Aug. 28, 2012 Like a melody that keeps playing in your head even after the music stops, researchers at the Beckman Institute have shown that the beat goes on when it comes to the human visual system.
In an experiment designed to test their theory about a brain mechanism involved in visual processing, the researchers used periodic visual stimuli and electroencephalogram (EEG) recordings and found, one, that they could precisely time the brain's natural oscillations to future repetitions of the event, and, two, that the effect occurred even after the prompting stimuli was discontinued. These rhythmic oscillations lead to a heightened visual awareness of the next event, meaning controlling them could lead to better visual processing when it matters most, such as in environments like air traffic control towers.
The research was reported by Beckman faculty members Monica Fabiani, Gabriele Gratton, Diane Beck, Alejandro Lleras, first author and Beckman Fellow Kyle Mathewson, and undergraduate psychology student Christopher Prudhomme. The paper was published online last week in the Journal of Cognitive Neuroscience.
The researchers wrote that this entrainment of brain oscillators can be used to lock the timing of repetitive brain activity and, therefore, enhance, "processing of subsequently predictable stimuli."
"In nature, rhythmicity is everywhere, so it makes sense that our brain has evolved to be sensitive to rhythms in the world and to be able to latch on to them to improve neural processing," Lleras said. "It's very nice to be able to show that not only does the brain work in this oscillatory fashion but that we can harness that property that is inherent to the brain and use it to control the brain's response."
This study follows their 2010 report involving a brain entrainment experiment in which a series of repetitive flashes were presented and followed by a faint target stimulus. They found that participants were only aware of those targets whose timing could be predicted based on the rhythm of the previous flashes; targets presented on the off-beat were not seen. The authors wrote that "awareness of near-threshold stimuli can be manipulated by entrainment to rhythmic events, supporting the functional role of induced oscillations in underlying cortical excitability, and suggest a plausible mechanism of temporal attention."
Gratton said their idea in this most recent experiment was "to manipulate the brain activity and see if this manipulation was in fact predictive of performance for this phenomenon."
It was. Using EEG to test their theory, they were able to assess the brain's predictive responses, as well as show they could control them.
"We hooked up EEGs to measure the electrical activity from people's brains to see if their brain waves were becoming locked to the rhythms, and they were," Mathewson said. "Then we showed that their visibility of the target fluctuated depending on the timing with respect to this rhythm. So we locked in the timing of their brainwaves and that locked in their ability to see the world at a certain time."
The research line goes back to a discovery by Mathewson of a pulsed inhibition mechanism in the brain that is based on oscillations in the alpha phase. This discovery supported the theory that the brain sometimes samples the visual environment in rhythmic "frames" rather than continuously, as the term "brain waves" implies.
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The above story is based on materials provided by Beckman Institute for Advanced Science and Technology. The original article was written by Steve McGaughey.
- Kyle E. Mathewson, Christopher Prudhomme, Monica Fabiani, Diane M. Beck, Alejandro Lleras, Gabriele Gratton. Making Waves in the Stream of Consciousness: Entraining Oscillations in EEG Alpha and Fluctuations in Visual Awareness with Rhythmic Visual Stimulation. Journal of Cognitive Neuroscience, 2012; : 1 DOI: 10.1162/jocn_a_00288
Note: If no author is given, the source is cited instead.