Our sensory system is constantly bombarded with inputs, but owing to the brain’s finite
processing power, we are forced to pay attention to only a tiny proportion of these
inputs at any given time. In a new study, Richard Davidson and colleagues report that
intensive training in meditation can alter the way in which the brain allocates attentional
resources to important stimuli, allowing people to improve their performance on a
demanding visual task.
In the “attentional blink” task, volunteers were asked to identify two “target” stimuli—for
example, two particular numbers—in a stream of rapidly presented “non-target” stimuli—for
example, letters—which are irrelevant to the task. When the first target number appears
on the screen, it captures the attention of the subject, and this can prevent the
person from spotting the second target if it appears within around half a second of
the first (the attentional blink). It is as if the brain is so busy processing the
first target that it can’t also process the second, and therefore the second target
goes unnoticed. However, the attentional blink does not represent a structural processing
bottleneck. Most subjects are able to spot the second target on at least a small proportion
of trials. Since this task gauges the ability of subjects to allocate cognitive resources
efficiently when multiple stimuli compete for attention, it is perfectly suited for
investigations of the effects of mental training on attention.
Previous studies had reported that the act of meditation can alter cognitive and perceptual
abilities and neural responses. However, Davidson and colleagues wondered whether
volunteers who received three months of intensive training in a particular type of
meditation, known as Vipassana meditation, would allocate attentional resources more
efficiently and therefore show enhanced performance on the attentional blink task,
a task that taps into similar skills used during training without directly involving
meditation. Vipassana meditation encourages “non-reactive awareness”—a state of mind
in which individuals cultivate awareness of stimuli without judgments or affective
responses to those stimuli.
Since Vipassana meditation allegedly reduces mental distraction, the authors hypothesized
that volunteers (“practitioners”) who attended the intensive training course, which
involved 10–12 hours of meditation each day, would be more successful at identifying
the second target, because the subjects’ attention would be captured less by the first
target. Performance on the task before training was compared with performance after
training, and also with that of a control group (“novices”) who were interested in
meditation but received only one hour of training, and meditated for 20 minutes each
day for the week that preceded each experimental session.
After the three-month training period, each member of the practitioner group showed
improved detection of the second target, if it appeared within half a second after
the first target. Only 16 out of 23 of the novice group showed a similar improvement.
This reduction in the effect of the attentional blink is consistent with the idea
that after training, practitioners were allocating a smaller proportion of their brains’
resources to the first target.
Another way of measuring the allocation of attention is to use event-related potentials—electrical
changes associated with neural responses to sensory stimuli or cognitive tasks, which
can be recorded through the scalp. When event-related potentials are recorded from
subjects during the attentional blink task, a noticeable electrical change—called
the P3b—is associated with the appearance of the first target. This event is believed
to reflect the allocation of resources to the target. In the practitioner group, after
three months of intensive mental training, the P3b that was associated with the first
target was significantly smaller for those trials in which the subject was able to
identify both targets. In other words, the event-related potentials appeared to show
that less attention was being allocated to the first target, and this allowed the
subjects to spot the second target.
To investigate further the possible link between attentional resource allocation,
as reflected by the size of the P3b potential, and performance on the attentional
blink task, the authors compared individual performance on the task with the event-related
potentials recorded from each subject. Subjects who showed the largest decrease over
time in the size of the P3b evoked by the first target also generally showed the greatest
improvement in detection of the second target. This result further corroborates the
view that the attentional blink is caused by excessive allocation of attentional resources
to the processing of target 1.
Importantly, the subjects did not meditate during the attentional blink task. So these
results indicate that intensive mental training can produce lasting and significant
improvements in the efficient distribution of attentional resources among competing
stimuli, even when individuals are not actively using the techniques they have learned.