Standard Deviation Of Reaction Time Research Articles

Acute Effects of Tai Chi Chuan, Coordination and Aerobic Exercise on Attention in Elderly Individuals

This study examined the effects of 3 different acute exercise modes on sustained attention in elderly adults. Twelve experienced male Tai Chi Chuan (TCC) practitioners were assigned to: TCC, coordination program and ergometer cycling. Each exercise session lasted for 30 minutes. Before and after the exercise a 14 min Continues Performance Test (CPT) was conducted to evaluate sustained attention. Results: After TCC a value for attentiveness (Detectability) improved significantly with p=0.01. Decreasing commission mistakes (p=0.06) and hit reaction time (p=0.09) showed a tendency for higher attention levels. Hit reaction time value (p=0.026) and hit reaction time standard deviation (p=0.002) reduced significantly after the coordination session. Commission mistakes decreased significantly (p=0.031) after ergometer cycling. These results demonstrate that each exercise mode influences attention markers differently; Coordinative challenging exercises are more beneficial for attention; TCC in specific for attentiveness and inhibition; and aerobic training for inhibition.

Effects of stimulus intensity and auditory white noise on human somatosensory cognitive processing: a study using event-related potentials

Exposure to auditory white noise has been shown to facilitate cognitive function. This phenomenon is often called stochastic resonance, and a moderate amount of auditory noise has been suggested to benefit individuals in hypodopaminergic states. Previous studies using psychophysic methods reported that stochastic resonance was sensitive to stimulus intensity; however, the relationship between neural activities elicited by different stimulus intensities and auditory white noise has not yet been clarified Thus, the present study aimed to investigate the effects of stimulus intensity (Experiment 1) and auditory white noise (Experiment 2) on behavioral data (reaction time (RT), the standard deviation of RT, and error rates), and the N140 and P300 components of event-related potentials (ERPs) in somatosensory Go/No-go paradigms. The subjects had to respond to the somatosensory stimuli by pressing a button with their right thumb only after presentation of the Go stimulus. In Experiment 1 with four different stimulus intensity levels, the peak latencies of N140 and P300 became shorter, and the peak amplitudes of N140 and P300 were enhanced with increases in stimulus intensity. In Experiment 2 with weak and mild intensities under auditory white noise and control conditions, the amplitudes of Go-P300 and No-go-P300 were enhanced by white noise, irrespective of weak and mild intensities, during Go/No-go paradigms. Auditory white noise did not significantly affect the amplitude of N140 or the latencies of N140 and P300. These results suggest the presence of a characteristic cross-modal stochastic resonance in neural substrates utilizing somatosensory ERPs.

Genome-wide association study reveals novel genetic locus associated with intra-individual variability in response time

Intra-individual response time variability (IIRTV) is proposed as a viable endophenotype for many psychiatric disorders, particularly attention-deficit hyperactivity disorder (ADHD). Here we assessed whether IIRTV was associated with common DNA variation genome-wide and whether IIRTV mediated the relationship between any associated loci and self-reported ADHD symptoms. A final data set from 857 Australian young adults (489 females and 368 males; Mage = 22.14 years, SDage = 4.82 years) who completed five response time tasks and self-reported symptoms of ADHD using the Conners’ Adult ADHD Rating Scale was used. Principal components analysis (PCA) on these response time measures (standard deviation of reaction times and the intra-individual coefficient of variation) produced two variability factors (labelled response selection and selective attention). To understand the genetic drivers of IIRTV we performed a genome-wide association analysis (GWAS) on these PCA-derived indices of IIRTV. For the selective attention variability factor, we identified one single-nucleotide polymorphism (SNP) attaining genome-wide significance; rs62182100 in the HDAC4 gene located on chromosome 2q37. A bootstrapping mediation analysis demonstrated that the selective attention variability factor mediated the relationship between rs62182100 and self-reported ADHD symptoms. Our findings provide the first evidence of a genome-wide significant SNP association with IIRTV and support the potential utility of IIRTV as a valid endophenotype for ADHD symptoms. However, limitations of this study suggest that these observations should be interpreted with caution until replication samples become available.

Ex-Gaussian, Frequency and Reward Analyses Reveal Specificity of Reaction Time Fluctuations to ADHD and Not Autism Traits

Both attention-deficit/hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) have been linked to increased reaction time variability (RTV), a marker of attentional fluctuation. Here we test whether specificity to either trait emerges when we examine (1) detailed ex-Gaussian and frequency RTV subcomponents, (2) effects while controlling for the other trait and (3) improvement in the RTV measures following rewards or a faster event rate. 1110 children aged 7–10 years from a population-based sample completed a Go/No-Go task under three conditions (slow, fast and incentives). We measured RTV with standard deviation of RT (SDRT), ex-Gaussian distribution measures (Sigma and Tau), RT fluctuations in cycles of ~14–90 s in all conditions (Slow-4 and Slow-5), and RT fluctuations in cycles of 2–14 s in the fast condition (Slow-2 and Slow-3). Parent-rated ADHD and ASD traits were obtained. All refined RTV components were linked to ADHD traits only and not to ASD traits, while Sigma did not relate to either trait. Although both ADHD and ASD social-communication traits were associated with SDRT, the association with social-communication impairments disappeared when controlling for ADHD traits. A reward-induced improvement in RTV measures, indicating malleability, emerged in relation to ADHD traits but not ASD traits. Under closer inspection, specificity emerges of high RTV to ADHD traits. For the clinician, our findings indicate that attentional fluctuation in children with high ASD traits may be due to co-occurring ADHD traits and emphasise how the effectiveness of rewards does not generalise from ADHD to ASD traits.

Relations between a laboratory-based sustained attention task and traffic violations in an Iranian sample of drivers

The role of cognitive abilities regarding driver behavior is crucially important in the occurrence of traffic violations and preventing tragic motor vehicle collisions. Sustained attention is one cognitive ability that may contribute to safe driving behavior. The present study investigated the relation between sustained attention and traffic violations. One hundredand one Iranian male drivers (age: M = 37.17, SD = 8.37) with at least 2 years driving experience voluntarily participated in the study. Participants were categorized into two groups based on the number of driving rule violations they committed over the last 2 years (n = 48 clean record, n = 53 violators). Sustained attention was measured by performance on the Conjunctive Continuous Performance Task (CCPT). Four CCPT performance measures were computed: (1) Mean reaction time for correct responses (M-RT); (2) standard deviation of reaction times for correct responses (SD-RT); (3) percent of omission errors (failure to respond to target stimulus); (4) percent of commission errors (identification of a non-target stimulus as target). Results showed after controlling for age and education, there was a significant group difference on M-RT, indicating that individuals with no traffic violations had faster reaction times as compared to those who had 1 or more traffic violations. No effect of group on any of the other outcomes was present after correcting for alpha inflation. When assessing the effect of age and education, education was significantly related to average reaction time and percent of omission errors. No significant effect of age was apparent. Findings suggest cognitive function, specifically sustained attention measured with a laboratory-based measure, may be associated with safe driving behavior.

Continuous performance task in ADHD: Is reaction time variability a key measure?

ObjectiveTo compare the use of the Continuous Performance Task (CPT) reaction time variability (intraindividual variability or standard deviation of reaction time), as a measure of vigilance in attention-deficit hyperactivity disorder (ADHD), and stimulant medication response, utilizing a simple CPT X-task vs an A-X-task.MethodComparative analyses of two separate X-task vs A-X-task data sets, and subgroup analyses of performance on and off medication were conducted.ResultsThe CPT X-task reaction time variability had a direct relationship to ADHD clinician severity ratings, unlike the CPT A-X-task. Variability in X-task performance was reduced by medication compared with the children’s unmedicated performance, but this effect did not reach significance. When the coefficient of variation was applied, severity measures and medication response were significant for the X-task, but not for the A-X-task.ConclusionThe CPT-X-task is a useful clinical screening test for ADHD and medication response. In particular, reaction time variability is related to default mode interference. The A-X-task is less useful in this regard.

Effects of Methylphenidate on Reaction Time in Children with Attention Deficit / Hyperactivity Disorder.

Attention-deficit/hyperactivity disorder (ADHD) is associated with a broad range of neuropsychological impairments that are attenuated with methylphenidate (MPH) treatment. The aim of this study was to determine how MPH effects attentional functioning in terms of reaction time (RT) in ADHD. Eighteen pre-medicated ADHD children (7 to 12 years old) and eighteen gender matched normal controls (7 to 12 years old) were included in the study. Participants performed an auditory attention task and the RT of participants to each target response was calculated automatically. The same test was repeated 3 months after OROS-MPH administration for ADHD group. RT, RT standard deviation (RTSD), and response errors (omission and commission errors) were compared between control and pre-MPH ADHD groups, and between Pre-MPH and post-MPH ADHD groups. Relative to control subjects, significantly longer RTs, higher RTSD and more errors of omission were observed in unmedicated ADHD children during auditory attention task. Analyses revealed significant effects of medication across all measures except commission errors. After treatment RTs were faster, RTSD values were lower, and errors of omission were attenuated compared to pre-medication condition in ADHD group. There were no significant differences in terms of commission errors between groups. In this study it was observed that MPH reduced RTs to stimuli, attenuated omission errors during the task in ADHD group and after 3 months of treatment ADHD children showed similar patterns in RT as compared to controls. Results suggest that when treating ADHD, it might help clinicians to evaluate objective and non-invasive cognitive outcomes such as RT, RTSD and response errors to evaluate the effects of treatment.

The Negative Influence of Adiposity Extends to Intraindividual Variability in Cognitive Control Among Preadolescent Children.

ObjectiveTo investigate the relationship between adiposity and cognition using mean accuracy, mean reaction time, and intraindividual variability (IIV) among preadolescents.MethodsChildren 7–9 years old (N=233, 133 females) underwent dual-energy x-ray absorptiometry and a VO2peak test to assess whole-body adiposity and aerobic fitness relative to fat-free mass (VO2FF), respectively. Attentional inhibition was assessed using a modified flanker task. IIV was assessed as standard deviation (SDRT) and coefficient of variation (CVRT) of response time. Hierarchical linear regression analyses were performed to examine the relationships between adiposity and cognitive measures following adjustment of significant demographic factors, intelligence quotient, and VO2FF.ResultsWhole-body adiposity was negatively related to congruent trial mean accuracy and reaction time and to CVRT in both the congruent and incongruent trials. Differences in cognitive function across weight status were selectively evident for measures of IIV such that children with overweight/obesity (≥85th BMI-for-age percentile) exhibited higher CVRT for both the congruent and incongruent trials.ConclusionThis work provides additional evidence linking childhood obesity to poorer cognitive function and includes novel data extending the negative influence of adiposity to measures of intraindividual response variability in cognitive control, even after accounting for intellectual abilities, aerobic fitness and demographic factors.

Methylphenidate, cognition, and epilepsy: A double-blind, placebo-controlled, single-dose study.

To evaluate the potential efficacy of immediate-release methylphenidate (MPH) for treating cognitive deficits in epilepsy. This was a double-blind, randomized, single-dose, 3-period crossover study in patients with epilepsy and chronic cognitive complaints comparing the effects of placebo and MPH 10 and 20 mg given 1 week apart. Cognitive outcome was evaluated on the basis of an omnibus z score calculated from performance on the Conners Continuous Performance Test 3 (ability to discriminate between target and nontarget stimuli [d'] and hit reaction time standard deviation), Symbol-Digit Modalities Test, and Medical College of Georgia Paragraph Memory Test. Adverse events and seizure frequency were monitored. An open-label follow-up is reported elsewhere. Thirty-five adult patients with epilepsy participated, of whom 31 finished. Demographics included the following: mean age = 35.3 years (range 20-62 years), 13 men and 18 women, and baseline seizure frequency of 2.8 per month. Epilepsy types were focal (n = 24), generalized (n = 6), or unclassified (n = 1). Mean epilepsy duration was 12.5 years. A statistically significant performance benefit was present at both 10-mg (p = 0.030) and 20-mg (p = 0.034) MPH doses. No seizures were associated with either MPH dose. Adverse effects leading to withdrawal included cognitive "fogginess" (n = 1 on 20 mg), anxiety/agitation (n = 1 on 10 mg), and tachycardia (n = 1). One participant was lost to follow-up after one 20-mg dose without side effect. This single-dose study suggests that MPH may be effective in ameliorating some cognitive deficits in patients with epilepsy. Additional studies are required. NCT02178995. This study provides Class II evidence that single doses of MPH improve cognitive performance on some measures of attention and processing speed in patients with epilepsy and cognitive complaints.

Physical attraction to reliable, low variability nervous systems: Reaction time variability predicts attractiveness

The human face cues a range of important fitness information, which guides mate selection towards desirable others. Given humans’ high investment in the central nervous system (CNS), cues to CNS function should be especially important in social selection. We tested if facial attractiveness preferences are sensitive to the reliability of human nervous system function. Several decades of research suggest an operational measure for CNS reliability is reaction time variability, which is measured by standard deviation of reaction times across trials. Across two experiments, we show that low reaction time variability is associated with facial attractiveness. Moreover, variability in performance made a unique contribution to attractiveness judgements above and beyond both physical health and sex-typicality judgements, which have previously been associated with perceptions of attractiveness. In a third experiment, we empirically estimated the distribution of attractiveness preferences expected by chance and show that the size and direction of our results in Experiments 1 and 2 are statistically unlikely without reference to reaction time variability. We conclude that an operating characteristic of the human nervous system, reliability of information processing, is signalled to others through facial appearance.

Response time variability under slow and fast‐incentive conditions in children with ASD, ADHD and ASD+ADHD

BackgroundAttention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD) show significant behavioural and genetic overlap. Both ADHD and ASD are characterised by poor performance on a range of cognitive tasks. In particular, increased response time variability (RTV) is a promising indicator of risk for both ADHD and ASD. However, it is not clear whether different indices of RTV and changes to RTV according to task conditions are able to discriminate between the two disorders.MethodsChildren with ASD (n = 19), ADHD (n = 18), ASD + ADHD (n = 29) and typically developing controls (TDC; n = 26) performed a four‐choice RT task with slow‐baseline and fast‐incentive conditions. Performance was characterised by mean RT (MRT), standard deviation of RT (SD‐RT), coefficient of variation (CV) and ex‐Gaussian distribution measures of Mu, Sigma and Tau.ResultsIn the slow‐baseline condition, categorical diagnoses and trait measures converged to indicate that children with ADHD‐only and ASD + ADHD demonstrated increased MRT, SD‐RT, CV and Tau compared to TDC and ASD‐only. Importantly, greater improvement in MRT, SD‐RT and Tau was demonstrated in ADHD and ASD + ADHD from slow‐baseline to fast‐incentive conditions compared to TDC and ASD‐only.ConclusionsSlower and more variable RTs are markers of ADHD compared to ASD and typically developing controls during slow and less rewarding conditions. Energetic factors and rewards improve task performance to a greater extent in children with ADHD compared to children with ASD. These findings suggest that RTV can be distinguished in ASD, ADHD and ASD + ADHD based on the indices of variability used and the conditions in which they are elicited. Further work identifying neural processes underlying increased RTV is warranted, in order to elucidate disorder‐specific and disorder‐convergent aetiological pathways.

Effects of Psychiatric Symptoms on Attention in North Korean Refugees.

ObjectiveWe investigated the performance of North Korean refugees on attention tasks, and the relationship between that performance and psychiatric symptoms.MethodsSustained and divided attention was assessed using the computerized Comprehensive Attention Test in North Korean refugees and in South Koreans. All participants also completed the Beck Depression Inventory, the Beck Anxiety Inventory, the Impact of Event Scale-Revised and the Dissociative Experiences Scale-II (DES-II).ResultsThe North Korean refugees showed slower reaction times (RTs) on the visual sustained attention task compared to the South Koreans after controlling for age and sex. North Korean refugees had a greater number of omission errors (OEs) on the divided attention task and a higher standard deviation (SD) of RT. Total DES-II scores of the North Korean refugees were associated with the number of OEs and the SD of RT on the sustained attention task, and with the number of OEs on the divided attention task.ConclusionNorth Korean refugees showed poorer performance on computerized attention tasks. In addition, attention deficit among North Korean refugees was associated with their dissociative experiences. Our results suggest that refugees may have attention deficits, which may be related to their psychiatric symptoms, particularly dissociation.

PP11.5 – 2670: Combined analysis of volumetric- and DT-MRI in children with ADHD: Correlations between task performances and MRI measurements in subcortical structures

Objective To assess differences between children with attentiondeficit/hyperactivity disorder (ADHD) and typically developing children (TDC) through the correlation between task performances and MRI measurements in the basal ganglia and thalamus. Methods Eleven TDC and 11 children who met diagnostic critaria for ADHD, combined type medication-free, underwent structural-MRI and diffusion tensor imaging (DTI). Volumetric and mean diffusivity (MD) measurements of the striatum (caudate and putamen), pallidum and thalamus were determined. Individuals reaction times (RTs) performances were assessed using a flanker task. The relationships between the individuals scores of mean and standard deviation of RTs (MRT and ISD, respectively) with the volumetric and MD measurements were assessed using the Spearman's correlation analysis. Results We did not found any significant correlation between the standard deviation of RTs with the volumetric and MD measurements neither for children with ADHD nor for controls. However, significant correlations were found between the MRTs and MD measurements increase in mean of RTs were linked (or significantly correlated with) to increase in MD measurements, in the caudate bilaterally, only for the group of children with ADHD (left Spearman's correlation coefficient (r) = 0.69, right r=0.62, P Conclusion The results substantiate support the hypothesis that dysfunctions in the striatal system may affect certain executive processes in children with ADHD. Despite of the relative low samples of children, these results may aid to extent our understanding of the microstructural substrates of ADHD.

Effects of task repetition on event-related potentials in somatosensory Go/No-go paradigm

We investigated the effects of task repetition on the N140 and P300 components of event-related potentials (ERPs) in somatosensory Go/No-go paradigms. A Go or No-go stimulus was presented to the second or fifth digit of the left hand, respectively, at the same probability, and subjects had to respond by pushing a button with their right thumb as quickly as possible only after the presentation of a Go stimulus. The condition comprised seven sessions of recordings, and subjects were allowed to relax for five minutes after one session. The behavioral data for the reaction time (RT), standard deviation of RT, and error rates showed the absence of an effect by task repetition. In ERP waveforms, the amplitudes of N140 and P300 decreased with task repetition, and the latency of P300 was delayed by task repetition. There was no significant effect of task repetition on the peak latency of N140.Changes in amplitude and latency values in N140 and P300 during Go/No-go paradigms reflected changes in the neural activation of response execution and inhibition processing with task repetition.

Cognitive performance and BMI in childhood: Shared genetic influences between reaction time but not response inhibition.

The aim of this work is to understand whether shared genetic influences can explain the association between obesity and cognitive performance, including slower and more variable reaction times (RTs) and worse response inhibition. RT on a four-choice RT task and the go/no-go task, and commission errors on the go/no-go task for 1,312 twins ages 7-10 years were measured. BMI was measured at 9-12 years. Biometric twin models were run to give an estimate of the genetic correlation (rG ) between body mass index (BMI) and three cognitive measures: mean RT (MRT), RT variability (RTV; the standard deviation of RTs), and commission errors (a measure of response inhibition). Genetic correlations indicated that 20%-30% of the genes underlying BMI were shared with both RT measures. However, only small phenotypic correlations between MRT and RTV with later BMI (rPh = ∼0.1) were observed. Commission errors were unassociated with later BMI (rPh = -0.03, ns). Our results are the first to demonstrate significant shared genetic effects between RT performance and BMI. Our findings add biological support to the notion that obesity is associated with slower and more variable RTs. However, our results also emphasize the small nature of the association, which may explain previous negative findings.

The relationship of moderate-to-vigorous physical activity to cognitive processing in adolescents: findings from the ALSPAC birth cohort.

The aim of this study was to assess the relations of daily moderate-to-vigorous physical activity (MVPA) to cognitive functions in 15-year-old adolescents from the Avon Longitudinal Study of Parents and Children while controlling for aerobic fitness. A sub-sample of 667 adolescents (M(age) = 15.4 ± 0.16 years; 55% females) who provided valid data on variables of interest, were used in the analyses. MVPA was objectively assessed using an Actigraph GT1M accelerometer and aerobic fitness was expressed as physical work capacity at the heart rate of 170 beats per minute from a cycle ergometer test. A computerized stop-signal task was used to measure mean reaction time (RT) and standard deviation of RT, as indicators of cognitive processing speed and variability during an attention and inhibitory control task. MVPA was not significantly related to cognitive processing speed or variability of cognitive performance in hierarchical linear regression models. In simple regression models, aerobic fitness was negatively related to mean RT on the simple go condition. Our results suggest that aerobic fitness, but not MVPA, was associated with cognitive processing speed under less cognitively demanding task conditions. The results thus indicate a potential global effect of aerobic fitness on cognitive functions in adolescents but this may differ depending on the specific task characteristics.

Reaction Time Variability Associated with Reading Skills in Poor Readers with ADHD

Linkages between neuropsychological functioning (i.e., response inhibition, processing speed, reaction time variability) and word reading have been documented among children with attention-deficit/hyperactivity disorder (ADHD) and children with Reading Disorders. However, associations between neuropsychological functioning and other aspects of reading (i.e., fluency, comprehension) have not been well-documented among children with comorbid ADHD and Reading Disorder. Children with ADHD and poor word reading (i.e., ≤25th percentile) completed a stop signal task (SST) and tests of word reading, reading fluency, and reading comprehension. Multivariate multiple regression was conducted predicting the reading skills from SST variables [i.e., mean reaction time (MRT), reaction time standard deviation (SDRT), and stop signal reaction time (SSRT)]. SDRT predicted word reading, reading fluency, and reading comprehension. MRT and SSRT were not associated with any reading skill. After including word reading in models predicting reading fluency and reading comprehension, the effects of SDRT were minimized. Reaction time variability (i.e., SDRT) reflects impairments in information processing and failure to maintain executive control. The pattern of results from this study suggest SDRT exerts its effects on reading fluency and reading comprehension through its effect on word reading (i.e., decoding) and that this relation may be related to observed deficits in higher-level elements of reading.

Modulation of Attention-Deficit/Hyperactivity Disorder Symptoms by Short- and Long-Acting Methylphenidate over the Course of a Day

The purpose of this study was to investigate whether a long-acting methylphenidate formulation (MPH-ret) is as effective as two doses of immediate-release methylphenidate (MPH-IR) in reducing attention-deficit/hyperactivity disorder (ADHD) symptoms including inattention, impulsivity, and hyperactivity during the course of the day. Two groups of children (n=18 each) with ADHD aged between 8 and 12 years completed a continuous performance test in combination with a motion-tracking system four times a day within 8 hours. Inattention (standard deviation of reaction time), impulsivity (commission error rate), and hyperactivity (path length of the headband) were simultaneously measured. We included a control group (n=20) to rule out circadian fluctuations of attentional performance and motor activity. We observed a postlunch dip in attentional performance and an increasing trend of motor activity throughout the day whereas impulsivity remained stable in controls. The MPH-ret and MPH-IR groups had comparable treatment effects on measures of hyperactivity and inattention and normalized participant performance to control levels. In contrast, MPH-IR seems to have an advantage over MPH-ret in impulsivity treatments. Thus, our data suggest that it is crucial to assess the different domains of ADHD symptoms precisely over the course of a day to determine the optimal titration and stimulant formulation for a person with ADHD.

ADHD Preschoolers With and Without ODD

Objective: To examine the impact of reinforcement on reaction time (RT) and RT variability (RT standard deviation [RTSD]) in preschoolers with ADHD with and without oppositional defiant disorder (ODD), and a typically developing (TD) comparison group. Method: Participants were administered a computerized task consisting of two conditions: simple RT (SRT) and reinforced SRT (SRTr). Data were analyzed using two-way (Group × Condition) mixed ANOVAs and followed-up using pairwise comparisons. Results: RTs were significantly shorter and less variable during the SRTr than the SRT condition. A significant Group x Condition interaction was observed for RTSD (F= 3.38, p < .05); post hoc analyses indicated that the RTSD of the ADHD + ODD group was significantly more variable than that of the TD group during the SRT condition (F = 4.81, p < .05). However, their RTSD was statistically indistinguishable from the other groups during the SRTr condition. Conclusion: Preschoolers who are oppositional/defiant and hyperactive are the most responsive to feedback/reward.

Information processing speed, neural efficiency, and working memory performance in multiple sclerosis: Differential relationships with structural magnetic resonance imaging

Multiple sclerosis (MS), a central nervous system (CNS) neurodegenerative disorder, involves lesions of both white and gray matter and reported cognitive impairments that include processing speed (PS), executive function, and working memory (WM). This study closely examined the specifics of these cognitive deficits and their relationship to structural brain damage. A visual n-back task with 3 WM load conditions was used to assess WM performance (task accuracy), PS (reaction time, RT), and a novel measure of processing efficiency (standard deviation of RT, RTSD) in MS patients and controls. These behavioral measures were related to quantitative magnetic resonance imaging (MRI) measures of white and gray matter integrity. Even when MS patients performed as well as controls, as seen for low WM load (0-back), they responded more slowly and were less efficient in their speed of responding. Accuracy findings indicated that the correct match trials were superior to correct nonmatch trials at differentiating MS patients from controls. Further, decreased accuracy during the highest WM load condition was associated with global damage that included both gray and white matter atrophy, while slowed PS and particularly processing inefficiency were associated primarily with white matter atrophy in MS. Importantly, relationships between PS, processing efficiency, performance accuracy, and structural MRI measures were seen only during the highest WM load condition, the condition that required the most executive control. These findings suggest that the MRI/behavioral relationships that were present exclusively during the 2-back condition may reflect connectivity involving frontal cortical systems, the site for executive control.