THE DETECTION AND DISCRIMINATION OF CATEGORICAL YELLOW

Threshold detection of most spectral lights presented on a white backg round is subserved by colour opponent mechanisms which produce distinc t percepts of colours. Five ranges of wavelengths can be discriminated : red, yellow, green, blue and violet [Mullen and Kulikowski (1990) Wa velength discrimination at detection threshold. J. Opt. Sec. Am. A7, 7 33-742]. However, under most viewing conditions yellow can also be det ected and discriminated by activating the achromatic mechanism. Using 2-alternative forced-choice we studied detection and discrimination be tween spots (1 deg) which were either spectral colours or white (match ing the background in colour temperature), with and without masking th e achromatic mechanisms. For low colour temperatures of white (2700 K) , yellow could be discriminated from white at slight suprathreshold le vels of detection. However, at a colour temperature of 6800 K and with masking, the yellow-white discrimination threshold for 565-574 nm was also close to detection threshold (as for other wavelengths). We conc lude that it is possible to demonstrate the role of the blue-yellow op ponent mechanism in categorical perception of yellow (at threshold) by sensitizing its yellow branch and by suppressing the achromatic mecha nism. Copyright (C) 1996 The College of Optometrists.