or j. Others, again, prefer a comma to a period. In the beginning most patients find it helpful to shift consciously from one of these black areas to another, or from one part of such an area to another, and to realize the swing, or pulsation, produced by such shifting (see Chapter XV) ; but when the memory becomes perfect, one object may be held continuously, without conscious shifting, while the swing is realized only when attention is directed to the matter.
Although black is, as a rule, the best color to remem ber, some patients are bored or depressed by it, and prefer to remember white or some other color. A