After-imagery in defective fields of vision.

In a study of visual after-images of patients with homonymous hemianopia one would anticipate an after-image only in that part of the field which is perceived by the patient during fixation. Fuchs (1920, 1921), however, found that such patients saw more in the after-image than in the stimulus field or the perceived field of vision. Thus Fuchs noted that a figure only partly seen on fixation (the remainder of the figure was not seen because it was situated in the blind part of the field) was perceived by the same patient in its entirety in the afterimage. This is known as the phenomenon of completion.t Using simple figures, such as circles and squares, Fuchs postulated that completion depended on the " inner structural requirements of the stimulus figures." On the other hand, Bender and Teuber (1946), who also studied completion effects in impaired fields of vision, and used complex figures such as an American flag in complementary colours, believed that these effects need not necessarily be explained only by qualities of the stimulus figure. They observed that the after-image may represent only partial tendencies toward completion. Thus additional areas seen in the after-image or the " completed areas " did not always produce a smoothing of contours or the completion of a total figure. Sometimes there occurred in the afterimage irregular additions to that which was perceived in the stimulus field. The present investigation was undertaken to study the nature of after-image alterations in a patient with irregular but homonymous defects in the-fields of vision following lesions in both occipital lobes. The test patterns used were simple geometric figures.