In a nutshell: Attention and perception are separate brain processes. A tool commonly used to track one could actually be measuring the other.

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Neuroscience has long grappled with the relationship between attention and conscious awareness, or perception. Recent research from Brain Function CoE investigators suggests that the two processes are separate and use different pathways in the brain. This is illustrated by studies showing that we can be conscious of things we’re not paying attention to, and not conscious of things we are paying attention to.

Most research into conscious awareness has shown that becoming aware of an object leads to an increase in brain activity. This activity is commonly measured using steady-state visually evoked potentials (SSVEPs) from electroencephalography (EEG) recordings. SSVEPs are the brain’s response to visual stimulation at particular frequencies.

But new research from Brain Function CoE investigators questions whether SSVEPs are the right tool to use when studying awareness. The research team was led by Matthew Davidson and Naotsugu Tsuchiya from Monash University.

The researchers used EEG to record brain activity in people who viewed an optical illusion based on the concept of ‘perceptual filling-in’. This natural phenomenon occurs when objects in peripheral vision disappear and are replaced, or filled in, by features from the surrounding visual area.

In the experiment, the participants focused on a point in the centre of a computer screen. Four coloured circles also appeared on the screen in their visual periphery, and the participants were asked to note when the circles seemed to vanish. The researchers identified the brain activity corresponding to each circle by flickering the circle images at different frequencies and measuring the SSVEPs at those frequencies.

If SSVEPs tracked consciousness, then they should decrease when the participants believed that a circle had vanished. Instead, the researchers found that SSVEPs increased when a circle disappeared from consciousness.

Previous work showed that paying attention to visual targets in perceptual filling-in experiments increases the probability that they will disappear. Thus, the researchers concluded that what they and others have actually been recording using SSVEPs are changes in attention, not in consciousness.

This finding challenges long-held assumptions about the link between SSVEPs and visual consciousness. It is also further evidence that attention and consciousness are distinct brain processes.

Next steps:
The researchers are planning to investigate which areas of the brain are linked to attention and consciousness. They will do this by combining their experimental approach with techniques such as magnetoencephalography (MEG) and functional magnetic resonance imaging (fMRI).

Davidson, M. J., Mithen, W., Hogendoorm, H., van Boxtel, J. J. A., & Tsuchiya, N. (2020). The SSVEP tracks attention, not consciousness, during perceptual filling-in. eLife, 9, e60031. doi: 10.7554/eLife.60031

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