Abstract
We are examining the ability of spots versus gratings to reveal non-cardinal colors. Neurons in the LGN respond better to spots, while cortical neurons respond better to gratings (DeValois, Cottaris, Elfar, Mahon, & Wilson, 2000). In addition, non-cardinal mechanisms are known to not emerge until the cortex (Gegenfurtner, 2003). Thus, non-cardinal mechanisms should be more likely to be revealed with cortically-stimulating gratings than LGN-stimulating spots. This has been shown in the isoluminant color plane in macaque monkeys (Stoughton, Lafer-Sousa, Gagin, & Conway, 2012) and in the RG/LUM color plane in humans (Gegenfurtner & Kiper, 1992). Recent reviews of non-cardinal mechanisms (Eskew, 2009) and S-cone vision (Smithson, 2014) do not report that this has yet been examined in the TRIT/LUM color plane. We are filling in this gap by testing all three color planes, using both spots and gratings, in the same study and in the same species (human). Thresholds to detect spot or grating stimuli are measured in aligned or orthogonal speckled noise. For example, an orange/turquoise grating may be presented in orange/turquoise or purple/lime noise. Evidence for separate underlying neural mechanisms is seen when the threshold to detect the stimulus in aligned noise is greater than in orthogonal noise. All stimuli in the isoluminant plane are individually isoluminant via heterochromatic flicker photometry. Non-cardinal colors are created in equal threshold space. We aim to test 10 subjects in each color plane; preliminary results are largely following predictions.
Acknowledgement: National Science Foundation Grant No. BCS-1753808