Aging and Attentional Guidance During Visual Search

1
Aging and Attentional Guidance During Visual
Search Functional Neuroanatomy by PET David J.
Madden1,2, Timothy Turkington3, James M.
Provenzale3, Laura L. Denny1, Thomas C. Hawk3,
and R. Edward Coleman3 1Center for the Study of
Aging and Human Development, 2Department of
Psychiatry and Behavioral Sciences and
3Department of Radiology, Duke University
Medical Center, Durham, NC 27710
RESULTS
INTRODUCTION
2


4
Visual Search Accuracy
Correlation of rCBF Activation with Search
Accuracy
In a positron emission tomography (PET) study of
visual search Madden et al. (1997) reported that,
relative to a selective attention condition,
divided attention was associated with both an
age-related decline in the activation of neural
regions mediating visual processing
(occipitotemporal cortex) and an increase,
perhaps as a compensatory mechanism, in the
activation of prefrontal cortex. In the Madden et
al. study, the spatial location of the search
target was constant (in the center of the
display) in the selective attention condition and
varied unpredictably in the divided attention
condition. Participants could thus guide
attention to the target on the basis of a
predefined and constant spatial location. In the
present experiment we investigated whether age
differences in cortical activation would be
evident when the opportunity to guide attention
was independent of the spatial location of the
target.
v Across all three task conditions, the
covariation of rCBF activation with search
accuracy (1 corrected recognition) was more
pronounced for younger adults than for older
adults.

• For both age groups, there was a decline in
  search accuracy (hits minus false alarms) as
  perceptual similarity among display items
  increased, but this decline was more pronounced
  for older adults than for younger adults.
• Both age groups were successful in using color to
  guide attention to the target item, as indicated
  by the improvement in search accuracy in the
  Guided condition, relative to the Conjunction
  condition.

5
Normalized rCBF
Younger Older   Adults Adults M SD
M SD Conjunction minus Feature   Right
fusiform gyrus (BA 19) Conjunction 1.093 0.053 1
.122 0.047 Feature 1.074 0.052 1.124 0.045   Ri
ght striate cortex (BA 17) Conjunction 0.948 0.0
55 1.027 0.050 Feature 0.930 0.054 1.024 0.043
  Conjunction minus Guided  Right striate cortex
(BA 17) Conjunction 0.968 0.056 1.036 0.049   Gu
ided 0.952 0.053 1.042 0.054   Right fusiform
gyrus (BA 19) Conjunction 1.055 0.055 1.104 0.05
2   Guided 1.039 0.048 1.108 0.055   Left
fusiform gyrus (BA 19) Conjunction 1.115 0.049 1
.187 0.066   Guided 1.084 0.039 1.181 0.071  
METHOD

• Participants
• 12 younger adults (mean age 23 yrs, range 20-27
  yrs) and 12 older adults (mean age 66 yrs, range
  60-77 yrs). Participants were right handed and
  neurologically normal as determined by MR
  screening.
• Stimuli and Procedure
• On each trial, participants made a yes/no
  decision regarding the presence of a single
  upright L (the target) among rotated Ls
  (distractors). Each display contained 18 items.
  Location of the target was distributed across 25
  display positions (see Figure 1).
• There were three conditions that varied the
  difficulty of the search task, by varying the
  similarity of the target and distractor items.
  Feature the target was always the single item of
  a different color. Conjunction each display
  contained 9 black items and 9 white items,
  distributed randomly. Guided each display
  contained three items, distributed randomly,
  sharing the targets color. Because the
  probability that a target was present in a
  display was .50, the incidence probability of
  target-relevant items (those sharing the color of
  the target) was .028 in the Feature condition,
  .167 in the Guided condition, and .50 in the
  Conjunction condition.
• Each trial began with a central fixation point
  for 500 ms, followed by a display for 1 s. The
  offset of the display was followed by a blank
  interval that varied randomly from 800 ms to
  1,200 ms. There were 100 displays (50
  target-present, 50 target-absent) in each trial
  block.
• PET Scanning
• Measurement of regional cerebral blood flow
  (rCBF) was conducted with a GE Advance whole-body
  PET scanner (35 imaging planes separated by 4.25
  mm). Intrinsic in-plane and axial spatial
  resolutions were approximately 5 mm.
• Radiotracer administration was intravenous bolus
  injection of 10 mCi of H215O. Data acquisition
  was performed in the 3D mode (septa out). Each
  search condition was performed during a separate
  PET scan. There was a total of 12 emission scans,
  four scans for each of the three search
  conditions.

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rCBF Activation

• Voxels were thresholded for height at Z 2.33 (p
  lt .01, uncorrected). The rCBF activation was
  estimated from subtraction images based on linear
  contrasts (SPM96), using global activity and
  volume of cortical gray matter as covariates.
  Significant differences in rCBF (p lt .05,
  corrected) are overlaid on the composite MR image
  of the participants in each age group.

Younger Adults
Older Adults
Conjunction minus Feature
Conjunction minus Feature
-20
12
-20
12
20
52
52
20
Conjunction minus Guided
Conjunction minus Guided

• Analyses were conducted of the PET counts for the
  SPM local maxima, normalized to the counts of the
  mean gray matter in each task condition.
• For each local maximum, the task condition effect
  was significant for younger adults but not for
  older adults.
• Age differences in rCBF occur not as a result of
  relatively higher rCBF for younger adults in more
  difficult task conditions, but rather as a result
  of relatively lower rCBF for younger adults in
  easier task conditions.

2.33 5.29
-20
12
-20
12
Z Value
2.33 3.97
20
52
52
20
Guided minus Feature
Guided minus Feature
-20
12
-20
12
52
20
52
20

• Activation within each age group (blue color
  scale) was significant for the Conjunction
  condition, relative to the Feature condition,
  throughout occipital, parietal, and prefrontal
  regions.
• Activation differed significantly between age
  groups (red color scale) primarily in the
  occipital cortex of the right hemisphere, with
  the activation being greater in magnitude for
  younger adults than for older adults.
• For younger adults, activation in the Guided
  condition was similar to that in the Feature
  condition. For older adults, in contrast,
  activation in the Guided condition resembled that
  in the Conjunction condition.

References
Madden, D.J., Turkington, T.G., Provenzale, J.M.,
Hawk, T.C., Hoffman, J. M., Coleman, R.E.
(1997). Selective and divided visual attention
Regional cerebral blood flow measured by H215O
PET. Human Brain Mapping, 5, 389-409
Acknowledgements
This work was supported by National Institute on
Aging grant R01 AG11622.
1
Experimental Design/Sample Displays for Each Task
Condition
CONCLUSIONS

• Although both age groups are able to use a
  spatially distributed property of the display,
  color, to guide search, older adults maintain
  relatively higher levels of rCBF across task
  conditions. Age differences in occipital
  activation represent younger adults lower levels
  of rCBF when the opportunity for attentional
  guidance is available.

• Target detectability during conjunction search is
  lower for older adults than for younger adults.
• Age-related changes in rCBF in this task reflect
  activation of occipital cortex rather than
  recruitment of prefrontal cortex.