WOLFGANG KöHLER Department of Psychology, Swarthmore College
It is the main purpose of this paper to discuss records of electric currents which have been taken from the heads of human subjects under conditions of pattern vision. We have recently turned to work in this field, because it seemed natural to do so in view of certain psychological observations. I will therefore first describe these psychological facts.
When visual objects, figures, dots, or lines have for some time occupied a given region of the field, other visual objects which are now shown in this region tend to be displaced or distorted. Phenomena of this kind are known as "figural after-effects." The objects which establish such effects are called "inspection (or I-) objects," and the objects which exhibit the effects, "test (or T-) objects" (13).
According to the definition of figural after-effects which has just been given, a T-object is affected only if it is located within or near the area in which the I-object has been shown. This area is defined in a retinal (or cortical) sense rather than in terms of "absolute" space. Suppose, for instance, that after the I-period the eyes of the subject turn to a new fixation mark. Under these conditions, an after-effect will be observed in the new direction if the retinal place of the T-object has the right relation to the retinal area previously occupied by the Iobject. The T-object need not differ from the I-object. When inspected for some time, many visual objects change their own spatial characteristics. In a way, they then serve both as I- and as T-objects.
Most figural after-effects can be derived from the following principle: T-objects recede from areas in which I-objects have been shown, particularly from the regions in which the contours of these objects have been located. As a result, T-objects may be simply dis-