Objective specification of tritanopic confusion lines using visual evoked potentials.

The minimum distinct border (MDB) between different isoluminant hues of a bipartite field was set subjectively by adjustment and then according to a 3-point rating allowing determination of the S-cone specific (tritanopic) axis. This rating was compared with visual evoked potentials (VEPs) generated by coarse, isoluminant gratings, modulated along the same chromatic axes. Psychophysically determined tritanopic gratings elicited monophasic onset VEPs with the longest latency for each subject. Departure from this axis produced additional earlier negative components (reflecting additional response mechanisms). Colour-selective VEPs can, therefore, objectively specify tritanopic confusion lines with a comparable degree of accuracy to MDB judgements.