Free testosterone levels, attentional control, and processing speed performance in aging men.

Psychometric measures of processing speed are strong predictors of cognitive functioning with aging; however, the neurobiological mechanisms underlying this association remain unclear. Recently, the authors reported a negative association between calculated free testosterone levels (cEFT) and processing speed in men aged between 50 and 70 years (Martin, Wittert, Burns, & McPherson, 2008). Ex-Gaussian decomposition of reaction time (RT) distributions allows for the robust estimation of skew in the distribution, which may reflect poorer attentional control. In a reanalysis of data from this previous study, the authors examined the associations between age, cEFT levels, and ex-Gaussian parameters derived from four RT tasks as predictors of cognitive functioning performance in 96 middle-to-older aged men. Results indicated that cEFT levels were significantly associated with increased skew in the RT distribution (i.e., the exponential portion) but not with the estimates derived from the Gaussian portion of the curve. Further, path analysis across the entire data set showed that this association was a strong predictor of processing speed performance. Taken together these results suggest that cEFT levels moderate cognitive functioning performance in males via attentional control processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distinguishing response conflict and task conflict in the Stroop task: Evidence from ex-Gaussian distribution analysis.

It has been suggested that performance in the Stroop task is influenced by response conflict as well as task conflict. The present study investigated the idea that both conflict types can be isolated by applying ex-Gaussian distribution analysis which decomposes response time into a Gaussian and an exponential component. Two experiments were conducted in which manual versions of a standard Stroop task (Experiment 1) and a separated Stroop task (Experiment 2) were performed under task-switching conditions. Effects of response congruency and stimulus bivalency were used to measure response conflict and task conflict, respectively. Ex-Gaussian analysis revealed that response conflict was mainly observed in the Gaussian component, whereas task conflict was stronger in the exponential component. Moreover, task conflict in the exponential component was selectively enhanced under task-switching conditions. The results suggest that ex-Gaussian analysis can be used as a tool to isolate different conflict types in the Stroop task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evidence for higher reaction time variability for children with ADHD on a range of cognitive tasks including reward and event rate manipulations.

Objective: The purpose of the research study was to examine the manifestation of variability in reaction times (RT) in children with attention deficit hyperactivity disorder (ADHD) and to examine whether RT variability presented differently across a variety of neuropsychological tasks, was present across the two most common ADHD subtypes, and whether it was affected by reward and event rate (ER) manipulations. Method: Children with ADHD-combined type (n = 51), ADHD-predominantly inattentive type (n = 53), and 47 controls completed five neuropsychological tasks (Choice Discrimination Task, Child Attentional Network Task, Go/No-Go task, Stop Signal Task, and N-back task), each allowing trial-by-trial assessment of RTs. Multiple indicators of RT variability including RT standard deviation, coefficient of variation and ex-Gaussian tau were used. Results: Children with ADHD demonstrated greater RT variability than controls across all five tasks as measured by the ex-Gaussian indicator tau. There were minimal differences in RT variability across the ADHD subtypes. Children with ADHD also had poorer task accuracy than controls across all tasks except the Choice Discrimination task. Although ER and reward manipulations did affect children's RT variability and task accuracy, these manipulations largely did not differentially affect children with ADHD compared to controls. RT variability and task accuracy were highly correlated across tasks. Removing variance attributable to RT variability from task accuracy did not appreciably affect between-groups differences in task accuracy. Conclusions: High RT variability is a ubiquitous and robust phenomenon in children with ADHD. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Word frequency, repetition, and lexicality effects in word recognition tasks: Beyond measures of central tendency.

Response time (RT) distributions obtained from 3 word recognition experiments were analyzed by fitting an ex-Gaussian function to the empirical data to determine the main effects and interactive influences of word frequency, repetition, and lexicality on the nature of the underlying distributions. The ex-Gaussian analysis allows one to determine if a manipulation simply shifts the response time (RT) distribution, produces a skewing of the RT distribution, or both. In contrast to naming performance, the lexical decision results indicated that the main effects and interactions of word frequency, repetition, and lexicality primarily reflect increased skewing of the RT distributions, as opposed to simple shifts of the RT distributions. The implications of the results were interpreted within a hybrid 2-stage model of lexical decision performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

What are the shapes of response time distributions in visual search?

Many visual search experiments measure response time (RT) as their primary dependent variable. Analyses typically focus on mean (or median) RT. However, given enough data, the RT distribution can be a rich source of information. For this paper, we collected about 500 trials per cell per observer for both target-present and target-absent displays in each of three classic search tasks: feature search, with the target defined by color; conjunction search, with the target defined by both color and orientation; and spatial configuration search for a 2 among distractor 5s. This large data set allows us to characterize the RT distributions in detail. We present the raw RT distributions and fit several psychologically motivated functions (ex-Gaussian, ex-Wald, Gamma, and Weibull) to the data. We analyze and interpret parameter trends from these four functions within the context of theories of visual search. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manual and saccadic reaction time with constant and variable preparatory intervals in schizophrenia.

Saccadic reaction time (RT) has been shown to be unimpaired in schizophrenia. Could this be due to its not requiring controlled information processing? The authors gave 49 schizophrenia patients and 34 controls manual and saccadic RT tasks with preparatory intervals of 1, 3, and 5 s given in regular and irregular sequences. If saccades require mainly automatic processes, they should not be affected by variations in the preparatory interval that are mediated by controlled processing. The manual task showed typical slower RT and larger preparatory interval effects in patients than in controls. Although the saccadic task showed significant effects of both the preparatory interval and the preparatory interval on the preceding trial similar in kind to those in manual RT, there were no group differences in these or in RT. The results are attributed to greater stimulus-response compatibility in the saccadic task, which puts fewer demands on working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factors Influencing Stroop Performance in Schizophrenia.

Recent studies suggest that individuals with schizophrenia show enhanced facilitation but similar interference in reaction times (RTs), compared with control participants, combined with increased error interference. This study examined the relationship between errors and RTs on the Stroop task among individuals with schizophrenia. The authors examined performance on a speeded Stroop task, designed to increase errors, in 29 individuals with schizophrenia and 29 nonpatient control participants. The authors also analyzed color-naming and word-reading estimates from process dissociation analyses. The findings suggest that a lack of increased RT interference among patients (compared with control participants) is not solely due to the increased number of errors they produce in the incongruent condition but is also influenced by a greater impact of the word even in the neutral condition. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spoken numbers versus Arabic numerals: Differential effects on adults' multiplication and addition.

J.-A. LeFevre, Q. Lei, B. L. Smith-Chant, and D. B. Mullins (2001) examined effects of auditory versus Arabic visual presentation formats on performance of simple multiplication. They observed a smaller problem-size effect (response time [RT] increases with numerical size) with auditory stimuli compared with Arabic stimuli. If this arises during problem encoding, as opposed to during subsequent calculation processes, the authors would expect comparable Format × Problem Size interactions for both multiplication and addition. For multiplication, the authors replicated the finding of a smaller problem-size effect for auditory stimuli than for Arabic stimuli, but found the opposite pattern for addition whereby the problem-size effect was larger with auditory stimuli than with Arabic stimuli. Decomposition of mean RT into its ex-Gaussian components, μ and τ, demonstrated that the triple interaction arose entirely in connection with τ. This suggests that the effects of auditory versus Arabic format on RT substantially reflected format-related shifts in the use of procedural strategies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociations between reaction times and temporal order judgments: A diffusion model approach.

A diffusion model for simple reaction time (RT) and temporal order judgment (TOJ) tasks was developed to account for a commonly observed dissociation between these 2 tasks: Most stimulus manipulations (e.g., intensity) have larger effects in RT tasks than in TOJ tasks. The model assumes that a detection criterion determines the level of sensory evidence needed to conclude that a stimulus has been presented. Analysis of the performance that would be achieved with different possible criterion settings revealed that performance was optimal with a lower criterion setting for the TOJ task than for the RT task. In addition, the model predicts that effects of stimulus manipulations should increase with the size of the detection criterion. Thus, the model suggests that commonly observed dissociations between RT and TOJ tasks may simply be due to performance optimization in the face of conflicting task demands. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The locus of dual-task interference: Psychological refractory effects on movement-related brain potentials.

Sought to measure the motor potentials for each of 2 concurrent tasks and to use these measurements to identify the locus of dual-task interference. Lateralized readiness potentials (LRPs) were measured in the psychological refractory period paradigm, in which a separate response is required to each of 2 successive signals. As the interval between the signals decreased, the 2 reaction time (RT) tasks increasingly overlapped and the 2nd RT was prolonged. The LRP for the 2nd task was also delayed but maintained a constant temporal relation with the 2nd RT and sometimes preceded the 1st-task RT. The results indicate that (1) independent measures of the LRP can be obtained for each of 2 concurrent tasks, (2) slowing of the 2nd task was caused by a delay in processes that precede LRP onset, and (3) the 1st task may cease to interfere with the 2nd considerably before producing an overt response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Do the hemispheres watch each other? Evidence for a between-hemispheres performance monitoring.

This study tested the hypothesis that when tasks are complex, response selection and performance monitoring are divided across the hemispheres, and when tasks are simple, response selection and error monitoring are done in the same hemisphere. Using a divided visual field paradigm, the authors presented a target and an interference stimulus, either to the same visual field or to different visual fields, and encouraged error correction. The interference stimulus was timed to interfere with posited error processing. Four tasks were used: bar graph identification, lexical decision, and complex and simple versions of the flankers task. The first three tasks revealed a pattern of contralateral interference, suggesting that error processing occurred in the hemisphere that did not process the initial target. The fourth task showed ipsilateral interference, suggesting that the same hemisphere processed the target and monitored itself. The authors conclude that the pattern of hemispheric cooperation in error processing is affected by task complexity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Individual differences in components of reaction time distributions and their relations to working memory and intelligence.

The authors bring together approaches from cognitive and individual differences psychology to model characteristics of reaction time distributions beyond measures of central tendency. Ex-Gaussian distributions and a diffusion model approach are used to describe individuals' reaction time data. The authors identified common latent factors for each of the 3 ex-Gaussian parameters and for 3 parameters central to the diffusion model using structural equation modeling for a battery of choice reaction tasks. These factors had differential relations to criterion constructs. Parameters reflecting the tail of the distribution (i.e., τ in the ex-Gaussian and drift rate in the diffusion model) were the strongest unique predictors of working memory, reasoning, and psychometric speed. Theories of controlled attention and binding are discussed as potential theoretical explanations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discretionary task interleaving: Heuristics for time allocation in cognitive foraging.

When participants allocated time across 2 tasks (in which they generated as many words as possible from a fixed set of letters), they made frequent switches. This allowed them to allocate more time to the more productive task (i.e., the set of letters from which more words could be generated) even though times between the last word and the switch decision ("giving-up times") were higher in the less productive task. These findings were reliable across 2 experiments using Scrabble tasks and 1 experiment using word-search puzzles. Switch decisions appeared relatively unaffected by the ease of the competing task or by explicit information about tasks' potential gain. The authors propose that switch decisions reflected a dual orientation to the experimental tasks. First, there was a sensitivity to continuous rate of return--an information-foraging orientation that produced a tendency to switch in keeping with R. F. Green's (1984) rule and a tendency to stay longer in more rewarding tasks. Second, there was a tendency to switch tasks after subgoal completion. A model combining these tendencies predicted all the reliable effects in the experimental data. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Divided attention in youth-onset psychosis and attention deficit/hyperactivity disorder.

The authors used pupillary dilations to test whether divided attention deficits in youth-onset psychosis and attention deficit/hyperactivity disorder (ADHD) were because of limitations in recruitment of cognitive resources or abnormalities in attention allocation. Eight- to 19-year-olds with youth-onset psychosis or ADHD were administered a divided attention test consisting of an auditory digit span (DS) task and a simple visual response time (RT) task. In 4 conditions, participants performed neither (no task), 1 (DS or RT only), or both tasks (dual). Dependent variables were DS accuracy, RT, and pupillary dilation to digits as an estimate of recruitment of cognitive resources. The authors found no evidence for an abnormal attention strategy in either disorder. Instead, results were consistent with the hypothesis that both clinical groups have limitations in resource recruitment. These limitations were more severe in psychosis than in ADHD. Findings indicate that both clinical groups had difficulties in regulating physiological arousal on a moment-to-moment basis in accordance with task demands. Findings also demonstrate the importance of taking into account difficulties that constrain performance on simple tasks before interpreting impairments on complex tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Task set switching in schizophrenia.

The authors used a task-switching paradigm to investigate set shifting ability in schizophrenia. This paradigm included 2 choice reaction time (RT) tasks: up–down and right–left. Switching tasks were associated with costs (i.e., longer RT in task-switch trials than in task-repetition trials); patients responded more slowly than controls and suffered greater switching costs, were as efficient as controls in engaging in an upcoming task set, and were faster than controls in disengaging from the previous task set. There were indications that patients quickly forgot what each keypress indicated, making it necessary for them to acquire response meaning information anew in each trial. To test this notion, the authors subsequently tested normal participants in conditions in which response meaning information needed to be acquired anew in each trial. These participants produced a pattern of switching costs resembling that of patients. Results suggest that set switching difficulties in schizophrenia, as exhibited in the present paradigm, reflect poor memory for task context information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Working Memory Capacity, Indirect Semantic Priming, and Stroop Interference: Pattern of Interindividual Prefrontal Performance Differences in Healthy Volunteers.

Using neuropsychological models of prefrontal function, the authors investigated the pattern of interindividual prefrontal performance differences in healthy volunteers. Using a correlation and an extreme group approach, they compared verbal and visuospatial working memory capacity with performance on the Stroop interference task as a measure of executive control and on the direct and indirect semantic priming tasks as a measure of semantic access. Subjects with low visuospatial working memory capacity exhibited increased Stroop interference Subjects with low verbal memory capacity showed increased priming and Stroop interference only. The study shows that prefrontal functioning varies interindividually, forming patterns of performance differences. These findings suggest that working memory, executive control, and semantic retrieval are functionally related to some extent. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Emotion and working memory: Evidence for domain-specific processes for affective maintenance.

Working memory is comprised of separable subsystems for visual and verbal information, but what if the information is affective? Does the maintenance of affective information rely on the same processes that maintain nonaffective information? The authors address this question using a novel delayed-response task developed to investigate the short-term maintenance of affective memoranda. Using selective interference methods the authors find that a secondary emotion-regulation task impaired affect intensity maintenance, whereas secondary cognitive tasks disrupted brightness intensity maintenance, but facilitated affect maintenance. Additionally, performance on the affect maintenance task depends on the valence of the maintained feeling, further supporting the domain-specific nature of the task. The importance of affect maintenance per se is further supported by demonstrating that the observed valence effects depend on a memory delay and are not evident with simultaneous presentation of stimuli. These findings suggest that the working memory system may include domain-specific components that are specialized for the maintenance of affective memoranda. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Investigation of the robust rank-order test for non-normal populations with unequal variances: The case of reaction time.

Evaluated the performance of the robust rank-order (Fligner-Policello) test of treatment effects for populations with unequal variances. Both symmetric (normal) and skewed (ex-Gaussian) distributions were examined. The ex-Gaussian distribution is particularly relevant because it is representative of skewed distributions found in experimental psychology, most notably reaction time data. Results indicate that when testing the hypothesis of equal medians for the symmetric distribution, the Fligner-Policello test is conservative, whereas it performs inconsistently for the skewed population. In light of the findings, the authors discuss the various options presently available to researchers confronted with unequal variances and skewed data, including a discussion of whether testing for treatment effects for populations with unequal variances is of practical relevance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Distinguishing common and task-specific processes in word identification: A matter of some moment?

The same 500 words were presented in 6 different word identification tasks (Experiment 1: lexical decision, semantic categorization, and 3 speeded naming tasks; Experiment 2: delayed naming). Reaction time (RT distributions were estimated for each task and analyses tested for the effects of word frequency and animacy on various parameters of the RT distribution. Low frequency words yielded more skewed distributions than high frequency words in all tasks except delayed naming. The differential skew was most marked for tasks that required lexical discrimination. The semantic categorization task yielded highly skewed distributions for all words, but the word frequency effect was due to shifts in the location of the RT distributions rather than changes in skew. The results are used to evaluate the relative contributions of a common lexical access process and task-specific processes to performance in lexical discrimination and naming tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Collective induction without cooperation? Learning and knowledge transfer in cooperative groups and competitive auctions.

There is strong evidence that groups perform better than individuals do on intellective tasks with demonstrably correct solutions. Typically, these studies assume that group members share common goals. The authors extend this line of research by replacing standard face-to-face group interactions with competitive auctions, allowing for conflicting individual incentives. In a series of studies involving the well-known Wason selection task, they demonstrate that competitive auctions induce learning effects equally impressive as those of standard group interactions, and they uncover specific and general knowledge transfers from these institutions to new reasoning problems. The authors identify payoff feedback and information pooling as the driving factors underlying these findings, and they explain these factors within the theoretical framework of collective induction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)