The extrastriate symmetry response is robust to alcohol intoxication.
Abstract
Visual symmetry activates a network of regions in the extrastriate
cortex and generates an event related potential (ERP) called the
sustained posterior negativity (SPN). Previous work has found that the
SPN is robust to experimental manipulations of task, spatial attention,
and memory load. In the current study, we investigated whether the SPN
is also robust to alcohol induced changes in mental state. A pilot
experiment (N = 13) found that alcohol unexpectedly increased SPN
amplitude. We followed this unexpected result with two new experiments
on separate groups, using an alcohol challenge paradigm. One group
completed an Oddball discrimination task (N = 26). Another group
completed a Regularity discrimination task (N =26). In both groups
participants consumed a medium dose of alcohol (0.65 g/kg body weight)
and placebo drink, in separate sessions. Alcohol reduced SPN amplitude
in the Oddball task (contrary to the pilot results) but had no effect on
SPN amplitude in the Regularity task. In contrast, the N1 wave was
consistently dampened by alcohol in all experiments. Exploratory
analysis indicated that the inconsistent effect of alcohol on SPN
amplitude may be partly explained by individual differences in alcohol
use. Alcohol reduced the SPN in light drinkers and increased it in
heavier drinkers. Despite remaining questions, the results highlight the
automaticity of symmetry processing. Symmetry still produces a large SPN
response, even when participants are intoxicated, and even when symmetry
is not task relevant.