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Younger Older  AdultsAdults MSDMSD Conjunction minus Feature PowerPoint PPT Presentation


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1.0. Older Adults. Younger Adults. -20. +20. -20. +20. .90. .80. Corrected Recognition. .70. .60. Young. +28. +68. +28. +68. .50. Older. Z Value. Z Value. .40. 2.33 5.65. 2.33 4.21. 2.33 5.49. .028. .167. .50. Feature. Guided. Conjunction. Similarity.

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Younger Older  AdultsAdults MSDMSD Conjunction minus Feature

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Younger older adults adults m sd m sd conjunction minus feature

1.0

Older Adults

Younger Adults

-20

+20

-20

+20

.90

.80

Corrected Recognition

.70

.60

Young

+28

+68

+28

+68

.50

Older

Z Value

Z Value

.40

2.33 5.65

2.33 4.21

2.33 5.49

.028

.167

.50

Feature

Guided

Conjunction

Similarity

2.33 7.17

2.33 7.18

Z Value

Z Value

2.33 3.84

2.33 4.65

Z Value

2.33 5.01

2.33 5.46

Z Value

Z Value

Guided

Conjunction

Feature

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

Correlation of rCBF Activation with Search Accuracy

Visual 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.

vAcross 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  AdultsAdults

MSDMSD

Conjunction minus Feature

Right fusiform gyrus (BA 19)

Conjunction1.0930.0531.1220.047

Feature1.0740.0521.1240.045

Right striate cortex (BA 17)

Conjunction0.9480.0551.0270.050

Feature0.9300.0541.0240.043

Conjunction minus Guided

Right striate cortex (BA 17)

Conjunction0.9680.0561.0360.049

 Guided0.9520.0531.0420.054

Right fusiform gyrus (BA 19)

Conjunction1.0550.0551.1040.052

 Guided1.0390.0481.1080.055

Left fusiform gyrus (BA 19)

Conjunction1.1150.0491.1870.066

 Guided1.0840.0391.1810.071

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 target’s 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.

3

rCBF Activation

  • Voxels were thresholded for height at Z = 2.33 (p < .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 < .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

+20

+52

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

+12

-20

Z Value

2.33 3.97

+20

+52

+20

+52

Guided minus Feature

Guided minus Feature

+12

-20

-20

+12

+52

+20

+20

+52

  • 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.


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