THEORY AND MEASUREMENT OF VISUAL MECHANISMS XI. 01~1 FLICm~R WITH SUBDMDED FIELDS

When visual flicker is produced by passing vertical dark bars across an illuminated field 1 with fixed inclined opaque stripes on it, certain pronounced changes are induced in the properties of the flicker contour. 2' 8 Ordinarily, with image fields not subdivided, and regardless of whether flicker is produced by sectoring the light beam at a focus 4 or by the striped cylinder technic, the dependence of the contour for flicker recognition on the light-time fraction tL in the flash cycle is direct and simple. 5 The maximum flash frequency F to which the F -l o g I curve asymptotically rises declines rectilinearly with increase of tL; its abscissa of inflection (photopic "cone" segment) increases rectilinearly with tL; and the third parameter of the probability summation 6 describing the simplex F -log I curve, namely the standard deviation atloz i of its first derivative in log I, with F~,~. put = 100, is found not to change at all when tL is altered. (In certain cases, with most arthropods, 7 slight changes in the shape of the lower part of the curve arise as a consequence of the convexity of the surface of the eye, but this does not affect the essential generality of the previous statement.) Fundamentally, the behavior of the scotopic "rod" part of duplex F -log I contours is the same, but this may be obscured by the integrated overlapping of the "rod" and "cone" populations of neural effects, s With an obliquely barred field, however, and flicker produced by evenly