Figure 1.

Effect of modafinil versus placebo relative to frequency of methamphetamine (MA) use on tests of inhibitory control and processing speed/attention. Vertical dashed lines represent the change in performance between the modafinil and placebo conditions for each participant, and the arrows indicate whether performance went up or down in the modafinil condition. CPT = Continuous Performance Test; ANT = Attention Networks Task (flanker task) incongruent reaction time (RT) minus neutral RT. Days of MA Use = days used MA on the 30 days before study entry. With the exception of Finger Tapping Scores, higher scores on each test represent worse performance. Fit lines were derived from the parameter estimates of the general linear mixed models described in the Results section. Note that a within-subjects design was used so that the same participants received both placebo and modafinil. On each test, individuals who had a greater frequency of baseline MA use showed an enhanced cognitive effect of modafinil relative to those with lower frequency of baseline MA use. All interactionps ≤ .05, with the exception trend-level significance with the ANT (p = .08).