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P. Satgunam, N. Fogt; The effect of target color on saccadic latency . Invest. Ophthalmol. Vis. Sci. 2004;45(13):2514.
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Purpose:The saccadic latency or reaction time can affect the efficiency of visual search. Saccadic latency is affected by both target luminance, and contrast. However, the influence of color on saccadic latency is not well established. The purpose of this study was to compare the saccadic latencies for red, green and blue targets at different eccentricities. Methods:Six color vision normal subjects (5 emmetropes and 1 low myope) participated. Measurements were made monocularly. Subjects were placed on a bite bar 53 cm from a computer monitor. Each subject first matched the luminance of the three target colors to the grey background. The luminance matched values were fed into a computer program to generate the colored saccadic targets (1.4º squares). For the saccadic latency measurements, subjects looked at a central fixation cross (0.53º) and then moved the eyes to a saccadic target when it appeared. The color, position (up, down, left or right), and eccentricity (1.9º to 11.7º horizontally and 1.9º to 7.1º vertically) of each saccadic target was randomly selected. After each target presentation, an auditory cue signaled the subject to return fixation to the central cross. Four subjects performed 216 trials, and 2 subjects performed 72 trials. Eye movements were measured using a scleral search coil. Results: The mean horizontal saccadic latencies were 326 + 79ms for the red targets, 334 + 72ms for the green targets and 350 + 91ms for the blue targets. The mean vertical saccadic latencies were 327 + 89ms for the red targets, 329 + 82ms for the green targets and 350 + 88ms for the blue targets. Two–way ANOVA showed that target color had a significant effect on latency but target eccentricity did not. Pairwise comparisons showed a significant difference in latency for the red and blue targets. No significant difference was found among the other color pairs Conclusions:Subjects were able to generate saccades to these colored targets in spite of the lack of luminance contrast. The latencies were longer than those typically reported (180ms–200ms), probably because the superior colliculus is important for generating saccades but has limited or no response to color. The increased latencies for the blue target when compared to the red target is in accordance with psychophysical studies where the kinetics of the blue cone mechanism is found to be slower than the red and green cone mechanisms. Because target eccentricity had no influence, the delays in the blue cone mechanism were the same regardless of the site of retinal stimulation.
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