Brain gain
Attention enhances initial brain responses to sights and sounds
Each moment that we are awake, our senses are bombarded with stimuli. Focusing our attention on the few stimuli that are important allows us to filter out the ones irrelevant to the task at hand.
The first parts of the brain to respond to objects and sounds in the environment are the so-called ‘primary’ visual and auditory cortex, respectively. Paying attention to sounds in one ear enhances the initial response of the primary auditory cortex on the opposite side. But previous studies have not found the same to be true in the primary visual cortex in subjects paying attention to objects in the visual field.
Now, Vahe Poghosyan and Andreas A. Ioannides at the RIKEN Brain Science Institute in Wako have found that attention does in fact modulate primary cortical responses to both auditory and visual stimuli (1).
The researchers directed five human subjects to pay attention to a pre-determined sound coming into one ear, or to a pre-determined image within a specific part of the visual field. They then presented a variety of auditory and visual stimuli, and asked the subjects to respond only to the pre-determined sound or image by raising their finger, ignoring all of the irrelevant stimuli. For example, a subject may be told to respond only to sound in the right ear, and to ignore sound in the left ear, as well as any presented images.
During these experiments, the researchers recorded the activity of different areas of the subjects’ brains using magnetoencephalography (MEG), which measures magnetic fields produced by electrical activity of large populations of neurons (Fig. 1). Then, using analytical methods not used in earlier studies, they found that attention focused on pre-determined stimuli increased the activity in both the primary visual and auditory cortex almost as soon as the stimuli arrived there.
Ioannides believes that previous studies did not come to a similar conclusion about the role of attention on the primary visual cortex because these studies attributed the early MEG signals “to the primary visual cortex only, ignoring other fast activity in areas beyond the primary visual cortex. This introduced a small error in the location of the primary visual cortex, enough to ‘wash away’ the early attention effect on the primary visual cortex,” he says.
The findings suggest that attention to a location in the visual field modulates the earliest sensory processing in the brain of stimuli appearing there.
Reference
1. Poghosyan, V. & Ioannides, A.A. Attention modulates earliest responses in the primary auditory and visual cortices. Neuron 58, 802–813 (2008).
