Joshua Sandry

Subjective Cognitive Fatigue in Multiple Sclerosis Depends on Task Length

Objective: The objective of this paper is to investigate the interrelationship between subjective and objective cognitive fatigue, information processing domain [processing speed (PS) vs. working memory (WM)], cognitive load (high vs. low), and time on task in Multiple Sclerosis (MS). Methods: Thirty-two MS participants and 24 healthy controls completed experimental tasks in both the PS and WM domains with different levels of cognitive load. Subjective cognitive fatigue was measured using a visual analog scale at baseline and at multiple time points throughout the experiment. Results: A mixed model ANOVA revealed that subjective cognitive fatigue was higher for the PS task, increased across time, and was higher in the MS group. These findings were qualified by an interaction demonstrating that the MS group showed a steeper increase in subjective cognitive fatigue over time than the healthy control group. Subjective and objective (i.e., performance) cognitive fatigue were not correlated. Conclusion: In this study, subjective and objective cognitive fatigue appears to be independent and cognitive fatigue does not depend on cognitive load. Subjective cognitive fatigue increased with time on task and subjective cognitive fatigue increased more steeply for the MS group. These data suggest that cognitive fatigue in MS is a function of time, that is, the longer participants were engaged in a cognitive task, the more likely it was for them to report increases in cognitive fatigue.

Prevalence-based decisions undermine visual search

In visual search, observers make decisions about the presence or absence of a target based on their perception of a target during search. The present study investigated whether decisions can be based on observers’ expectation rather than perception of a target. In Experiment 1, participants were allowed to make target-present responses by clicking on the target or, if the target was not perceived, a target-present button. Participants used the target-present button option more frequently in difficult search trials and when target prevalence was high. Experiment 2 and 3 employed a difficult search task that encouraged the use of prevalence-based decisions. Target presence was reported faster when target prevalence was high, indicating that decisions were, in part, cognitive, and not strictly perceptual. A similar pattern of responses were made even when no targets appeared in the search (Experiment 3). The implication of these prevalence-based decisions for visual search models is discussed.

Intentional inferences are not more likely than unintentional ones: Some evidence against the intentionality bias hypothesis

ABSTRACT We conducted a study to test the hypothesis that inferences about intentionality are biased toward an intentional interpretation. Contrary to previous research, participants were no more likely to judge ambiguous actions as intentional in a speeded compared to an unspeeded condition. Further, participants were faster to respond and more consistent in responding to unintentional rather than intentional actions.

Working memory capacity links cognitive reserve with long-term memory in moderate to severe TBI: a translational approach

Traumatic brain injury (TBI) can have devastating negative consequences on an individuals’ ability to remember information; however, there is variability among memory impairment resulting from TBI. Some individuals exhibit long-term memory (LTM) impairment while others do not. This variability has been explained, at least in part, by the theory of cognitive reserve (CR). The theory suggests that individuals who have spent significant time engaged in intellectually enriching activities (higher CR) are better able to withstand LTM impairment despite neurological injury. The cognitive mechanisms that underlie this relationship are not well-specified. Recent evidence suggests that working memory (WM) capacity may be one mediating variable that can help explain how/why cognitive reserve (CR) protects against LTM impairment. The present research tested this hypothesis in a sample of fifty moderate to severe TBI patients. Specific neuropsychological tests were administered to estimate CR, LTM and WM. The results were congruent with a recent theoretical model that implicates WM capacity as a mediating variable in the relationship between CR and LTM (Sobel’s Zxa0=xa02.62, pxa0=xa00.009). These data corroborate recent findings in an alternate neurological population and suggest that WM is an underlying mechanism of CR. Additional research is necessary to establish whether (1) WM is an important individual difference variable to include in memory rehabilitation trials and (2) to determine whether rehabilitation and treatment strategies that specifically target WM may also lead to complimentary improvements on diagnostic tests of delayed LTM in TBI and other memory impaired populations.

False feedback increases detection of low-prevalence targets in visual search.

Many critical search tasks, such as airport and medical screening, involve searching for targets that are rarely present. These low-prevalence targets are associated with extremely high miss rates Wolfe, Horowitz, & Kenner (Nature, 435, 439–440, 2005). The inflated miss rates are caused by a criterion shift, likely due to observers attempting to equate the numbers of misses and false alarms. This equalizing strategy results in a neutral criterion at 50xa0% target prevalence, but leads to a higher proportion of misses for low-prevalence targets. In the present study, we manipulated participants’ perceived number of misses through explicit false feedback. As predicted, the participants in the false-feedback condition committed a higher number of false alarms due to a shifted criterion. Importantly, the participants in this condition were also more successful in detecting targets. These results highlight the importance of perceived prevalence in target search tasks.

Working memory mediates the relationship between intellectual enrichment and long-term memory in multiple sclerosis: an exploratory analysis of cognitive reserve.

Some individuals with multiple sclerosis (MS) show decrements in long-term memory (LTM) while other individuals do not. The theory of cognitive reserve suggests that individuals with greater pre-morbid intellectual enrichment are protected from disease-related cognitive decline. How intellectual enrichment affords this benefit remains poorly understood. The present study tested an exploratory meditational hypothesis whereby working memory (WM) capacity may mediate the relationship between intellectual enrichment and verbal LTM decline in MS. Intellectual enrichment, verbal LTM, and WM capacity were estimated with the Wechsler Test of Adult Reading and Peabody Picture Vocabulary Test, delayed recall of the Hopkins Verbal Learning Test-Revised and Logical Memory of the Wechsler Memory Scale, and Digit Span Total, respectively. Intellectual enrichment predicted LTM (B=.54; p=.003) and predicted WM capacity (B=.91; p<.001). WM capacity predicted LTM, (B=.44; p<.001) and fully mediated the relationship between intellectual enrichment (B=.24; p=.27) and LTM (B=.33, p=.03), Sobel test, Z=3.31, p<.001. These findings implicate WM capacity as an underlying mechanism of cognitive reserve and are an initial first step in understanding the relationship between intellectual enrichment, WM, and LTM in MS.

Evidence for a positive relationship between working-memory capacity and detection of low-prevalence targets in visual search.

Our ability to detect a target in visual search relates to the prevalence of the target, whereby rare targets are missed more than common targets. The current study sought to identify operator characteristics that could account for the higher miss rates associated with rare targets. The results found that working-memory capacity, which is strongly related to attentional control and inhibition of irrelevant information, was significantly correlated with the ability to detect low-prevalence targets. High-capacity observers also exhibited lengthened target-absent responses with rare targets, suggesting that the high-capacity observers were more persistent in their searches than others.

Adaptive Memory: Evaluating Alternative Forms of Fitness-Relevant Processing in the Survival Processing Paradigm

Memory may have evolved to preserve information processed in terms of its fitness-relevance. Based on the assumption that the human mind comprises different fitness-relevant adaptive mechanisms contributing to survival and reproductive success, we compared alternative fitness-relevant processing scenarios with survival processing. Participants rated words for relevancy to fitness-relevant and control conditions followed by a delay and surprise recall test (Experiment 1a). Participants recalled more words processed for their relevance to a survival situation. We replicated these findings in an online study (Experiment 2) and a study using revised fitness-relevant scenarios (Experiment 3). Across all experiments, we did not find a mnemonic benefit for alternative fitness-relevant processing scenarios, questioning assumptions associated with an evolutionary account of remembering. Based on these results, fitness-relevance seems to be too wide-ranging of a construct to account for the memory findings associated with survival processing. We propose that memory may be hierarchically sensitive to fitness-relevant processing instructions. We encourage future researchers to investigate the underlying mechanisms responsible for survival processing effects and work toward developing a taxonomy of adaptive memory.

General Mathematical Ability Predicts PASAT Performance in MS Patients: Implications for Clinical Interpretation and Cognitive Reserve.

OBJECTIVESnThe Paced Auditory Serial Addition Test (PASAT) is used to assess cognitive status in multiple sclerosis (MS). Although the mathematical demands of the PASAT seem minor (single-digit arithmetic), cognitive psychology research links greater mathematical ability (e.g., algebra, calculus) to more rapid retrieval of single-digit math facts (e.g., 5+6=11). The present study evaluated the hypotheses that (a) mathematical ability is related to PASAT performance and (b) both the relationship between intelligence and PASAT performance as well as the relationship between education and PASAT performance are both mediated by mathematical ability.nnnMETHODSnForty-five MS patients were assessed using the Wechsler Test of Adult Reading, PASAT and Calculation Subtest of the Woodcock-Johnson-III. Regression based path analysis and bootstrapping were used to compute 95% confidence intervals and test for mediation.nnnRESULTSnMathematical ability (a) was related to PASAT (β=.61; p<.001) and (b) fully mediated the relationship between Intelligence and PASAT (β=.76; 95% confidence interval (CI95)=.28, 1.45; direct effect of Intelligence, β=.42; CI95=-.39, 1.23) as well as the relationship between Education and PASAT (β=2.43, CI95=.81, 5.16, direct effect of Education, β=.83, CI95=-1.95, 3.61).nnnDISCUSSIONnMathematical ability represents a source of error in the clinical interpretation of cognitive decline using the PASAT. Domain-specific cognitive reserve is discussed.

Cognitive contributions to differences in learning after moderate to severe traumatic brain injury

Introduction: Deficits in learning and memory are commonly observed after traumatic brain injury (TBI); however, the mechanisms underlying such deficits are poorly understood. This study examines the contribution of other cognitive processes in verbal learning after moderate to severe TBI. Adults with TBI who have verbal learning deficits were predicted to perform worse on executive measures than adults who are able to learn. Method: Participants were 51 community-dwelling adult volunteers (age 18–59) with moderate to severe TBI. Injury severity was determined by Glasgow Coma Scale score ≤12 and corroborating information from medical records. Group membership (TBI-learners or TBI-nonlearners) was determined by a learning criterion of perfect recall on 2 consecutive trials within 15 trials on the open-trial Selective Reminding Test. All participants completed a comprehensive neuropsychological test battery. Group differences were examined using independent-samples t tests, and logistic regression was used to determine significant predictors of learning ability. Results: The TBI-learner group performed better than the TBI-nonlearner group most consistently on tasks of executive control and working memory. Results of a logistic regression showed that working memory capacity was the most significant predictor of learning ability after TBI. Conclusions: Working memory significantly influences the ability to learn verbal information after TBI. The documented relationship between working memory and learning will guide the development of more efficacious treatments to rehabilitate learning and memory deficits after TBI.