Sustained Posterior Negativity
The SPN was analysed in two a priori intervals (200-400 ms and 400-1000
ms). In the Oddball Task, SPN was reduced in the alcohol block (opposite
of the pilot results). In the Regularity task, The SPN was similar in
alcohol and placebo blocks. In both tasks, the SPN peaked at around 300
ms then declined.
Mixed ANOVA found a strong main effect of Interval (F (1,50) = 57.519, p
< .001, ηp2 = 0.535). The main effect of
Drink on SPN amplitude was not significant (F (1,50) = 1.171, p = .284,
ηp2 = 0.023). There was no Drink X Interval
interaction (F (1,50) = 0.288, p = .594, ηp2 = 0.006)
and no Interval X Drink X Task interaction (F (1,50) = 1.676, p = .201,
ηp2 =0.032).
There was also no Drink X Task interaction (F (1,50) = 3.601, p = .064,
ηp2 = 0.067). Despite this, we report the separate
pre-registered analysis on each task: There was a main effect Drink in
the Oddball task (F (1,25) = 5.724, p = .025, ηp2 =
0.186), but not in the Regularity task (F (1,25) = 0.272, p = .607,
ηp2 = 0.011).
Bayesian ANOVA confirmed the main effect of Interval (BF include
> 100). Other effects and interactions were mostly
inconclusive (BF include between 0.134 and 0.498). Bayesian pairwise
comparisons between alcohol and placebo in the late interval are
instructive, given that this was the important window in the pilot
study. There was no support for presence or absence of an alcohol effect
in the Oddball task (BF10 = 0.814). However, analysis supports theabsence of an alcohol effect in the Regularity task (BF01 =
4.631).
Overall, alcohol has no consistent effect on SPN amplitude. There was no
effect of alcohol on SPN amplitude in the Regularity task, and the
evidence from Oddball tasks is mixed, especially when considering the
contradictory pilot results. In contrast, alcohol reliably reduces N1
amplitude in all cases.