Fig. 3. Correlation of λ and ψ with measures of arousal and reaction time. (A –F ) The point values for the coefficients λ or ψ (taken from fig. 2) are compared with measures of arousal and reaction time. In each case, the gray lines link the two drug levels, directed from low to high drug level. There was a strong relationship between arousal and λ (P = 0.005, A ), but not with ψ (P = 0.953, B ). Reaction time was instead strongly linked to ψ (P < 0.0001, D ), but not to λ (P = 0.895, C ). When new and old presentations of the images were considered separately, the ψ correlation remained strong for both (P = 0.001 and P = 0.0002, F ). There was no significant relationship between reaction time and arousal (P = 0.389, E ). Drugs are labeled as follows: D = dexmedetomidine; M = midazolam; P = propofol; T = thiopental; X = placebo.