PERCEPTION OF CONTOUR: II. EFFECT OF RATE OF CHANGE OF RETINAL INTENSITY GRADIENT
KRESGE EYE INST DETROIT MI
Pagination or Media Count:
Effort was directed to ascertaining the nature of the retinal stimulus effective in producing the perception of an edge under certain simple conditions of photoic foveal vision. A method is described by means of which a distal stimulus is computed which, under the conditions of observation existing, will result in the desired proximal or retinal stimulus. The observer can project a small fiducial dot of light onto the distal stimulus to indicate where an edge, break, contour or discontinuity appears. The study indicated that subjective apparent intensity or brightness is not simply related to the intensity on the retinal and that expression of this phenomenon in terms of the classical concept of the Weber-Fechner fraction, Delta II, would result in a positive intensity gradient producing a negative brightness increment. The amount of energy decrement on the retina had little effect upon the appearance of an edge, and the rate of change of energy with respect to retinal distance was an unimportant factor in the production of edges. The second derivative was considered the lowest derivative of energy with respect to retinal distance of substantial significance for contour formation. A fundamental principle is stated to be that a doublet edge may appear substantially symmetrically distributed on either side of a point where the rate of change of the rate of change of intensity on the retina is maximal. The separation of this doublet edge will be smaller the greater the value of the fourth derivative of energy with respect to retinal distance.
- Anatomy and Physiology