Attention is a vital component of everyday functioning, and deficits in attention feature in many psychological disorders. Improved understanding of attention may eventually be critical to early identification and treatment of attentional deficits. One step in that direction is to acquire a better understanding of genetic associations with performance on a measure of reflexive visual attention. We have previously studied the relationship between selected genes and mean RT. This thesis reports on a new analysis of the same data which were used to examine mean differences but now examines the contributions of genetic markers to RT variability. I consider the relationship between mean RT and RT variability and account for other potential predictors of RT variability such as age, ethnicity, and sleepiness. I ask, after accounting for other reasons that RT variability might be increased in some subjects, does increased RT variability depend also on genotype?