THE ROLE OF ATTENTION IN COGNITIVE DISABILITIES
Marie T. Banich
Dept. of Psychology, University of Colorado at Boulder
Dept. of Psychiatry, University of Colorado Health Sciences Center
Neutral
Introduction
What is attention?
The focus of our laboratory is to utilize modern brain-imaging
techniques to understand the neural systems that control attention.
Although there is no single generally agreed upon definition of
attention, all models invoke the idea of selection. Since the brain
receives and must process much more information than it can
handle at one time, there must be a way to select the information
that is critical for task performance. This selection can occur at
multiple stages of processing - with regards to incoming sensory
information, with regards to information that must be “kept in
mind”, and with regards to the possible responses. The ability to
control attention is a basic process that must occur for any mental
function to occur successfully. For example, recognizing an
object requires selecting the relevant visual features while
disregarding others, remembering a story requires selecting the
critical themes and disregarding extraneous details, and so forth.
The role of attention in cognitive disability
Given its central role in most mental functions, it is not
surprising that attentional problems are commonly observed in
learning disabilities and occur as a consequence of brain injury.
The importance of attentional function for cognitive disabilities is
broad-ranging. In addition to being the cardinal symptom of
attention deficit disorder, attentional problems occur in various
types of dementia (e.g., Morris, 1996) including the early stages
of Alzheimer’s disease (e.g., Baddeley, Baddeley, Bucks, &
Wilcock, 2001), and are a common consequence of stroke,
predicting the degree of subsequent recovery (e.g., Paolucci et al,
2001).
Attentional problems are also one of the major
consequences of head injury (Cossa & Fabiani, 1999), lingering
even in the case of mild head injury (e.g., Potter, Bassett, Jory &
Barrett, 2001). Rehabilitation programs for brain injury involve
addressing attentional difficulties (Cicerone et al, 2000), which
have been posited to be a key roadblock to independent
functioning and reintegration into the community (e.g., Chan,
2001) .
How is attention controlled by the brain?
Given that attention is affected in a large variety of
cognitive disabilities, it is not surprising that it is controlled by a
network of brain structures. Hence, damage to any component
can degrade performance. The brain regions typically implicated
in attentional control include regions of the prefrontal cortex, the
anterior cingulate, parietal regions, and sensory regions that
process task-related information. These regions are shown below.
Incongruent
DOOR
Neutral
Incongruent
BLUE
HOUSE
Identify each word’s ink color
(yellow, green, blue) using a
3-button response pad.
ABOVE
Identify the word’s location
(above, below or inside the box)
using a 3-button response pad.
Identify the ink color:
Response conflict
Incongruent>Neutral
Color-word
Spatial-word
Dorsolateral cortex
becomes active
regardless of what type
of information is taskrelevant
Inferior
prefrontal
cortex
In another study, we found that dorsolateral prefrontal cortex is only
active when it is hard to impose an attentional set (Banich et al,
2000b). In this study we compared performance on a color-word
and color-object task. Once again we compared incongruent to
neutral trials. In this study, we either had individuals pay attention
to the color or the item (the word or the object). In the color-word
task, it is easy to pay attention to the word, since we read relatively
automatically, as compared to the color. However, the relationship is
opposite in the color-object task, it is easier to pay attention to the
color than the object.
Color-Word Stimuli
N eu tra l
Color-Object Stimuli
In co n gr ue nt
DOOR
N eutra l
In co ngr ue nt
B L UE
How do we examine attention?
To examine attentional control, we utilize variants of a
simple but powerful task that has been referred to as the “gold
standard” of attentional control, the Stroop task. In this task,
individuals must pay attention to one element of the stimulus, the
task-relevant dimension (e.g. color), while ignoring another
dimension of the stimulus, the task-irrelevant dimension (e.g.,
shape). To examine brain activity during performance of these
tasks, we use functional magnetic resonance imaging (in
collaboration with the Depts. of Radiology and Psychiatry at
University of Colorado Health Sciences Center).
=
Incongruent Ineligible
LOT
Neutral
The anterior cingulate
showed the expected pattern
- responding when the word
names a conflicting
response, but not when it
does not.
C. The temporal relationship between brain regions as one learns
to impose atentional control.
In this study we wanted to see the timing relationships of brain regions
that become active as one learns to impose attentional control (Milham
et al, submitted). To do so we taught people to 100% accuracy to learn
to associate a color name with a nonsense shape.
“green”
“blue”
After training, we examined their response to either incongruent or
neutral trials.
Attend to color-EASY
Attend to item (word)-EASY
Attend to item (object)-HARD
Incongruent>Neutral
Color-Word Attend to:
Color-Object
Color
Easy
Hard
Item
B. Selecting a correct response: Role of the anterior
cingulate
We have performed a number of studies that indicate that the
anterior cingulate, in particular the posterior dorsal segment, is
responsible for selecting the response that an individual makes.
First, the cingulate is active when the word in the color-word Stroop
task names a conflicting response, but not when the word names a
congruent response or has no response value (i.e., is neutral).
Response conflict
Our Prior Findings
A. Creating an attentional “set”: The role of the dorsolateral
prefrontal cortex
Incongruent
Incongruent > Congruent
No response conflict
>
We examined performance over a series of trials, dividing the session
into thirds. Below is shown how well activity for cingulate and
associated regions (above) and dorsolateral regions (below) is
associated with greater activity on incongruent than neutral trials.
1st third
2nd third
=
HOUSE
Neutral
ORANGE
Congruent
Incongruent > Neutral
Congruent >Neutral
R
L
Last third
The activity of four
different medial frontal
regions decreases with
training, indicating that
it becomes easier to
reduce response
conflict with practice.
Hard
Dorsolateral prefrontal cortex becomes active when it is important to
impose an attentional set, but is not activated when a process can be
done relatively automatically.
GREEN
We have found that the dorsolateral prefrontal cortex is critical
for the ability to create an attentional set - that is the ability to
keep in mind what is task-relevant while ignoring that which is
task-irrelevant. Such an attentional set is necessary when taskirrelevant information is distracting. A number of our studies
support this assertion. First, we found that this region becomes
active whenever it is hard to pay attention, regardless of what you
need to pay attention to - an item’s color, its spatial relationship,
and so forth. In one study, we compared variants of the Stroop
task, a color-word task and a spatial-word Stroop task (Banich et
al., 2000a). We vary attentional demands so that in the more
demanding condition, the distracting information, the word,
conflicts with the task-relevant information (e.g,. color or spatial
relationship), while in the easier condition, it is does not.
Incongruent Eligible
RED
“yellow”
Attend to color-HARD
Easy
One of the major issues of scientific debate in the field currently
is exactly what roles each of these regions play in attentional
control. In our laboratory, we have focused on disentangling the
roles of these different regions, so that we can understand the
precise way in which the brain controls attention.
>
BLUE
Eligible > Ineligible = Neutral
Posterior sensory cortex
Anterior cingulate
cortex
No response conflict
Both
Parietal cortex
Dorsolateral
prefrontal
cortex
To examine this issue further, we performed another study (Milham et
al, in press b). We reasoned that if this area is specific to response
selection, it should only be active when the word provides conflicting
information about a response, but should be impervious to conflict at
other levels, such as meaning. Furthermore, it should exhibit no
difference in activity between neutral words and incongruent color
words that don’t name a possible response (called incongruent response
ineligible trials).
The activity of three
different dorsolateral
regions stays constant
since an attentional set
must be retained
regardless of practice.
Implications for Cognitive
Disabilities
Knowledge about how the brain regulates attentional control has
important implications for: 1) understanding the nature of cognitive
disabilities themselves, 2) for evaulating the efficacy of treatment
programs and for 3) the design of devices that can improve the lives of
individuals with attentional dysfunction. For example, our findings
indicate that the design of an attentional aid should have two important
attributes: a means to help the disabled person remain focused on
information that is critical to performance of the task, and a means of
helping them decide among the array of possible responses.
Furthermore, our results suggest that as an individual becomes wellacquainted with a task, it might be possible to employ a more
“streamlined” device that places less emphasis on the selection of
responses.
References
Response conflict vs.
none
Response conflict vs.
none
Cingulate activity when there is
response conflict
None vs. none
No cingulate activity when
there is no response
conflict
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