Exploring interhemispheric collaboration in older compared to younger adults

Physical and Name Identity letter-matching tasks were used to explore differences in interhemispheric collaboration in younger and older adults. To determine whether other factors might also be related to across/within-hemisphere processing or visual field asymmetries, neuropsychological tests measuring frontal/executive functioning were administered, and comparisons were made for participants split into low and high efficiency groups based on performance on the letter-matching tasks. A Task by Across/Within interaction was found for both groups, but with a stronger within-hemisphere advantage for the Physical Task and a weaker across-hemisphere advantage for the Name Task for older participants. More efficient groups and better performers on several neuropsychological tasks showed a reduced across-hemisphere advantage for the Name Identity task. Findings suggest that computational complexity, specific task demands, and perhaps trade-offs between age-related changes in gray and white matter all contribute to whether processing loads are distributed across or within hemispheres as we age.     

Neural Recruitment and CognitiveAging: Two Hemispheres Are Better Than One, Especially as You Age

Several neuroimaging studies have reported that older adults show weaker activations in some brain areas together with stronger activations in other areas, compared with younger adults performing the same task. This pattern may reflect neural recruitment that compensates for age-related neural declines. The recruitment hypothesis was tested in a visual laterality study that investigated age differences in the efficiency of bihemispheric processing. Letter-matching tasks of varying complexity were performed under two conditions: (a) matching letters projected to the same visual field (hemisphere) and (b) matching letters projected to opposite visual fields (hemispheres). As predicted by the recruitment hypothesis, older adults generally performed better in the bilateral than unilateral condition, whereas younger adults showed this pattern onlyfor the most complex task. We discuss the relation between these results and neuroimaging evidence for recruitment, and the relevance of the present bihemispheric advantage to other evidence for age-related changes in interhemispheric transfer.     

The impacts of task relevance and cognitive load on adults’ decision information search

ABSTRACT

Higher relevance may increase older adults’ engagement in cognitively demanding activities; however, whether this effect will maintain when available cognitive resources are limited? Consequently, we investigated the joint impact of task relevance and cognitive load on older and younger adults’ decision search behaviors. We adopted a 2 (age: young/old) × 2 (cognitive load: without load/with load) × 2 (task relevance: high/low) mixed design. Sixty-one younger and 63 older adults completed high-relevance and low-relevance decisions. Our results revealed that older (vs. younger) adults took more time and more alternative-based search before decision-making. Both age groups sampled less information with an additional memory task. Additionally, they spent more time and effort to sample more information on high-relevance (vs. low-relevance) decisions; however, such differences disappeared when with an additional memory task. Task relevance promoted both age groups' search engagement, but this effect was subjected to their available cognitive resources.     

Imagery Interference Diminishes in Older Adults: Age-Related Differences in the Magnitude of the Perky Effect

Studies have documented the negative effects of mental imagery on perception (also known as the Perky effect) in younger adults, but imagery-interference effects in older adults have never been assessed. Two experiments examined this issue directly. Experiment 1 demonstrated that visual mental images diminish visual acuity in younger adults (mean age = 19.0) but not older adults (mean age = 73.6). Experiment 2 obtained parallel results, showing that visual imagery interfered with performance on a visual detection task in younger (mean age = 18.7) but not older adults (mean age = 66.7). Processes underlying age-related differences in imagery-interference effects are discussed and implications of these results for changes in cognitive performance in older adults are considered.     

Aging and Individual Variation in Interhemispheric Collaboration and Hemispheric Asymmetry

ABSTRACT

Thirty younger (Mean Age = 19.9 years) and 20 older adults (Mean Age = 74.7 years) performed Physical and Name Identity letter-matching tasks (matches were either within or between hemispheres) to study age-related changes in 1) the efficiency with which the two hemispheres interact with each other and 2) hemispheric asymmetry. In order to determine whether age-related effects were associated with differences in cognitive resources, the same individuals completed a set of memory span tasks. Performance on the letter-matching tasks indicated that the costs of interhemispheric collaboration were greater for older than for younger participants. However, within the older group, the advantage of spreading processing across both hemispheres increased as memory span decreased, suggesting that older individuals who are challenged by cognitive complexity are more likely to show increased benefits from between-hemisphere processing than individuals who are not so challenged. There was also an overall left visual field/right hemisphere advantage for the younger but not for the older group, suggesting greater age-related declines in right- than left-hemisphere function.     

Validating age-related functional imaging changes in verbal working memory with acute stroke

Functional imaging studies consistently find that older adults recruit bilateral brain regions in cognitive tasks that are strongly lateralized in younger adults, a characterization known as the Hemispheric Asymmetry Reduction in Older Adults model. While functional imaging displays what brain areas are active during tasks, it cannot demonstrate what brain regions are necessary for task performance. We used behavioral data from acute stroke patients to test the hypothesis that older adults need both hemispheres for a verbal working memory task that is predominantly left-lateralized in younger adults. Right-handed younger (age ? 50, n = 7) and older adults (age > 50, n =21) with acute unilateral stroke, as well as younger (n =6) and older (n =13) transient ischemic attack (TIA) patients, performed a self-paced verbal item-recognition task. Older patients with stroke to either hemisphere had a higher frequency of deficits in the verbal working memory task compared to older TIA patients. Additionally, the deficits in older stroke patients were mainly in retrieval time while the deficits in younger stroke patients were mainly in accuracy. These data suggest that bihemispheric activity is necessary for older adults to successfully perform a verbal working memory task.     

The effect of age on rule-based category learning

An explicit, rule-based, category-learning task with abstract visual stimuli was administered to 50 healthy older adults and 48 younger adults. Accuracy and reaction time (RT) were examined for the effects of age, perceptual abilities, rule memory, rule complexity, stimulus novelty, and response competition. Older adults performed at equivalent levels to younger adults when applying a simple rule, but showed performance decrements when applying a more complex rule. The age effect interacted with both stimulus novelty and response competition, and was not eliminated after controlling for basic perceptual abilities and rule memory. The authors suggest that older adults show category learning deficits in conditions that require enhanced cognitive control. These results are discussed in reference to the growing body of literature regarding age-related change in executive abilities and frontal lobe function.     

The Effect of Age on Rule-Based Category Learning

ABSTRACT

An explicit, rule-based, category-learning task with abstract visual stimuli was administered to 50 healthy older adults and 48 younger adults. Accuracy and reaction time (RT) were examined for the effects of age, perceptual abilities, rule memory, rule complexity, stimulus novelty, and response competition. Older adults performed at equivalent levels to younger adults when applying a simple rule, but showed performance decrements when applying a more complex rule. The age effect interacted with both stimulus novelty and response competition, and was not eliminated after controlling for basic perceptual abilities and rule memory. The authors suggest that older adults show category learning deficits in conditions that require enhanced cognitive control. These results are discussed in reference to the growing body of literature regarding age-related change in executive abilities and frontal lobe function.     

Influence of mild cognitive impairment on visual word recognition

The present study examined the effects of normal aging and mild cognitive impairment (MCI) on visual word recognition. Madden et al. (1999) reported evidence of general slowing of cognitive processes in Alzheimer's disease (AD) patients relative to younger adults and healthy older adults using a lexical decision task. It was of interest to determine whether similar effects would be observed in MCI patients relative to healthy younger and older adults. We extended the lexical decision task paradigm developed by Allen et al. (2004b) on younger adults to an examination of the effect(s) of MCI on visual word recognition. Results from the present study showed that healthy older adults and MCI patients performed similarly. That is, both groups took longer than younger adults to process words presented in mixed-case than in consistent-case letters. Mild cognitive impairment patients, however, responded significantly more slowly than healthy older adults across all lexical decision task conditions and showed a trend toward larger case-mixing effects than healthy older adults, which suggests that MCI may result in poorer analytic processing ability. Based on the current findings, evidence of a generalized slowing of cognitive processes using a standard lexical decision task can be expanded to include not only AD patients, but also the preclinical stages of the disease as well.     

Visual word recognition without central attention: evidence for greater automaticity with advancing age

The present experiments examined the automaticity of word recognition. The authors examined whether people can recognize words while central attention is devoted to another task and how this ability changes across the life span. In Experiment 1, a lexical decision Task 2 was combined with either an auditory or a visual Task 1. Regardless of the Task 1 modality, Task 2 word recognition proceeded in parallel with Task 1 central operations for older adults but not for younger adults. This is a rare example of improved cognitive processing with advancing age. When Task 2 was nonlexical (Experiment 2), however, there was no evidence for greater parallel processing for older adults. Thus, the processing advantage appears to be restricted to lexical processes. The authors conclude that greater cumulative experience with lexical processing leads to greater automaticity, allowing older adults to more efficiently perform this stage in parallel with another task.     

Developmental differences in the allocation of processing capacity

Recently psychologists have formulated a comprehensive view of attention involving allocation of processing capacity. Although developmental changes in processing capacity have been proposed as one source of age differences in certain cognitive skills, there has been little systematic investigation of this hypothesis. In the present study, second and sixth graders and adults (8, 12, and 20 years of age, respectively) performed a letter-matching task (primary task) concurrently with an auditory detection task (secondary task). Changes in reaction time in the secondary task as a function of manipulations of the primary task were used to estimate capacity allocation to the primary task. Primary task variables included stage of processing (alerting, encoding, rehearsing, responding) and matching condition (physical-identity vs name-identity matching). Age differences in secondary task performance were found to be related to stage of processing but not to matching condition. Earlier stages of the letter match task (alerting, encoding) required somewhat more capacity allocation in younger subjects. Later stages (rehearsing, responding) made substantially higher demands on capacity in children. Capacity allocation may be an important cognitive variable mediating developmental differences in basic information processing skills, and may underlie age trends found in performance of certain complex cognitive tasks.     

Compensatory processing during rule-based category learning in older adults

Healthy older adults typically perform worse than younger adults at rule-based category learning, but better than patients with Alzheimer’s or Parkinson’s disease. To further investigate aging’s effect on rule-based category learning, we monitored event-related potentials (ERPs) while younger and neuropsychologically typical older adults performed a visual category-learning task with a rule-based category structure and trial-by-trial feedback. Using these procedures, we previously identified ERPs sensitive to categorization strategy and accuracy in young participants. In addition, previous studies have demonstrated the importance of neural processing in the prefrontal cortex and the medial temporal lobe for this task. In this study, older adults showed lower accuracy and longer response times than younger adults, but there were two distinct subgroups of older adults. One subgroup showed near-chance performance throughout the procedure, never categorizing accurately. The other subgroup reached asymptotic accuracy that was equivalent to that in younger adults, although they categorized more slowly. These two subgroups were further distinguished via ERPs. Consistent with the compensation theory of cognitive aging, older adults who successfully learned showed larger frontal ERPs when compared with younger adults. Recruitment of prefrontal resources may have improved performance while slowing response times. Additionally, correlations of feedback-locked P300 amplitudes with category-learning accuracy differentiated successful younger and older adults. Overall, the results suggest that the ability to adapt one’s behavior in response to feedback during learning varies across older individuals, and that the failure of some to adapt their behavior may reflect inadequate engagement of prefrontal cortex.     

The interactive effects of age,education, and BMI on cognitive functioning

We examined the moderating effects of age and cognitive reserve on the relationship between body mass index (BMI) and processing speed, executive function, and working memory based on the literature suggesting that obese individuals perform more poorly on measures of these abilities. Fifty-six healthy, dementia-free community-dwelling older (mean age 65.72 ± 7.40) and younger (mean age 21.10 ± 2.33) adults completed a neuropsychological battery and reported height and weight. Mixed effects models were used to evaluate the interactive effects of age, education (a proxy for cognitive reserve), and BMI on cognitive scores. Higher education was protective for executive deficits in younger, but not older adults. Age differences in executive functions were reduced at higher education levels but increased in individuals with higher BMI. Results suggest the inter-relationships between cognitive reserve – as measured by education – and BMI differ across age, and that obesity may accelerate the cognitive aging process.     

Aging and attentional guidance during visual search: functional neuroanatomy by positron emission tomography

Positron emission tomography (PET) was used to examine adult age differences in neural activation during visual search. Target detection was less accurate for older adults than for younger adults, but both age groups were successful in using color to guide attention to a subset of display items. Increasing perceptual difficulty led to greater activation of occipitotemporal cortex for younger adults than for older adults, apparently as the result of older adults maintaining higher levels of activation within the easier task conditions. The results suggest that compensation for age-related decline in the efficiency of occipitotemporal cortical functioning was implemented by changes in the relative level of activation within this visual processing pathway, rather than by the recruitment of other cortical regions.     

Exploring collaborative problem solving in adulthood

Collaborative problem solving occurs in situations in which two or more individuals cooperate in appraising, representing, and solving a variety of cognitive tasks. Collaborative groups are the context for much everyday cognitive activity in adulthood. Collaboration has been explored as a means through which older adults may maintain high levels of performance, perhaps compensating for individual-level cognitive and neurological decline. This study explored the effects of collaboration (group size) and adult age on solving both fixed- and unrestricted-alternatives 20 Questions tasks. Younger (M=24.3 years) and older (M=67.9 years) adults were randomly assigned to one of three homogeneous group size conditions: individuals, dyads, and tetrads. Results indicated some dissociation between individual-level performance (poorer for older adults) and collaborative performance (better for older adults). For the fixed-alternatives task, older adults produced more of the relatively inefficient hypothesis-scanning questions than did younger adults. In contrast, older collaborative groups produced more of the efficient constraint-seeking questions than hhpothesis-scanning questions, and an amount equivalent to that of younger adults. Overall performance for the difficult unrestricted-alternatives task was less efficient for both younger and older adults. The roles of task type, group characteristics, and adult age are discussed.     

Effects of age simulation and age on motor sequence learning: Interaction of age-related cognitive and motor decline

Aging is known to lead to decrements in sensory and cognitive functioning and motor performance. The purpose of the present experiment was twofold: a) We assessed the influence of wearing an age simulation suit on motor sequence learning, cognitive speed tasks and far visual acuity in healthy, younger adults. b) We evaluated the interaction of cognitive aging and declining motor sequence learning in older adults. In a between-subjects design we tested 11 younger adults (M_age = 23.6 years) without the age suit, 12 younger adults wearing the age suit (M_age = 23.2 years), and 23 older adults (M_age = 72.6 years). All participants learned a simple, spatial-temporal movement sequence on two consecutive days, and we assessed perceptual processing speed (Digit Symbol Substitution test and Figural Speed test) and far visual acuity. Wearing an age simulation suit neither affected the learning of the simple motor sequence nor the performance at the cognitive speed tasks in younger adults. However, far visual acuity suffered from wearing the suit. Younger adults with and without the suit showed better motor sequence learning compared to older adults. The significant correlations between the cognitive speed tests and the motor learning performance in older adults indicated that cognitive aging partially explains some of the variance in age-related motor learning deficits.     

Autobiographical memory specificity predicts social problem-solving ability in old and young adults

Based on recent research with young, depressed adults, age-related cognitive declines and decreased autobiographical specificity were hypothesized to predict poorer social problem-solving ability in older than in younger healthy adults. Priming autobiographical memory (ABM) was hypothesized to improve social problem-solving performance for older adults. Subsequent to cognitive tests, old and young participants' specific ABMs were tested using a cued recall task, followed by a social problem-solving task. The order of the tasks was counterbalanced to test for a priming effect. Autobiographical specificity was related to cognitive ability and predicted social problem-solving ability for both age groups. However, priming of ABM did not improve social problem-solving ability for older or younger adults. This study provides support for the hypothesis that autobiographical memory serves a directive function across the life-span.     

Age-related differences in the use of background layout in visual search

The effect of background layout on visual search performance, and more specifically on the tendency to refixate previously inspected locations and objects, was investigated. Older and younger adults performed a search task in which a background layout or landmark was present or absent in a gaze contingent visual search paradigm. Regardless of age, participants demonstrated fewer refixations when landmarks were present, with older adults showing a larger landmark advantage. This visual search advantage did not come at the cost of saccadic latency. Furthermore, the visual search performance advantage obtained in the presence of a background layout or landmark was observed both for individuals with small and large memory spans.     

Irrelevant sound effects amongst younger and older adults: Objective findings and subjective insights

Two experiments examine the effects of extraneous speech and nonspeech noise on a visual short-term memory task administered to younger and older adults. Experiment 1 confirms an earlier report that playing task-irrelevant speech is no more distracting for older adults than for younger adults (Rouleau & Belleville, 1996), indicating that “irrelevant sound effects” in short-term memory operate in a different manner to recalling targets in the presence of competing speech (Tun, O'Kane, & Wingfield, 2002). Experiment 2 extends this result to nonspeech noise and demonstrates that the result cannot be ascribed to hearing difficulties amongst the older age group, although the data also show that older adults rated the noise as less annoying and uncomfortable than younger adults. Implications for theories of the irrelevant sound effect, and for cognitive ageing, are discussed.