Blink and you’ll miss it


In a nutshell: A new method for measuring rapid brain activity helps to explain why our brains can’t process many things at once.

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Blink and you’ll miss it

When people are asked to monitor a rapid stream of images for two target objects, they will almost always spot the first target. However, if the second target is presented soon afterwards – as little as 200–500 milliseconds later – they will often have no conscious awareness of it. It’s as if their attention has blinked and missed it.

Neuroscientists thought that this phenomenon – known as ‘attentional blink’ – might be a result of the brain reaching the limit of its attention capacity. But it was difficult to study in detail, because brain imaging methods weren’t sensitive enough to measure activity at such short time scales.

A research team led by Brain Function CoE researcher Matthew Tang, then in Jason Mattingley’s group at the University of Queensland and now at Australian National University, developed a new experiment and imaging method to look at what happens in the brain during attentional blink.

The researchers showed participants a rapid stream of images on a screen. All the images featured parallel stripes pointing in different directions. In the two target images, the stripes were narrower and closer together. While the participants watched the screen, their brain activity was monitored using electroencephalography (EEG) – a non-invasive brain monitoring technique. After they had viewed all the images, they were asked to report the direction of the stripes in the two target images – either by remembering or by guessing.

The researchers found that participants’ recollection of each target was affected not just by the target itself, but also by images they saw immediately afterwards. This suggests that as soon as we pay attention to something, the brain starts to integrate the visual information that follows, even if it is not relevant.

Thanks to their new experimental approach, the researchers were able for the first time to determine which images the brain was processing. They did this by combining statistical analyses with the EEG recordings to decode the direction of the stripes in each image. When participants recalled the second target correctly, the researchers could accurately decode the direction from the EEG recording. However, when participants missed the second target, the quality of the decoding was significantly worse, even poorer than for non-target images.

Based on their results, the researchers believe that attentional blink is caused by the brain balancing demands on its limited resources. As soon as the brain processes the first target, it can focus attention on the second target, allowing us to become aware of it and remember it. But if the second target appears while the first target is still being processed, then the brain actively suppresses information about the second target to avoid it interfering with the first target.

Next steps:
The researchers would like to determine whether the attentional blink exists in mice. If it does, they will record the activity of cells in different regions of the mouse brain to study how these regions work together to control visual attention.

Tang, M. F., Ford, L., Arabzadeh, E., Enns, J. T., Visser, T. A. W., & Mattingley, J. B. (2020). Neural dynamics of the attentional blink revealed by encoding orientation selectivity during rapid visual presentation. Nature Communications, 11(1), 1–14. doi: 10.1038/s41467-019-14107-z

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