Subjective and cognitive effects of alcohol
Results of the subjective effects scales and behavioural performance are shown in Figure 5. A minority of participants did not complete the subjective effects scales, so this analysis is based on 23/26 participants from the Oddball task and 24/26 from the Regularity task. Compared to placebo, alcohol made our participants feel less alert and more lightheaded. Other subjective effects were much less dramatic, with only a slight increase in contentment post experiment. This was confirmed by an Effect X Drink X Time interaction (F (8.324, 374.570) = 9.365, p < .001, ηp2 = 0.172) that was not further modulated by Task. The crucial Drink X Time interactions and pairwise differences between alcohol and placebo blocks are highlighted in Figure 5.
Discrimination between green and black stimuli in Oddball task was impaired by alcohol (F (1,25) = 7.359, p = .012, ηp2 = 0.227). Discrimination between symmetrical and random stimuli in the Regularity task was also impaired by alcohol (F (1,25) = 5.361, p = .029, ηp2 = 0.177). However, these differences only correspond to 1-2 additional error trials on average, and performance was typically near ceiling. Evidently, our 0.65 g/kg alcohol dose had modest emotional effects without impairing visual discrimination dramatically.