Age-related differences in frontoparietal activation for target and distractor singletons during visual search

Abstract

Age-related decline in visual search performance has been associated with different patterns of activation in frontoparietal regions using functional magnetic resonance imaging (fMRI), but whether these age-related effects represent specific influences of target and distractor processing is unclear. Therefore, we acquired event-related fMRI data from 68 healthy, communitydwelling adults ages 18-78 years, during both conjunction (T/F target among rotated Ts and Fs) and feature (T/F target among Os) search. Some displays contained a color singleton that could correspond to either the target or a distractor. A diffusion decision analysis indicated age-related increases in sensorimotor response time across all task conditions, but an age-related decrease in the rate of evidence accumulation (drift rate) was specific to conjunction search. Moreover, the color singleton facilitated search performance when occurring as a target and disrupted performance when occurring as a distractor, but only during conjunction search, and these effects were independent of age. The fMRI data indicated that decreased search efficiency for conjunction relative to feature search was evident as widespread frontoparietal activation.Activation within the left insula mediated the age-related decrease in drift rate for conjunction search, whereas this relation in the FEF and parietal cortex was significant only for individuals younger than 30 or 44 years, respectively. Finally, distractor singletons were associated with significant parietal activation, whereas target singletons were associated with significant frontoparietal deactivation, and this latter effect increased with adult age. Age-related differences in frontoparietal activation therefore reflect both the overall efficiency of search and the enhancement from salient targets.

Neural correlates underlying local and global processing during visual search across adulthood

“…Critically, the activation of the insula was not observed in older participants during the local processing, suggesting a salience network impairment with healthy aging. This finding is contrasting with the study by Merenstein et al [ 29 ] as the authors described age-related increases in activation in the insula during a visual search task (conjunction (T/F target letters among rotated Ts and Fs) > feature (T/F target letters among Os) contrast). Their diffusion decision analyses further suggested a significant mediation role of the insula activation in predicting an age-related decrease in the rate of evidence accumulation during the conjunction search.…”

“…Importantly, in such a context, a bottom-up selection—indicated by the selection being determined by the feature properties present in the environment, regardless of top-down control [ 45 ]—is involved. However, as soon as the environment becomes more visually complex and involves top-down processing to select the correct target (i.e., local processing in presence of visual distractors), brain and behavioral differences appear with late adulthood (see also [ 29 ]), as discussed further below.…”

“…In contrast, global processing has been rather associated with the activation of the central-executive network [ 26 ]. However, it should be noted that both networks have also been typically detected as activated during more traditional visual search fMRI tasks that did not involve any local or global level of detection [ 29 , 38 , 39 ]. In this context, these networks have been suggested to support all stages of visual search with each network supporting more specific mechanisms.…”

“…Overall, these findings have been more largely investigated in early adulthood and it is unclear which underlying neural network may be more impacted by aging during visual search tasks and lead to behavioral differences between early and late adulthood as described above. An fMRI study [ 29 ] conducted on healthy adults aged 18–78 years suggested age-related differences in activation in the fronto-parietal network during a visual search task, which they linked to overall efficiency of search and the saliency of the visual targets. While this task involved different types of distractors, it did not involve any local or global targets.…”

Age-related fornix decline predicts conservative response strategy-based slowing in perceptual decision-making

“…Magnetic resonance imaging (MRI) studies have found age-related increases in boundary separation to be associated with reduced striatal activity [as measured with the blood oxygen level dependent (BOLD) signal] [39] and with reduction in fractional anisotropy (a diffusion tensor imaging (DTI) based measurement of fiber directionality/coherence) in white matter connections between the striatum and the pre-Supplementary Motor Area (preSMA) [26] . Other studies have linked age-related increases in non-decision time [47] , [48] and in drift rate [51] to differences in the BOLD signal in fronto-parietal regions. These findings are consistent with evidence suggesting that reductions in fronto-parietal activity may underpin age-related slowing in simple and choice RT tasks and SAT [8] , [36] , [45] , [56] .…”