Ever felt like you’re struggling to think about too many things at once? That might be because your brain’s attention systems are full.
A new brain-scanning method that shows how much energy nerve cells are using has provided more support for the idea that we only have a finite amount of attention available.
The findings also help explain the bizarre “invisible gorilla” optical illusion. In this, people watching a staged video can completely fail to see a man in a gorilla suit taking a leisurely stroll through a group of actors because they’re too busy concentrating on what the actors are doing.
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How we pay attention to only certain aspects of the torrents of information produced by our senses is one of the many mysteries of consciousness. Nilli Lavie at University College London has proposed that our brains only have a finite amount of attention, and that when that capacity is reached, we start ignoring other things.
Her group has previously found support for this idea by doing .
Although fMRI brain scans have become a mainstay of neuroscience research, they have drawbacks. They require people to lie inside a huge machine, and the scans can’t directly measure the activity of nerve cells; instead they provide an indirect measure by showing which parts of the brain are using the most oxygen and so are likely to be at work.
Hard-working cells
The new brain scanning method, called broadband functional near infra-red spectroscopy, was first developed as a way of measuring the brain’s oxygen levels with a simple headset, like an easier way to do fMRI.
But a research group at UCL has tweaked the machinery so that instead of oxygen, it measures the activity of an enzyme inside mitochondria, tiny structures that provide energy to cells. This provides a more direct measure of how hard brain cells are working. “We are measuring the metabolism inside the neuron,” says Lavie.
In her latest experiment, people did a visual task – either an easy or hard version – that involved spotting certain shapes and colours on a screen. Half the time they were also shown a flickering chequerboard pattern in the periphery of their vision.
When the main task was easy, the brain cells dealing with peripheral vision raised their firing rates when the pattern started flashing. When the main task was difficult, the flashing chequerboard pattern led to little increase in neural activity. “You suppress things you’re not attending to,” says Lavie, who presented the findings at a recent .
Jan de Fockert of Goldsmiths, University of London, who was not involved in the research, says other work has shown that demands on our attention from one sense can affect other senses too. “That’s why it can be dangerous to have a fun conversation while driving a car.”
