An unusual case of after-imagery following fixation of an “imaginary” visual pattern

The case of a healthy normal subject is described in which negative after-images were reported to follow fixation of an “imaginary” pattern. The size of the after-image was measured at various distances and found to agree closely with the size of an after-image induced by fixation of a “real” visual pattern, and to conform roughly with Emmert's Law. No evidence for chromatic after-images was obtained. Two controls were conducted, one indicating that the results could not be attributed to after-images resulting from objective aids used to maintain an “imaginary” pattern of constant size; the other discounting the possibility of the subject's having guessed the correct values. Similar phenomena reported in the early literature are briefly mentioned, and some theoretical implications discussed.