Previous work (Nagy & Thomas, 2003)
showed that signals in different Cardinal color mechanisms could be
combined to facilitate search for a color target. Further investigation
(Nagy et al., 2003) suggested that signals in
one Cardinal color mechanism were used to select a subset of stimuli to
be attended, while signals in second Cardinal mechanism were used to
discriminate the stimuli within the selected subset. In the studies
described below, we asked if observers could use color mechanisms tuned
to directions other than the Cardinal directions to select and
discriminate stimuli. Observers searched for a single target stimulus
that differed in chromaticity from nine distractor stimuli. A
two-alternative forced-choice procedure was used to estimate
thresholds. Results were consistent with the hypothesis that color
mechanisms tuned to many different directions in color space mediate
discrimination, but suggest that only signals in Cardinal mechanisms
can be used to select stimuli for attention.
Results imply that the selection of stimuli for attention on the
basis of color may be mediated at the level of the lateral geniculate
nucleus (LGN).