Adaptation, After-effect, and Contrast in the Perception of Tilted Lines. Ii. Simultaneous Contrast and the Areal Restriction of the After-effect

The preceding paper has reported the fact that visual lines undergo what may be termed adaptation followed by a negative after-effect with respect to their direction or orientation in the frontal visual field. A line possessing the characteristic of tilt appears to become less tilted during the course of a continued inspection, and thereafter a line objectively vertical or horizontal appears to be tilted in the opposite direction. In many respects the adaptation behaves like sensory adaptation of the sort exhibited by color and temperature. Furthermore the preliminary observations suggested that the negative after-effect behaved like a negative afterimage in being confined to the stimulated portion of the retina. It did not seem to produce any tilt of the visual field as a whole nor any disturbance in the subject's posture but was instead probably restricted largely to vertical and horizontal lines of approximately the same locus and visual angle as the tilted stimulus-line. In order to demonstrate that linear direction is functionally akin to a sensory process like that of color, two further investigations need to be made. It might be possible, first, to demonstrate the occurrence of simultaneous contrast in this type of perception. And second it should be shown conclusively that the process of adaptation is a localized process within the visual field. For if the vertical and 1 James J. Gibson and Minnie Radner, Adaptation, after-effect and contrast in the perception of tilted lines. I. Quantitative studies, this JOURNAL, 1937, ao, 453-467.