New research explores alcohol’s effects on extrastriate symmetry

Visual symmetry is fundamental to how we organize and recognize objects in our environment. Our brains can quickly and accurately detect symmetrical patterns, even when they appear in the periphery of our vision. In a new study published in Psychophysiology, researchers have found that while alcohol does influence certain brain activities related to visual perception, the ability to detect symmetry remains largely intact even when under the influence.

Previous studies have shown that our brains can quickly and efficiently detect symmetrical patterns, even under challenging conditions like visual noise or peripheral presentation. This ability is rooted in the extrastriate visual areas, which are specialized in recognizing and processing symmetrical patterns, contributing significantly to our perception of order and structure in our environment. However, most of these studies were conducted in controlled laboratory settings.

The researchers aimed to explore whether pharmacological changes, specifically alcohol consumption, could disrupt this symmetry perception. Given that alcohol inhibits the central nervous system and affects various cognitive and perceptual processes, they hypothesized that it might also impact how the extrastriate visual areas perceive and process visual symmetry.

“We were interested how robust our symmetry network in the visual system actually is. Previously we attempted to disrupt it by trying to over-load the visual system with a memory task. In the current study, we tried a psychopharmacological disruption,” explained study author Elena Karakashevska, a postgraduate researcher and a statistics tutor at the University of Liverpool.

In a pilot study involving 13 social drinkers, the researchers were surprised to find that alcohol appeared to enhance the brain’s response to symmetry. This unexpected finding suggested that alcohol might disinhibit the visual cortex, making it more sensitive to symmetry, a result that warranted further investigation and replication.

“With our pilot study, we observed that alcohol increases the perception of symmetrical images,” Karakashevska said. “This could’ve explained the ‘beer goggles effect’ or why people look more attractive to us after we have had a couple of drinks. Being good and sober scientists we replicated the study.”

To verify the pilot study’s findings, researchers conducted two new experiments with larger samples. The first, referred to as the Oddball task, involved 26 participants who discriminated between colors in symmetrical and random patterns. The second, the Regularity task, involved another group of 26 participants who discriminated between regular (symmetrical) and random patterns without considering color.

Participants were recruited from a university campus and were screened to ensure they had no history of alcohol or substance use disorders. They consumed a low-fat meal before each session and refrained from caffeine. Breathalyzer readings ensured zero alcohol consumption before the study. The alcoholic drinks contained vodka equivalent to 0.65 g/kg of body weight, while placebo drinks contained a no-alcohol substitute. Blood alcohol concentration (BAC) was measured throughout the sessions to monitor alcohol levels.

Participants sat 57 cm from a monitor displaying the visual patterns and completed the tasks while their brain activity was recorded using electroencephalography (EEG). The stimuli consisted of patterns with either 100% symmetry or random arrangements. Participants in the Oddball task reported the color of the patterns, while those in the Regularity task reported whether the patterns were regular or random.

The researchers found that, contrary to the pilot study, alcohol slightly reduced the brain’s response to symmetry in the Oddball task, rather than enhancing it. In the Regularity task, alcohol had no significant effect on the symmetry response. Despite these differences, all conditions produced a substantial symmetry-related brain signal, known as the Sustained Posterior Negativity (SPN), indicating that the visual system’s response to symmetry was robust under moderate alcohol intoxication.

Additionally, the study found that the N1 component of the brain’s response, which occurs earlier than the SPN, was consistently reduced by alcohol in both tasks. This reduction in the N1 component suggests that alcohol primarily affects early stages of visual processing rather than the later stages associated with symmetry perception. These findings indicate that while alcohol may slightly influence early visual processing, the overall perception of visual symmetry remains largely unaffected.

“It turned out that the initial results were a fluke, and alcohol doesn’t impact our symmetry perception, at least not in moderate doses in people who do not have alcohol dependency problems. The two main take-away messages are 1) always replicate unexpected results and 2) moderate alcohol doses do not impact our symmetry perception,” Karakashevska told PsyPost.

Interestingly, heavier drinkers showed an enhanced symmetry response under alcohol, while lighter drinkers showed a reduced response.

“Individual differences can partially account for the effects alcohol has on symmetry processing in the brain,” Karakashevska explained. “In our study, people who do not consume alcohol very often are more robust to alcohol disruptions on visual processing, compared to heavier drinkers. Despite this, we can confidently confirm that both light and heavy drinkers have the symmetry-related event-related potential.”

Future research could further explore these individual differences and investigate other types of visual regularities beyond symmetry, such as rotational or translational patterns. Additionally, studies could examine the effects of different levels of alcohol consumption and other substances to understand their broader impacts on visual and cognitive functions.

“Long term, we aim to expand the Liverpool EEG data catalogue and systematically test the robustness of the visual system, as well as promote open research and conducting well powered experiments,” Karakashevska said.

“I am a big advocate for practicing open and transparent science and measuring real effects,” she added. “This involves recruiting large samples and pre-registering predictions and analyses. Our study is an example of why this is important. We could have ran with the pilot results which make a good headline e.g. ‘EEG brain recordings explain why we find people more attractive when we are drunk,’ but we knew that good scientific practices trump catchy headlines, so we replicated the experiment.”

The study, “The extrastriate symmetry response is robust to alcohol intoxication,” was authored by Elena Karakashevska, Yiovanna Derpsch, Andrew Jones, and Alexis D. J. Makin.