Iris pigmentation and fractionated reaction and reflex time

Recent investigations indicate that an iris pigmentation-motor behavior relationship exists, but may be limited to the reaction time component of a motor task. The absence of differences in peripheral nervous conduction (Wolf and Landers, 1978) suggests that a central nervous system mechanism may be operating, possibly dependent on the characteristics of neuromelanin or catecholamine turnover. Experiment 1 tested this notion by fractionating simple reaction time into premotor and motor components by electromyography. ANOVA revealed that dark-eyed subjects had faster total reaction times and premotor times, but only the premotor time component approached significance (p < 0.07). Experiment 2 fractionated patellar reflex time of light-eyed and dark-eyed subjects into reflex latency and motor components. There were no eye color differences for any of the reflex time measures. The results of Experiments 1 and 2 support a central nervous system explanation for the iris pigmentation-reaction time phenomenon.