When does perceptual organization happen?

Lead Research Organisation: University of Liverpool
Department Name: Institute of Psychology Health & Society

Abstract

Whenever our eyelids are open, an image is projected onto the retina at the back of the eyeball. But this can happen when we are unconscious. To see anything, the visual brain must organize and interpret the retinal image. Among other things, the visual brain must work out what features belong to the same object, how surfaces are arranged in depth, which surface features are caused by illumination and which by pigmentation. The visual parts of the brain are full of mechanisms which mediate perceptual organization. Our project will test WHEN the visual brain goes to the trouble of organizing and interpreting the retinal image.

At one extreme, our perceptual organization systems could be 'on red alert' whenever we are awake. Perhaps complete perceptual organization always happens, whether it is task-relevant or not? At the other extreme, perceptual organization systems might frequently default to 'stand by mode'. Perhaps perceptual organization is only undertaken when necessary, and the retinal image is often left uninterpreted?

Furthermore, perceptual organization might be robust or sensitive to changes in mental state. For instance, perceptual organization mechanisms might be disrupted by acute or chronic to alcohol consumption.

Visual symmetry is the perfect stimulus to answer these questions. First, we can precisely define and control the formal properties of abstract symmetrical patterns. Second, symmetrical patterns generate an Event Related Potential (ERP) called the Sustained Posterior Negativity (SPN). This neural signal has been well characterized, and it can be cheaply measured with scalp electrodes. The SPN is generated by known brain regions (V4 and LOC), and it can be used as a bio-marker of perceptual organization. If there is an SPN on the scalp, then perceptual organization has happened in the visual brain. Work package 1 will the discover the conditions for SPN generation: For instance, the SPN might be reduced when participants are attending to color or sound rather than symmetry.

Work package 2 will use functional Magnetic Resonance Imaging (fMRI) and advanced multi-voxel pattern analysis (MVPA) to assess changes to the visual symmetry code when participants attend to symmetry, color or sound. This can tell us how the symmetry representations in the visual cortex deteriorate when attention is directed elsewhere. Next, WP3, will use Transcranial Magnetic Stimulation (TMS) to assess the causal necessity of the different brain areas in automatic perceptual organization.

Finally our Work package 4 has an applied dimension. We want to discover how perceptual organization is altered by alcohol. Although alcohol is the most widely used an abused recreational drug in the UK, little is known about acute and chronic effects on perceptual organization. We will test the theory that alcohol reduces the speed of neural communication between the left and right visual hemispheres. We predict that the SPN response to vertical symmetry will be selectively delayed by mild intoxication, and in currently sober heavy drinkers. This has the potential to contribute to evidence based drink awareness campaigns, but it is only possible by building in the basic research in WP1-3. Ultimately, we will develop new research tool which anybody can download and use to measure alcohol-induced brain changes. This is important because the translation from basic to applied research in this area is often blocked by practical obstacles.

Our research team for this project is carefully chosen. Makin, Bertamini and Rampone are experts in symmetry perception, EEG recording and analysis. Prof Morland has extensive experience using fMRI to map the visual cortex. Silvanto is an expert on studying symmetry perception with TMS. Jones is a leading alcohol/EEG researcher at Liverpool, who is well placed to push the applied dimension of the project.

Planned Impact

Approximately 30% of adults in the UK regularly drink more than government recommendations, and alcohol costs the economy around £21bn per year. Importantly, most the attributable cost comes from heavy drinkers, rather than those with clinical dependence. Although drinking poses risks to their health in the future, these individuals are basically healthy (Alcohol Concern, 2013). We know that alcohol-related cues grab visual attention and are associated with craving and consumption. However there is still no consensus about how alcohol alters human vision.

This proposal includes both basic and applied research to fill this gap. The basic research is about the automatic nature of perceptual organization (Concentrated in Work Packages 1-3). Work package 4 will then build on these findings to examine the brain changes associated with acute and chronic alcohol use. This research is important because policy is often informed by claims about the safe limits of alcohol. For instance, over 2000 road deaths caused by alcohol happen every decade in the UK, and the legal blood alcohol limit was reduced to 50mg/ml in December 2014 (www.drinkaware.co.uk). However, even mild doses of alcohol could have consequential effects on vision.

Some research in this area has been rather descriptive and atheoretical, mainly documenting minor changes caused by mild intoxication. We will go beyond this and test the theory that alcohol reduces speed of neural transmission between the hemispheres, and thus slows integration of perceptual information across the corpus callosum (Kahn & Tmney, 2007). WP4 will examine the effects of 0.4g/Kg and 0.8g/Kg body weight doses on inter hemispheric communication speed.

We will take three concrete steps to maximize this impact.

First, we will develop an easy to use research tool for measuring alcohol induced disruption of inter-hemispheric communication. Once validated, this tool will be available on Open Science Framework, and promoted to likely user groups. We reasoned that the translational pathway from basic to applied alcohol research is often blocked because it is difficult for to measure alcohol induced brain changes without specialist equipment and analysis protocols. Our research tool will remedy this.

Second, we will run our usual visual properties driving visual preference workshop in 2020 and 2021, but with a special focus on alcohol and vision. This will foster links between both research camps, and allow us to showcase the downloadable research tool.

Third, this research will contribute public engagement and healthy drinking campaigns. We will communicate the results via the University of Liverpool press office. Furthermore, festivals such as Green Man and Cheltenham Science Festival allow alcohol consumption on site, so we will use these opportunities to highlight the way alcohol disrupts visual function. In the recent past we have had excellent success with similar projects in terms of academic impact (Journal Articles and Conference Presentations), media impact (both festivals are national and have substantial media presence) and individual impact (participants report awareness of drinking harms and increased motivation to reduce their consumption during feedback sessions).