Between-task exploratory analysis
These observations raise an important possibility: The fact that alcohol
had no effect on mean SPN amplitude in the Regularity task could be
partly due the fact that the participants had marginally (although
non-significantly) higher AUDIT scores in the Regularity task (Mean
AUDIT in Oddball task = 9.65 (SD =4.84); Mean AUDIT in Regularity task =
12.00 (SD = 3.96), t (50) = 1.911, p = .062, ds =
0.530).
Regression analysis supports this possibility (Figure 10). The DV was
alcohol-induced change in SPN amplitude. When entered alone, AUDIT
explained 17.8% of variance in the DV (R2 = 0.178, F
(1,50) = 10.818, p = .002). Inclusion of Task to the model explained
little additional variance (R2 change = 0.024, F
(1,49) = 1.466, p = .232). Given this analysis, we cannot confidently
claim that Task has an independent effect on alcohol induced changes in
SPN amplitude, beyond the effect of AUDIT.
Unfortunately, we did not obtain AUDIT scores from the 13 participants
in the pilot study. It could be that the pilot participants were
relatively heavy drinkers, explaining why alcohol enhanced the SPN in
this sample. This is plausible, considering that the maximum possible
AUDIT score is 40, and the pivot from SPN reduction to enhancement
happened at around 15 in the Oddball task.