One Cause of Failure 167
(a) Regard a letter.
(b) Shift to a letter on the same line far enough
away so that the first is seen worse.
(c) Look back at No. 1 and see No. 2 worse.
(d) Look at the letters alternately for a few sec-
onds, seeing worse the one not regarded.
When successful, both letters improve and appear to move from side to side in a direction opposite to the movement of the eye.
(a) Look at a large letter.
(b) Look at a smaller one a long distance away
from it. The large one is then seen worse.
(c) Look back and see it better.
(d) Repeat half a dozen times.
When successful, both letters improve, and the card appears to move up and down.
Shifting by the above methods enables the patient to see one letter on a line better than the other letters, and, usually, to distinguish it in flashes. In order to see the letter continuously it is necessary to become able to shift from the top to the bottom, or from the bottom to the top, seeing worse the part not directly regarded, and producing the illusion of a vertical swing.
(a) Look at a point far enough above the top of
the letter to see the bottom, or the whole letter worse.
(b) Look at a point far enough below the bottom
to see the top, or the whole letter, worse.
(c) Repeat half a dozen times.