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.     

Age-differential effects on updating cue information: Evidence from event-related potentials

Recent models on cognitive aging consider the ability to maintain and update context information to be a key source of age-related impairments in various cognitive tasks (Braver & Barch in Neuroscience & Biobehavioral Reviews, 26: 809–817, 2002). Context updating has been investigated with a modified AX-continuous-performance task by comparing performance and brain activity between context-dependent trials (i.e., correct responses require updating of the preceding cue information) and context-independent trials (i.e., correct responses are independent of cue information). We used an event-related potential (ERP) approach to identify sources of age differences in context processing in the early and late processing of cue information. Our behavioral data showed longer latencies and higher error rates on context-dependent than on context-independent trials for older than for younger adults, suggesting age-related impairments in context updating. The ERP data revealed larger P3b amplitudes for context-dependent than for context-independent trials only in younger adults. In contrast, in older adults, P3b amplitudes were more evenly distributed across the scalp and did not differ between context conditions. Interestingly, older but not younger adults were sensitive to changes of cue identity, as indicated by larger P3b amplitudes on cue-change than on cue-repeat trials, irrespective of the actual context condition. We also found a larger CNV on context-dependent than on context-independent trials, reflecting active maintenance of context information and response preparation. The age-differential effects in the P3b suggest that both younger and older adults were engaged in updating task-relevant information, but relied on different information: Whereas younger participants indeed relied on context cues to update and reconfigure the task settings, older adults relied on changes in cue identity, irrespective of context information.     

General slowing in semantic priming and word recognition.

Analyses of lexical decision studies revealed that (a) older (O) adults' mean semantic priming effect was 1.44 times that of younger (Y) adults, (b) regression lines describing the relations between older and younger adults' latencies in related (O = 1.54 Y-112 and unrelated conditions (O = 1.50 Y-93) were not significantly different, and (c) that there was a proportional relation between older and younger adults' priming effects (O = 1.48 Y-2). Analyses of word-naming studies yielded similar results. Analyses of delayed pronunciation data (Balota & Duchek, 1988) revealed that word recognition was 1.47 times slower in older adults, whereas older adults' output processes were only 1.26 times slower. Overall, analyses of whole latencies and durations of component processes provide converging evidence for a general slowing factor of approximately 1.5 for lexical information processing.     

Mind-wandering in younger and older adults: converging evidence from the Sustained Attention to Response Task and reading for comprehension

One mechanism that has been hypothesized to contribute to older adults' changes in cognitive performance is goal neglect or impairment in maintaining task set across time. Mind-wandering and task-unrelated thought may underlie these potential age-related changes. The present study investigated age-related changes in mind-wandering in three different versions of the Sustained Attention to Response Task (SART), along with self-reported mind-wandering during a reading for comprehension task. In the SART, both younger and older adults produced similar levels of faster reaction times before No-Go errors of commission, whereas, older adults produced disproportionate post-error slowing. Subjective self-reports of mind-wandering recorded during the SART and the reading task indicated that older adults were less likely to report mind-wandering than younger adults. Discussion focuses on cognitive and motivational mechanisms that may account for older adults' relatively low levels of reported mind-wandering.     

Lost ability to automatize task performance in old age

Can elderly adults automatize a new task? To address this question, 10 older adults each performed 10,080 training trials over 12 sessions on an easy but novel task. The psychological refractory period (PRP) procedure was then used to evaluate whether this highly practiced task, when presented as task 2 along with an unpracticed task 1, could proceed automatically. If automatic, task 2 processing should bypass the bottleneck and, therefore, not be delayed while central attention is devoted to task 1, yielding little dual-task interference. This is exactly what Maquestiaux, Laguë-Beauvais, Ruthruff, and Bherer (Memory and Cognition 36:1262-1282, 2008) previously observed for almost all younger adults, even with half the training on a more difficult task. Although extensive training reduced older adults’ reaction times to only 307 ms, a value virtually identical to that attained by Maquestiaux et al.’s (Memory and Cognition 36:1262-1282, 2008) younger adults, the highly practiced task 2 was slowed by 485 ms in the dual-task PRP procedure. Such a large slowing in older adults is striking given the easy tasks and massive amounts of practice. These findings demonstrate a qualitative change with age, in which older adults lose the ability to automatize novel tasks, which cannot be attributed merely to generalized cognitive slowing.     

Age and skilled performance: contributions of working memory and processing speed

In this study, we examined the interrelationships among age, working memory (WM), processing speed, and the development of skilled performance. Younger (M=20.5) and older (M=68.9) adults were trained on an alphabet arithmetic task (Haider & Frensch, 1996) administered across three consecutive days. Although older adults were slower than younger adults, both age groups' response latencies decreased as a result of practice. Contrary to expectations, WM and processing speed were significantly correlated with performance late in training. Partial correlations suggested that age differences in performance at the end of training were mediated by individual differences in cognitive processing speed.     

Age-related differences and similarities in dual-task interference

Differences between younger adults (mean age, 20.7 years) and older adults (mean age, 72.7 years) in dual-task performance were examined in 7 experiments in which the overlap between 2 simple tasks was systematically varied. The results were better fit by a task-switching model in which age was assumed to produce generalized slowing than by a shared-capacity model in which age was assumed to reduce processing resources. The functional architecture of task processing appears the same in younger and older adults. There was no evidence for a specific impairment in the ability of older adults to manage simultaneous tasks. There was evidence for both input and output interference, which may be greater in older adults.     

Experimental evidence for differential slowing in the lexical and nonlexical domains

Abstract

Older and younger adults were tested on lexical and nonlexical tasks. When lexical and nonlexical processing were compared across equivalent ranges of task complexity, the degree of age-related slowing in the nonlexical domain was much larger than that observed in the lexical domain. to determine whether this nonlexical disadvantage is specific to older adults or whether it is characteristic of any slow individual, subgroups of fast older and slow young adults were matched on lexical processing speed. Older adults who were fast processors of lexical information were much slower at processing nonlexical information, but this was not true of slow young adults for whom the speed of processing lexical and nonlexical information was equivalent.     

Executive-process interactive control: A unified computational theory for answering 20 questions (and more) about cognitive ageing

Although the effects of ageing on human information processing and performance have been studied extensively, many fundamental questions about cognitive ageing remain to be answered definitively. For example, what are the sources of age-related slowing? How much is working-memory capacity reduced in older adults? Is time-sharing ability lost with age? Answering such questions requires a unified computational theory that characterises the interactive operations of many component mental processes and integrates diverse data on cognitive ageing. Toward fulfilling this requirement, an executive-process interactive control (EPIC) architecture has been extended to model performance of both young and older adults. EPIC models yield accurate accounts of ageing effects on reaction times and accuracy in basic dual-task and working-memory paradigms. From these accounts, it appears that time-sharing ability and working-memory capacity decrease relatively little until after 70 years of age. Before age 70, at least some apparent performance decrements may be attributable to conservative executive processes and inefficient task procedures rather than decreased "hardware" functionality. By clarifying and deepening such insights, unified computational theories like EPIC will help answer many questions about cognitive ageing.     

The attentional demands of encoding and retrieval in younger and older adults: 2. Evidence from secondary task reaction time distributions

Three studies examined the effects of encoding or retrieval on properties of secondary task reaction time (RT) distributions in younger and older adults. Relative to full attention conditions, encoding and retrieval increased secondary task RT medians and standard deviations more for older adults than for younger adults, and the age-related RT increase was most pronounced among the slowest RTs. Hierarchical regression analyses revealed two age-related mechanisms underlying these effects, which were interpreted as cognitive slowing and reductions in attentional resources. Cognitive slowing affects the entire RT distribution regardless of the memory task. By contrast, reduced attentional resources result in very long RTs, especially when the tasks require self-initiated encoding or retrieval operations.     

How general is general slowing? Evidence from the lexical domain

Three analyses are reported that are based on data from 19 studies using lexical tasks and a reduced version of the Hale, Myerson, and Wagstaff (1987) nonlexical data set. The results of Analysis 1 revealed that a linear function with a slope of approximately 1.5 described the relationship between the lexical decision latencies of older (65-75 years) and younger (19-29 years) adults. The results of Analysis 2, based on response latencies from 6 lexical tasks other than lexical decision, revealed a virtually identical linear relationship. In Analysis 3, it was found that performance on nonlexical tasks spanning the same range of task difficulty was described by a significantly steeper regression line with a slope of approximately 2.0. These findings suggest that although general cognitive slowing is observed in both domains, the degree of slowing is significantly greater in the nonlexical domain than in the lexical domain. In addition, these analyses demonstrate how the meta-analytic approach may be used to determine the limits to the external validity of experimental findings.     

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.     

Global increase in response latencies by early middle age: complexity effects in individual performances

Ten young women (age 20 to 22 years) and 10 middle-aged women (age 36 to 44 years) served as subjects in choice reaction time, letter classification, and abstract matching-to-sample tasks. In each of seven conditions, the older group responded more slowly than the younger group. Age differences showed a complexity effect. That is, differences between the latencies of young and old subjects increased as the latency of the young subjects increased. Both linear and power functions accurately described the relation between the latencies of the middle-aged and young adult groups. This was true not only for the relation between average latencies but also for the relation between corresponding quartiles of latency distributions. Similar results were observed at the individual level: All middle-aged subjects showed complexity effects, and, for each middle-aged subject, the relation between her latencies and those of the average young adult was well described by linear and power functions. These findings indicate that age-related slowing is apparent by age 40, and that complexity effects are observable in individual performances. This slowing is global and not specific to particular tasks, as indicated by the fact that the latencies of older adults can be predicted directly from those of younger adults without regard to the nature of the task.     

Item-specific processing reduces false recognition in older and younger adults: Separating encoding and retrieval using signal detection and the diffusion model

Our study examined processing effects in improving memory accuracy in older and younger adults. Specifically, we evaluated the effectiveness of item-specific and relational processing instructions relative to a read-only control task on correct and false recognition in younger and older adults using a categorized-list paradigm. In both age groups, item-specific and relational processing improved correct recognition versus a read-only control task, and item-specific encoding decreased false recognition relative to both the relational and read-only groups. This pattern was found in older adults despite overall elevated rates of false recognition. We then applied signal-detection and diffusion-modeling analyses, which separately utilized recognition responses and the latencies to those responses to estimate contributions of encoding and monitoring processes on recognition decisions. Converging evidence from both analyses demonstrated that item-specific processing benefits to memory accuracy were due to improvements of both encoding (estimates of d′ and drift rate) and monitoring (estimates of lambda and boundary separation) processes, and, importantly, occurred similarly in both younger and older adults. Thus, older and younger adults showed similar encoding-based and test-based benefits of item-specific processing to enhance memory accuracy.     

Information selectivity in decision making by younger and older adults

Past research has demonstrated that older adults are more likely than younger adults to exhibit information selectivity in decision making. Two alternative explanations have been proposed to account for this age difference. One explanation attributes the increase in information selectivity to older adults' reliance on prior knowledge, whereas the other explanation suggests that it reflects reduced information processing capacity. The aim of this research was to explore the latter explanation by controlling for experiential factors and varying the cognitive demands involved in decision making. Specifically, participants were faced with unfamiliar decision problems, and had to base their decisions on the available information in order to reach a desired goal. In Experiment 1 younger and older participants were required to play a game involving chance. The outcome payoff was varied between three conditions (approach, avoidance, and control). The results indicated that both the younger and the older participants based their decisions on payoff, though the older participants did so to a lesser extent. In Experiment 2 younger and older participants performed a similar decision task but with higher cognitive demands. Specifically, the decision‐making task included two dimensions of information, outcome probability and outcome payoff. The results showed that the younger participants based their decisions on probability and payoff whereas the older participants based their decisions on probability alone. In Experiment 3 younger and older participants made decisions in a sale context and received instructional cue to incorporate payoff information in their decisions. As before, the younger participants utilized probability and payoff, whereas the older participants based their decisions only on probability information. The findings are discussed in terms of age differences in information‐processing capacity, metacognition, motivation, and goal‐setting.     

General cognitive slowing in the nonlexical domain: an experimental validation.

Older and younger adults were tested on 4 nonlexical tasks: choice reaction time, letter classification, mental rotation, and abstract matching. A positively accelerated relation was observed between older and younger adults' latencies. Consistent with general slowing, the relation observed with the same subjects in each condition was more than 3 times as precise as in a comparable meta-analysis. Further analyses compared the ability of various models to describe the present data and also to predict the data on the basis of parameters estimated from a previous meta-analysis. Compared with linear models, the information-loss and overhead models provided more accurate accounts of general cognitive slowing in the nonlexical domain.     

Aging,Task Complexity,and Efficiency Modes: The Influence of Working Memory Involvement on Age Differences in Response Times for Verbal and Visuospatial Tasks

ABSTRACT

We examined the information-processing functions (response-time × load) of younger and older adults for two verbal and one visuo-spatial task; each task was implemented in a baseline and a high-complexity condition. Heightened complexity transformed the baseline functions in either an additive or a multiplicative fashion. The processing efficiency of older adults was defined as the old-young ratio of the slopes of the load functions. Three levels of efficiency could be distinguished. The first level, with an age-related slowing factor of about 1.2, consisted of low-complexity verbal processing and additive-complexity verbal processing. The second level, associated with a slowing factor of about 1.6, consisted of a mixture of verbal-high-multiplicative-complexity processing and visuo-spatial-low-complexity processing. The third level, with a slowing factor of about 4, consisted of visuo-spatial processing of high multiplicative complexity. The results go against any common factor theory of aging. Instead, they suggest that a shift from a higher to a lower mode of efficiency is triggered by a greater degree of working memory involvement.     

Aging, task complexity, and efficiency modes: the influence of working memory involvement on age differences in response times for verbal and visuospatial tasks

We examined the information-processing functions (response-time x load) of younger and older adults for two verbal and one visuo-spatial task; each task was implemented in a baseline and a high-complexity condition. Heightened complexity transformed the baseline functions in either an additive or a multiplicative fashion. The processing efficiency of older adults was defined as the old-young ratio of the slopes of the load functions. Three levels of efficiency could be distinguished. The first level, with an age-related slowing factor of about 1.2, consisted of low-complexity verbal processing and additive-complexity verbal processing. The second level, associated with a slowing factor of about 1.6, consisted of a mixture of verbal-high-multiplicative-complexity processing and visuo-spatial-low-complexity processing. The third level, with a slowing factor of about 4, consisted of visuo-spatial processing of high multiplicative complexity. The results go against any common factor theory of aging. Instead, they suggest that a shift from a higher to a lower mode of efficiency is triggered by a greater degree of working memory involvement.     

Older age, traumatic brain injury, and cognitive slowing: some convergent and divergent findings

Reaction time (RT) meta-analyses of cognitive slowing indicate that all stages of processing slow equivalently and task independently among both older adults (J. Cerella & S. Hale, 1994) and adults who have suffered a traumatic brain injury (TBI; F. R. Ferraro, 1996). However, meta-analyses using both RT and P300 latency have revealed stage-specific and task-dependent changes among older individuals (T. R. Bashore, K. R. Ridderinkhof, & M. W. van der Molen, 1998). Presented in this article are a meta-analysis of the effect of TBI on processing speed, assessed using P300 latency and RT, and a qualitative review of the literature. They suggest that TBI induces differential slowing. Similarities in the effects of older age and TBI on processing speed are discussed and suggestions for future research on TBI-induced cognitive slowing are offered.     

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.