Visuospatial Working Memory Performance Research Articles

The Impact of Stimulant Medication on the Relation Between Working Memory and Activity Level in ADHD.

There is a positive association between heightened activity levels and improved working memory performance (WM) in individuals with Attention-Deficit/Hyperactivity Disorder (ADHD). Recent research suggests that stimulant medications may have a simultaneous positive impact on WM and motor skills. Yet, it is unclear the specific connection between movement, WM, and stimulant use. We examined how visuospatial (VS) and phonological (PH) WM performance varied with children's stimulant medication usage and naturally occurring activity level. In a repeated measures design, children with ADHD (n = 43; 7-12years old) completed WM tasks while wearing actigraphy watches to monitor activity level on and off stimulant medication. Significant large sized main effects were observed for medication condition on PH (p < .05, ηp2 = .14) and VS (p < .001, ηp2 = .30) WM. Activity level also had significant medium sized main effects on PH (p < .01, ηp2 = .09) and VS (p < .005, ηp2 = .10) WM. There was a significant medium sized interaction for VS WM (p < .005, ηp2 = .11), indicating that the effect of medication on performance was greatest in the highest activity level category. The findings suggest that a combination of stimulant medication and an "optimal" level of movement may be most effective for improving VS WM.

Preclinical Brain Network Abnormalities in Patients with Subjective Cognitive Decline.

Alzheimer's disease (AD) is the most common form of dementia worldwide. Currently there are no disease modifying treatments available. Detecting subjects with increased risk to develop dementia is essential for future clinical trials. Subjective cognitive decline (SCD) is a condition defining individuals who perceive a decrease in their own cognitive functioning in the absence of any detectable deficit on neuropsychological testing. SCD individuals show AD-related biomarkers abnormalities in cerebrospinal fluid. The aim of the present study was to assess brain functional connectivity (FC) changes in SCD individuals. 23 SCD and 33 healthy subjects (HS) underwent an extensive neuropsychological assessment and 3T-MRI scanning including a T1-w volume and resting-state fMRI (RS-fMRI) to assess brain atrophy and brain FC. No between-group differences in grey matter volumes were detected. SCD subjects compared to HS showed both increased and decreased FC in the executive and parietal networks. Associations between cognitive measures, mainly assessing working memory, and FC within brain networks were found both in SCD and HS separately. SCD individuals showed FC abnormalities in networks involving fronto-parietal areas that may account for their lower visuo-spatial working memory performances. Dysfunctions in executive-frontal networks may be responsible for the cognitive decline subjectively experienced by SCD individuals despite the normal scores observed by formal neuropsychological assessment. The present study contributes to consider SCD individuals in an early AD stage with an increased risk of developing the disease in the long term.

Exposure to natural environments consistently improves visuospatial working memory performance

Exposure to natural environments has shown to have a positive influence on executive mental functioning. In the present study, we investigated whether these nature-related cognitive benefits can extend to visuospatial working memory (WM), a cognitive function relatively underexplored on this topic. Participants performed a Change Localization task in three different experiments. On each trial, a sample array containing four colored shapes was briefly presented (100 ms) and followed, after a short delay (900 ms), by a similar test array that changed the color of one of the items, which participants had to identify. They completed this visuospatial WM task before and after exposure to images of either natural landscapes or urban settings, with both types being presented across two different sessions. Participants’ WM performance systematically improved because of exposure to natural, but not to urban images, even when the aesthetic preference for natural and urban stimuli was controlled for.

Transcranial alternating current stimulation over multiple brain areas with non-zero phase delays other than 180 degrees modulates visuospatial working memory performance

While zero-phase lag synchronization between multiple brain regions has been widely observed, relatively recent reports indicate that systematic phase delays between cortical regions reflect the direction of communications between cortical regions. For example, it has been suggested that a non-zero phase delay of electroencephalography (EEG) signals at the gamma frequency band between the bilateral parietal areas may reflect the direction of communication between these areas. We hypothesized that the direction of communication between distant brain areas might be modulated by multi-site transcranial alternating current stimulation (tACS) with specific phase delays other than 0° and 180°. In this study, a new noninvasive brain stimulation (NIBS) method called multi-site multi-phase tACS (msmp-tACS) was proposed. The efficacy of the proposed method was tested in a case study using a visuospatial working memory (VWM) paradigm in which the optimal stimulation conditions including amplitudes and phases of multiple scalp electrodes were determined using finite element analysis adopting phasor representation. msmp-tACS was applied over the bilateral intraparietal sulci (IPS) and showed that 80 Hz tACS with the phase for the right IPS leading that for the left IPS by 90° (= 3.125 ms) partialized VWM performance toward the right visual hemifield. The three stimulation conditions were synchronized, RL, and LR, which refers to stimulation condition with no phase lag, stimulation phase of right IPS (rIPS) leading left IPS (lIPS) by 90° and the stimulation of lIPS leading rIPS by 90°, respectively. The lateralization of VWM significantly shifted towards right visual hemifield under the RL condition compared to the synchronized and LR conditions. The shift in VWM was the result of the stimulation affecting both left and right visual hemifield trials to certain degrees, rather than significantly increasing or decreasing VWM capacity of a specific visual hemifield. Altered brain dynamics caused by msmp-tACS partialized VWM performance, likely due to modulation of effective connectivity between the rIPS and lIPS. Our results suggest that msmp-tACS is a promising NBS method that can effectively modulate cortical networks that cannot be readily modulated with conventional multi-site stimulation methods.

Modulation of visuospatial working memory performance using dual-site transcranial current stimulation of bilateral intraparietal sulci with high-gamma alternating currents with different phases

Modulation of visuospatial working memory performance using dual-site transcranial current stimulation of bilateral intraparietal sulci with high-gamma alternating currents with different phases

Do emotions evoked by music modulate visuospatial working memory capacity? A physiological study

Previous studies have shown that emotions evoked through music can have transient effects on cognitive performance. Considering the importance of working memory (WM) in the processing of new information, in this study, we investigated the impact of positive and negative emotions evoked through music on visuospatial WM performance using a within-subjects design. Moreover, we concomitantly recorded the participants’ physiological responses during listening to musical stimuli. Seventy-eight participants were allocated to counterbalanced positive, negative, and neutral emotional inductions through music (EIM) followed by an adaptive visuospatial WM task. Results revealed that participants’ visuospatial WM performance was increased after positive EIM compared with negative and neutral EIMs transiently. We also observed increased skin conductance levels during positive EIM compared with baseline and a lower heart rate throughout positive EIM than the other conditions. Overall, these findings suggest that music evoking positive emotions can boost visuospatial WM performance. This is the first study to explore cognitive performance after EIM and physiological responses to musical stimuli simultaneously, which may have important practical implications since we engage in cognitively demanding activities after listening to music that could evoke happy or sad emotions.

Attentional Orienting in Working Memory in Children with ADHD

ABSTRACT Children with attentional-deficit/hyperactivity disorder (ADHD) have impairments in working memory (WM) functioning. Impaired orienting of visual attention during encoding and/or maintenance is hypothesized as the cause of poor performance in visuospatial WM in 10-to-16-year-olds. We used a color-recognition task with valid location cues before encoding (pre-cues) and during maintenance (retro-cues). If ADHD children have an orienting deficit during these processing stages, they should not benefit from the cues. We observed strong pre- and retro-cueing benefits both for ADHD and typically developing controls, with no differences between the groups. This strengthens findings showing that ADHD is not characterized by deficits in orienting attention and provides evidence of retro-cue benefits in this population.

Visuo-spatial working memory for objects and configurations in natural scenes in university students with ADHD

ABSTRACT Adults with ADHD typically show reduced performance in visuo-spatial working memory (VSWM) tasks. These limitations have been observed mainly in tasks probing VSWM for low-level visual information. The current study investigated whether these limitations extended to memory for real-world objects, and memory for the spatial context in which they were presented. Sixty-four university students with and without ADHD memorised the form of real-world objects embedded in natural scenes. Following a short delay, participants were probed on a single object in the scene that could change in token or orientation, and that could appear within the original scene or in isolation. Consistent with previous studies, memory for the individual objects was impaired in the ADHD group relative to the control group, demonstrating that this deficit extends to complex real-world objects. Nevertheless, participants in the ADHD group benefited from the reinstatement of the scene during retrieval to the same extent as participants in the control group. This finding suggests that participants in the ADHD group formed and maintained a representation of the spatial context of the scene that aided memory retrieval. Overall, the results support an emerging view that VSWM operates on multiple, possibly independent, representations at different hierarchal levels.

Enhancing Visuospatial Working Memory Performance Using Intermittent Theta-Burst Stimulation Over the Right Dorsolateral Prefrontal Cortex.

Noninvasive brain stimulation provides a promising approach for the treatment of neuropsychiatric conditions. Despite the increasing research on the facilitatory effects of this kind of stimulation on the cognitive processes, the majority of the studies have used the standard stimulation approaches such as the transcranial direct current stimulation and the conventional repetitive transcranial magnetic stimulation (rTMS) which seem to be limited in robustness and the duration of the transient effects. However, a recent specialized type of rTMS, theta-burst stimulation (TBS), patterned to mimic the natural cross-frequency coupling of the human brain, may induce robust and longer-lasting effects on cortical activity. Here, we aimed to investigate the effects of the intermittent TBS (iTBS), a facilitatory form of TBS, over the right DLPFC (rDLPFC), a brain area implicated in higher-order cognitive processes, on visuospatial working memory (VSWM) performance. Therefore, iTBS was applied over either the rDLPFC or the vertex of 24 healthy participants, in two separate sessions. We assessed VSWM performance using 2-back and 4-back visuospatial tasks before iTBS (at the baseline (BL), and after the iTBS. Our results indicate that the iTBS over the rDLPFC significantly enhanced VSWM performance in the 2-back task, as measured by the discriminability index and the reaction time. However, the 4-back task performance was not significantly modulated by iTBS. These findings demonstrate that the rDLPFC plays a critical role in VSWM and that iTBS is a safe and effective approach for investigating the causal role of the specific brain areas.

Visuospatial working memory of children and adults born very preterm and/or very low birth weight.

This paper examines the visuospatial working memory (WM) performance of children and adults born very preterm (VPT) and/or very low birth weight (VLBW) relative to their full-term (FT)-born peers. Of interest was the nature and severity of observed impairments, as well associations with educational/occupational functioning at each age point. Participants were drawn from two prospective cohort studies: (1) a regional cohort of 110 VPT (<32 weeks' gestation and <1500 g) and 113 FT born children assessed at age 12 years; (2) a national cohort of 229 VLBW (<1500 g) and 100 FT born adults assessed at age 28 years. Visuospatial WM was assessed using a four-span/difficulty-level computerized task. Both children and adults born VPT/VLBW had poorer visuospatial WM than FT controls, with their performance less accurate, slower (correct trials), and less efficient with increasing task difficulty (Cohen's d = 0.27-0.51; p < 0.05). Adults had better visuospatial WM than children, but between-group differences were highly similar across ages, before and after adjustment for confounding social background and individual factors. Poorer WM was associated with lower levels of educational and occupational/socioeconomic achievement. Visuospatial WM difficulties persist into adulthood raising concerns for the longer-term cognitive and adaptive functioning of VPT survivors. Both children and adults born very preterm have poorer visuospatial working memory than their term-born peers. They are less accurate, take longer to respond correctly and are less efficient, with test performance declining with increasing cognitive demand. Similar differences in visuospatial working memory are observed between VPT/VLBW and full-term individuals during both childhood and adulthood, with these differences remaining even after covariate adjustment. Individuals with poorer visuospatial working memory have lower levels of educational achievement and occupational/socioeconomic success. Visuospatial working memory difficulties persist into adulthood and appear tocontinue to impact everyday functioning and life-course opportunities.

Electrophysiological Brain Changes Associated With Cognitive Improvement in a Pediatric Attention Deficit Hyperactivity Disorder Digital Artificial Intelligence-Driven Intervention: Randomized Controlled Trial.

BackgroundCognitive stimulation therapy appears to show promising results in the rehabilitation of impaired cognitive processes in attention deficit hyperactivity disorder.ObjectiveEncouraged by this evidence and the ever-increasing use of technology and artificial intelligence for therapeutic purposes, we examined whether cognitive stimulation therapy implemented on a mobile device and controlled by an artificial intelligence engine can be effective in the neurocognitive rehabilitation of these patients.MethodsIn this randomized study, 29 child participants (25 males) underwent training with a smart, digital, cognitive stimulation program (KAD_SCL_01) or with 3 commercial video games for 12 weeks, 3 days a week, 15 minutes a day. Participants completed a neuropsychological assessment and a preintervention and postintervention magnetoencephalography study in a resting state with their eyes closed. In addition, information on clinical symptoms was collected from the child´s legal guardians.ResultsIn line with our main hypothesis, we found evidence that smart, digital, cognitive treatment results in improvements in inhibitory control performance. Improvements were also found in visuospatial working memory performance and in the cognitive flexibility, working memory, and behavior and general executive functioning behavioral clinical indexes in this group of participants. Finally, the improvements found in inhibitory control were related to increases in alpha-band power in all participants in the posterior regions, including 2 default mode network regions of the interest: the bilateral precuneus and the bilateral posterior cingulate cortex. However, only the participants who underwent cognitive stimulation intervention (KAD_SCL_01) showed a significant increase in this relationship.ConclusionsThe results seem to indicate that smart, digital treatment can be effective in the inhibitory control and visuospatial working memory rehabilitation in patients with attention deficit hyperactivity disorder. Furthermore, the relation of the inhibitory control with alpha-band power changes could mean that these changes are a product of plasticity mechanisms or changes in the neuromodulatory dynamics.Trial RegistrationISRCTN Registry ISRCTN71041318; https://www.isrctn.com/ISRCTN71041318

Disruption in Surface-Based Functional Connectivity in the Right Posterior Hippocampal CA3 Subfield: A Probable Neural Basis of Visuospatial Working Memory Impairment in Patients With Right Temporal Lobe Epilepsy.

Visuospatial working memory (VSWM) impairment is common in patients with right temporal lobe epilepsy (rTLE). The posterior hippocampus is critical for spatial memory, but the contributions of the different subfields to VSWM deficits remain unclear. Forty-six rTLE patients and 42 healthy controls (HCs) were recruited. Resting-state fMRI (rsfMRI) and structural MRI scans were administered, followed by a VSWM_Nback test. The right posterior hippocampus was automatically segmented, and the surface-based functional connectivity (SBFC) of the subiculum (Sub), CA1, CA3, dentate gyrus (DG), hippocampal tail, and right entorhinal cortex (EC) were compared between groups. Correlation analysis was performed between the altered SBFC and VSWM_Nback scores for rTLE patients. The results showed that rTLE patients underperformed in the VSWM_Nback test, with longer mean reaction time of accurate response (ACCmeanRT) in 0back and 2back condition, lower hit rate (HR) and higher false alarm rate (FAR) in 2back condition. Compared with HCs, the rCA3 in the rTLE group exhibited decreased SBFC with inferior parietal cortex (IPC), temporal lateral cortex (TLC), and posterior visual cortex (PVC) in the right hemisphere as well as the bilateral dorsolateral prefrontal cortex (DLPFC). The SBFC of the rEC and right anterior cingulate cortex (rACC) increased in the rTLE group. Within the rTLE group, the decreased SBFC of the rCA3-rIPC and rCA3-rLTC were correlated with worse VSWM performance. Therefore, the decreased SBFC of the rCA3-rIPC and rCA3-rLTC might be the critical aberrant FC pattern reflecting VSWM impairment in rTLE patients. The mechanism might involve functional disruption between the core subsystem and the medial temporal subsystem of the default mode network (DMN).

Does Gender Difference Play a Significant Role in Verbal and Visuospatial Working Memory Performance?

The present study investigates gender differences in working memory performance, both verbal and visuospatial working memory performance. Quasi-experimental research was conducted individually on 32 undergraduates at a public university in Malaysia, using a reading span task and rotation span task. The performance was based on the total number of correct recalled and the total time taken. Results showed a significant gender difference in the verbal and visuospatial working memory performance. The observation was based on the total time taken, in which males performed more rapidly than females in both tasks. In terms of accuracy, female participants recalled better than their male counterparts in the verbal task, which is consistent with numerous past studies. However, no gender difference was identified in the visuospatial task performance, based on the total number of correct recalled. The study also found that male participants did not show an advantage in visuospatial abilities, contradicting findings by past studies.

Errors in visuospatial working memory across space and time

Visuospatial working memory (VSWM) involves cortical regions along the dorsal visual pathway, which are topographically organized with respect to the visual space. However, it remains unclear how such functional organization may constrain VSWM behavior across space and time. Here, we systematically mapped VSWM performance across the 2-dimensional (2D) space in various retention intervals in human subjects using the memory-guided and visually guided saccade tasks in two experiments. Relative to visually guided saccades, memory-guided saccades showed significant increases in unsystematic errors, or response variability, with increasing target eccentricity (3°–13° of visual angle). Unsystematic errors also increased with increasing delay (1.5–3 s, Experiment 1; 0.5–5 s, Experiment 2), while there was little or no interaction between delay and eccentricity. Continuous bump attractor modeling suggested neurophysiological and functional organization factors in the increasing unsystematic errors in VSWM across space and time. These findings indicate that: (1) VSWM representation may be limited by the functional topology of the visual pathway for the 2D space; (2) Unsystematic errors may reflect accumulated noise from memory maintenance while systematic errors may originate from non-mnemonic processes such as noisy sensorimotor transformation; (3) There may be independent mechanisms supporting the spatial and temporal processing of VSWM.

A decision-neuroscientific intervention to improve cognitive recovery after stroke.

Functional recovery after stroke is dose-dependent on the amount of rehabilitative training. However, rehabilitative training is subject to motivational hurdles. Decision neuroscience formalizes drivers and dampers of behaviour and provides strategies for tipping motivational trade-offs and behaviour change. Here, we used one such strategy, upfront voluntary choice restriction ('precommitment'), and tested if it can increase the amount of self-directed rehabilitative training in severely impaired stroke patients. In this randomized controlled study, stroke patients with working memory deficits (n = 83) were prescribed daily self-directed gamified cognitive training as an add-on to standard therapy during post-acute inpatient neurorehabilitation. Patients allocated to the precommitment intervention could choose to restrict competing options to self-directed training, specifically the possibility to meet visitors. This upfront choice restriction was opted for by all patients in the intervention group and highly effective. Patients in the precommitment group performed the prescribed self-directed gamified cognitive training twice as often as control group patients who were not offered precommitment [on 50% versus 21% of days, Pcorr = 0.004, d = 0.87, 95% confidence interval (CI95%) = 0.31 to 1.42], and, as a consequence, reached a 3-fold higher total training dose (90.21 versus 33.60 min, Pcorr = 0.004, d = 0.83, CI95% = 0.27 to 1.38). Moreover, add-on self-directed cognitive training was associated with stronger improvements in visuospatial and verbal working memory performance (Pcorr = 0.002, d = 0.72 and Pcorr = 0.036, d = 0.62). Our neuroscientific decision add-on intervention strongly increased the amount of effective cognitive training performed by severely impaired stroke patients. These results warrant a full clinical trial to link decision-based neuroscientific interventions directly with clinical outcome.

The Visuo-Spatial Abilities Diagnosis (VSAD) test: Evaluating the potential cognitive difficulties of children with vestibular impairment through a new tablet-based computerized test battery.

Recent data collected on adult patients with vestibular loss (VL) tend to demonstrate possible cognitive impairments in visuospatial working memory, mental rotation, selective attention, and space orientation. However, the neuropsychological profile of children with VL remains largely under-investigated in the scientific literature. Although previous research has shown that children with VL may experience some degree of delayed motor development, it is not yet clear if VL could also lead to specific delayed cognitive development. In this study, we will present the development and validation of a new tablet-based computerized test battery (VSAD) that evaluates visuospatial working memory, mental rotation, selective attention, and space orientation abilities. Thirteen children with VL and 54 average-age matched healthy children performed the VSAD and classical paper-and-pencil neuropsychological tasks twice within a 1-month interval. Our results demonstrated a good concurrent validity with strong correlations between the visuospatial working memory, mental rotation, and space orientation tests of the VSAD and classical tasks. Test-retest reliability was also supported through good intra-class coefficients. However, the test of selective attention showed no concurrent validity with the matched classical task. The discriminant validity of the VSAD was partially supported for visuospatial working memory and mental rotation performance accuracy. The VSAD shows good concurrent validity and reliability for measuring visuospatial working memory, mental rotation, and space orientation in children with VL. Future studies are needed to extend discriminant validity with other populations.

Cognitive Mechanisms of Monolingual and Bilingual Children in Monoliterate Educational Settings: Evidence From Sentence Repetition.

Sentence repetition (SR) tasks have been extensively employed to assess bilingual children’s linguistic and cognitive resources. The present study examined whether monoliterate bilingual children differ from their monolingual (and monoliterate) peers in SR accuracy and cognitive tasks, and investigated links between vocabulary, updating, verbal and visuospatial working memory and SR performance in the same children. Participants were two groups of 35 children, 8–12 years of age: one group consisted of Albanian-Greek monoliterate bilingual children and the other of Greek monolingual children attending a monolingual-Greek educational setting. The findings demonstrate that the two groups performed similarly in the grammaticality scores of the SR. However, monolinguals outperformed the monoliterate bilinguals in SR accuracy, as well as in the visuospatial working memory and updating tasks. The findings did not indicate any bilingual advantage in cognitive performance. The results also demonstrate that updating and visuospatial working memory significantly predicted monolingual children’s SR accuracy scores, whereas Greek vocabulary predicted the performance of our monoliterate bilingual children in the same task. We attribute this outcome to the fact that monoliterate bilingual children do not rely on their fluid cognitive resources to perform the task, but instead rely on language proficiency (indicated by expressive vocabulary) while performing the SR.

The Working Memory as Predictor of Performance in Arithmetic of Brazilian Students

Abstract Working memory (WM) is a predictor of school learning. This study aimed to investigate the predictive power of verbal and non-verbal working memory (WM) on students’ performance in arithmetic. 126 children between 6 and 11 years old participated in the research. The instruments were: School Performance Test, Raven’s Colored Progressive Matrices, Corsi Block-tapping Test, and Digits Subtest. The results showed strong and positive correlations of school performance with fluid intelligence r = 0.64, with verbal WM and non-verbal WM, both with r = 0.51 (p &lt; 0.001). After multiple linear regression, it was found that the performance in visuospatial WM was a strong predictor for arithmetic, an effect not found for reading. The regression showed that WM explains 38% of the variance for arithmetic. It is concluded that WM has an expressive contribution to school performance, being more specific the contributions of visuospatial WM for arithmetic.

Development of visuospatial memory in preterm infants: A new paradigm to assess short-term and working memory

ABSTRACT Preterm infants have a higher risk of showing visuospatial memory impairment, the function that allows to encode and remember visual and spatial information. It has been studied in late childhood in preterm children. Studies on visuospatial memory throughout the first 2 years of life are still scarce. Behavior, temperament, and overall cognition could be altered in preterm children affecting memory performance. Therefore, the main aim of this study was to evaluate short-term and visuospatial working memory performance in a preterm sample followed longitudinally at 12, 15, 18, and 22 months (N = 15), and compare their performance with that of full-term children (N = 65). The secondary aim was to analyze the course of mnesic development in preterm infants and relate their memory performance to other cognitive abilities and behavioral tendencies. Assessment included previously published tasks and an experimental paradigm. Results showed that preterm children scored lower than full-term children on visuospatial short-term and working memory at 12 and 22 months of age, although these results varied depending on the memory test used. Preterm children’s memory results showed that these skills improve in this population between the first and second year of life. Finally, memory performance was directly associated with the level of cognitive development and the presence of proactive behaviors, while being inversely correlated with the presence of disruptive behaviors and a difficult temperamental style. These preliminary findings suggest that it is possible to detect visuospatial memory difficulties in the preterm population before the age of two.

Stereotype Threat Effect on a Simple Motor Task: An Investigation of the Visuo-Spatial Working Memory

ABSTRACT Purpose: Based on the Chalabaev et al. (2013) study showing that in a Stereotype Threat (ST) situation the velocity of force production in a simple motor task can be affected, this study aimed to replicate this result and tested the role of Visuo-Spatial Working Memory (VSWM) in the ST effect. Method: Twenty one female athletes performed maximum voluntary contractions of the knee extensor muscles on an isokinetic dynamometer (Biodex), under neutral, ST, and ST with mental imagery conditions. The Rate Force of Development (RFD), a velocity indicator, was measured under each condition. VSWM and avoidance-related processes were measured in at a separate time. Results: Data confirmed that the RFD decreased when the stereotype threat was introduced, but also that mental imagery of the movement in the pre-contraction stage prevented this effect. Moreover, in the ST condition avoidance-related processes did not affect the RFD. In contrast, higher VSWM performance was associated with higher RFD. Conclusion: These findings suggest that the ST effects on a simple motor task can be explained by an alteration of working memory which impairs movement preparatory processes in the pre-contraction stage.