RED-GREEN CHROMATIC DISCRIMINATION WITH VARIEGATED AND HOMOGENEOUS STIMULI

Chromatic discrimination thresholds were measured under conditions whi ch yielded fine and degraded discrimination seeps. Discrimination was assessed by identification of the location of one oi four homogeneous equiluminant stimuli arranged in a square or with pseudoisochromatic ( PIC) figures using the stimulus design of Regan, Reffin and Mellon (Vi s Res 1994; 34: 1279-1299). Stimuli were presented on CRT monitors and specified in units of cone trolands. They were viewed within a surrou nd metameric to the equal energy spectrum. L troland threshold versus retinal illuminance (TVR) functions were measured by four-alternative spatial forced-choice staircase procedures for (1) a four 1 x 1 degree s equiluminant stimuli arranged in a square and (2) 'C' shaped pseudoi sochromatic figures in which the observer had to identify the gap loca tion. The 'C' was constructed of spatially discrete patches of varying size and luminance to ensure that the observer's responses depended o n chromatic signals. The TVR functions appeared V-shaped and were simi lar for the two paradigms. The minimum occurred near the L excitation of equal-energy white. The PIC stimuli yielded poorer discrimination w ith the TVR function being displaced by similar to 0.5 log unit. Discr imination for stimuli degraded by luminance and spatial noise presente d within an achromatic appearing surround is sharpest near the chromat icity metameric to the equal energy spectrum. (C) 1998 Elsevier Scienc e Ltd. All rights reserved.