When you’re engrossed in a task, you’ll often fail to notice what’s going on around you. Researchers can take advantage of this phenomenon, known as ‘inattentional blindness’, to test what happens in the brain in response to attention and awareness. Figuring that out is critical to understanding consciousness.
One of the features of brain activity that has been linked to attention and awareness is alpha oscillations – brain waves that oscillate at a frequency of 8–12 Hz. However, it has been difficult to tell how alpha oscillations are linked to these two processes, as they are closely related in the brain.
To understand the link to awareness alone, Brain Function CoE researchers Anthony Harris, Paul Dux and Jason Mattingley, from the University of Queensland, tested participants on an inattentional blindness task. Two groups of participants viewed a computer screen that was split into three sections. They were asked to focus on the middle section, and to report when they saw a particular number of coloured shapes. During the test, the researchers measured the participants’ alpha oscillations using electroencephalography (EEG).
One group was told at the beginning of the test that the left and right sections of the screen would also display shapes, which they should ignore. They were expected to be aware of these peripheral shapes, but not pay attention to them. The other group were told the same thing, but only halfway through the test. That means that in the first half of the test, these participants were expected to neither be aware of, nor pay attention to, the peripheral shapes.
The researchers analysed the alpha oscillations when a shape was present (and subject to either awareness or inattentional blindness) or absent. They found that when participants were not aware of a shape, their alpha oscillations did not change relative to when the shape was absent. But whenever participants were aware of a shape, their alpha oscillations at 10 Hz were suppressed.
This finding suggests that alpha oscillations are directly linked to awareness.
The researchers plan to study how perception is affected by the position of the brain wave at the time a stimulus appears – for example, whether it is at a ‘peak’ or a ‘trough’. They will also investigate whether perception is linked to other attention-related behaviours, such as the timing of eye movements.
Harris, A.M., Dux, P.E., & Mattingley, J.B. (2020). Awareness is related to reduced post-stimulus alpha power: a no-report inattentional blindness study. European Journal of Neuroscience, 52, 4411-4422. doi: 10.1111/ejn.13947