When does perceptual organization happen?

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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.