fMRI Measurements of Visual Attention
Functional magnetic resonance imaging (fMRI) is a novel, non-invasive method for measuring activity in the human brain, and for investigating the relationship between brain activity and behavior. The technique is similar to conventional MRI, which is used to acquire structural images of the brain, but fMRI can generate images of brain activity in addition to brain anatomy. It works again by measuring the flow of blood in the brain. The brain controls the flow of oxygenated blood to brain regsions where there is more neuronal activity. Oxy- and dexy-hemoglobin have different magnetic properties, and this can be picked up by the MR scanner.
The study of attention has a very long history within psychology, dating back more than 100 years. We now know that when people attend (without moving their eyes) to certain visual stimuli to perform a task, the responses of some visual neurons are enhanced compared to when attention is directed elsewhere.
Below is a demonstration of attention modulates brain activity in visual cortex. In the experiments, subjects fixated the center of a display while performing a visual discrimination task on either the right or the left half of the display. Stimuli on the right are processed by neurons in the left hemisphere and vice versa. The stimuli were always the same and the subjects did not move their eyes, only the instructions to attend to one side or the other varied.
Top: Illustration of the stimulus. The yellow circle was
not actually present in the experiments; it indicates where the subject
is instructed to attend.
Bottom: Axial (horizontal) slice through the of the brain with
functional activity superimposed in color. The superimposed colors
indicate regions of brain actiivty. Activity in the left hemisphere
increases when the subject attends to the right and vice versa.
Further information about this research.