Support for distinct subcomponents of spatial working memory: A double dissociation between spatial–simultaneous and spatial–sequential performance in unilateral neglect

The engagement of temporal attention in left spatial neglect

Previous literature showed how left spatial neglect arises from an asymmetrical distribution of spatial attention. However, it was also suggested that left spatial neglect might be partially caused or at least worsened by non-spatial attention disorders of the right-lateralized stimulus-driven attentional fronto-parietal network. Here, we psychophysically tested the efficiency of temporal attentional engagement of foveal perception through meta-contrast (Experiment 1) and "attentional" masking (Experiment 2) tasks in patients with right-hemisphere stroke with left neglect (N+), without left neglect (N-) and matched healthy controls (C). In both experiments, N+ patients showed higher thresholds, not only than Cs, but also than N- patients. Temporal engagement was clinically impaired in all N+ patients and highly correlated with their typical inability to direct spatial attention towards stimuli on the left side. Our findings suggest that a temporal impairment of attentional engagement is a relevant deficit of left spatial neglect.

Temporal and Spatial Information Elicit Different Power and Connectivity Profiles during Working Memory Maintenance

Working memory (WM) is the cognitive ability to store and manipulate information necessary for ongoing tasks. Although frontoparietal areas are involved in the retention of visually presented information, oscillatory neural activity differs for temporal and spatial WM processing. In this study, we corroborated previous findings describing the modulation of neural oscillations and expanded our investigation to the network organization underlying the cognitive processing of temporal and spatial information. We utilized MEG recordings during a Sternberg visual WM task. The spectral oscillatory activity in the maintenance phase revealed increased frontal theta (4-8 Hz) and parietal beta (13-30 Hz) in the temporal condition. Source level coherence analysis delineated the prominent role of parietal areas in all frequency bands during the maintenance of temporal information, whereas frontal and central areas showed major contributions in theta and beta ranges during the maintenance of spatial information. Our study revealed distinct spectral profiles of neural oscillations for separate cognitive subdomains of WM processing. The delineation of specific functional networks might have important implications for clinical applications, enabling the development of stimulation protocols targeting cognitive disabilities associated with WM impairments.

The domain-specificity of serial order working memory

Making a turn while driving is simple: turn on the indicator, check for cars, then turn. Two types of information are required to perform this sequence of events: information about the items (e.g., the correct indicator), and the serial order of those items (e.g., checking before turning rather than vice-versa). Previous research has found distinct working memory capacities (WMCs) for item and serial order information in both verbal and nonverbal domains. The current study investigates whether the serial order WMC is shared for sequences from different content domains. One hundred and fifty-three participants performed sequence matching tasks with verbal (letters and words) and nonverbal (locations and arrows) stimuli. The accuracy of detecting mismatched item-identity and serial order information in sequences was used to operationalize item and order WMC. Using structural equation modeling analyses, we directly compared models that included either domain-specific or domain-general serial order WMC latent variables, finding that models with domain-specific serial order WMC latent variables for verbal and nonverbal materials fit the data better than models with domain-general latent variables. The findings support the hypothesis that there are separate capacities for serial order working memory depending on the type of material being ordered.

A comparison of simultaneous and sequential visuo-spatial memory in children born very preterm

Research suggests that children born very preterm (≤32 weeks' gestation) are at greater risk of impairments in information processing (particularly when information is presented simultaneously rather than sequentially) and visuo-spatial short-term and working memory relative to children born at term. This study compared the performance of children born very preterm with their term-born peers to elucidate the nature of group differences in these areas. 113 children (65 very preterm; 48 term-born) aged 8-to-11 years completed four visuo-spatial recall tasks. Tasks varied by presentation type (simultaneous or sequential) and memory type (short-term or working memory). Both groups recalled more locations in simultaneous than sequential tasks, and in short-term than working memory tasks. In short-term memory tasks, children born at term recalled more locations than children born very preterm for the sequential task, but groups did not differ on the simultaneous task. The opposite pattern was observed in the working memory tasks, with no group differences on the sequential task, but better performance on the simultaneous task for children born at term. Our findings indicate that simultaneous processing may not be impaired in children born very preterm per se, with poorer performance observed only under high cognitive demand. This interaction suggests very preterm birth may affect the level of cognitive resources available during feature integration, the consequences of which become apparent when resources are already stretched. The impact of interactions with cognitive demand in this population should be an important consideration for educational support strategies, and for assessment in research and clinic.

From competition to cooperation: Visual neglect across the hemispheres

Visuospatial neglect is a frequent and disabling consequence of injuries to the right hemisphere. Patients with neglect show signs of impaired attention for left-sided events, which depends on dysfunction of fronto-parietal networks. After unilateral injury, such as stroke, these networks and their contralateral homologs can reorganize following multiple potential trajectories, which can be either adaptive or maladaptive. This article presents possible factors influencing the profile of evolution of neglect towards recovery or chronicity, and highlights potential mechanisms that may constrain these processes in time and space. The integrity of white matter pathways within and between the hemisphere appears to pose crucial connectivity constraints for compensatory brain plasticity from remote brain regions. Specifically, the availability of a sufficient degree of inter-hemispheric connectivity might be critical to shift the role of the undamaged left hemisphere in spatial neglect, from exerting maladaptive effects, to promoting compensatory activity.

Toward an integrative model accounting for typical and atypical development of visuospatial short-term memory

The origin of visuospatial short-term memory (STM) impairment is poorly investigated and is generally considered to be the result of a more global visuospatial deficit. However, previous studies suggest an important influence of two elements on performance in visuospatial STM tasks, the mode of presentation (i.e., simultaneous and sequential), and the visuospatial arrangement (structured vs. unstructured). With regards to a recent proposal, the aim of this study was to examine the development of the two modes of presentation and the visuospatial arrangement of visuospatial information in STM in a hundred typically developing participants aged from 4 years old to adults. Moreover, we also examined how the model explains the pattern of visuospatial STM deficit in two neurodevelopmental syndromes with different profiles in terms of STM abilities, namely Williams syndrome and Down syndrome. We found distinct performance for sequential and simultaneous presentation only from 11 years old with better performance in simultaneous than in sequential presentation mode and a sensitivity to visuospatial arrangement that increases with age. Both syndromes presented deficits at different levels, people with Williams syndrome for visuospatial arrangement and with Down syndrome for simultaneous visuospatial information in STM. The results demonstrate the importance to consider the influence of preexisting visuospatial knowledge on STM abilities. A two processing route model of STM is an interesting framework to interpret the different results.

Using working memory performance to predict mathematics performance 2 years on

A number of previous studies have used working memory components to predict mathematical performance in a variety of ways; however, there is no consideration of the contributions of the subcomponents of visuospatial working memory to this prediction. In this paper we conducted a 2-year follow-up to the data presented in Allen et al. (Q J Exp Psychol 73(2):239–248, 2020b) to ascertain how these subcomponents of visuospatial working memory related to later mathematical performance. 159 children (M age = 115.48 months) completed the maths test for this second wave of the study. Results show a shift from spatial–simultaneous influence to spatial–sequential influence, whilst verbal involvement remained relatively stable. Results are discussed in terms of their potential for education and future research.

The relationship between visuospatial neglect, spatial working memory and search behavior

Visuospatial neglect (VSN) is characterized by a lateralized attentional deficit in the visual domain. In addition, patients with VSN might have an impairment in the temporary storage of spatial information in working memory (spatial working memory; SWM) that, like VSN, could impair systematic searching behavior. Several studies have demonstrated either SWM impairments or impaired searching behavior in VSN patients. Here, we related SWM performance to search behavior in patients with and without VSN. We assessed SWM using a novel task in a group of 182 stroke patients (24 with VSN, 158 without) and 65 healthy controls. We related SWM performance to available stroke-related and cognitive data. Patients with VSN exhibited lower SWM performance than patients without VSN and healthy controls. Additional control analyses indicated that differences in SWM performance are specific to visuospatial processing, instead of e.g. verbal working memory or the general level of physical disability. Last, we related SWM performance to visual search performance on cancellation tasks, one where their cancellation markings remained visible and another one where their prior cancellations markings were invisible to the patient and therefore patients had to remember which targets they had canceled. SWM performance correlated with search organization. Together, these results from a large sample of stroke patients corroborate the findings of earlier studies, while excluding several alternative explanations: SWM impairment is a part of the neglect syndrome, and SWM impairments are related to search behavior.

Different patterns of confabulation in left visuo-spatial neglect

Confabulating patients produce statements and actions that are unintentionally incongruous to their history, background, present and future situation. Here we present the very unusual case of a patient with right hemisphere damage and signs of left visual neglect, who, when presented with visual stimuli, confabulated both for consciously undetected and for consciously detected left-sided details. Advanced anatomical investigation suggested a disconnection between the parietal and the temporal lobes in the right hemisphere. A disconnection between the ventral cortical visual stream and the dorsal fronto-parietal networks in the right hemisphere may contribute to confabulatory behaviour by restricting processing of left-sided stimuli to pre-conscious stages in the ventral visual stream.

The effect of visual arrangement on visuospatial short-term memory: Insights from children with 22q11.2 deletion syndrome

Recent models of visuospatial (VSSP) short-term memory postulate the existence of two dissociable mechanisms depending on whether VSSP information is presented simultaneously or sequentially. However, they do not specify to what extent VSSP short-term memory is under the influence of general VSSP processing. This issue was examined in people with 22q11.2 deletion syndrome, a genetic condition involving a VSSP deficit. The configuration of VSSP information was manipulated (structured vs. unstructured) to explore the impact of arrangement on VSSP short-term memory. Two presentation modes were used to see whether the VSSP arrangement has the same impact on simultaneous and sequential short-term memory. Compared to children matched on chronological age, children with 22q11.2 deletion syndrome showed impaired performance only for structured arrangement, regardless of the presentation mode, suggesting an influence of VSSP processing on VSSP short-term memory abilities. A revised cognitive architecture for a model of VSSP short-term memory is proposed.

Hemispatial neglect and serial order in verbal working memory

Working memory refers to our ability to actively maintain and process a limited amount of information during a brief period of time. Often, not only the information itself but also its serial order is crucial for good task performance. It was recently proposed that serial order is grounded in spatial cognition. Here, we compared performance of a group of right hemisphere-damaged patients with hemispatial neglect to healthy controls in verbal working memory tasks. Participants memorized sequences of consonants at span level and had to judge whether a target consonant belonged to the memorized sequence (item task) or whether a pair of consonants were presented in the same order as in the memorized sequence (order task). In line with this idea that serial order is grounded in spatial cognition, we found that neglect patients made significantly more errors in the order task than in the item task compared to healthy controls. Furthermore, this deficit seemed functionally related to neglect severity and was more frequently observed following right posterior brain damage. Interestingly, this specific impairment for serial order in verbal working memory was not lateralized. We advance the hypotheses of a potential contribution to the deficit of serial order in neglect patients of either or both (1) reduced spatial working memory capacity that enables to keep track of the spatial codes that provide memorized items with a positional context, (2) a spatial compression of these codes in the intact representational space.

Implicit learning: A way to improve visual search in spatial neglect?

Studies have shown that neglect patients are able to use stimulus regularities to orient faster toward the neglected side, without necessarily being aware of that information, or at the very least without being able to verbalize their knowledge. In order to better control for the involvement of explicit processes, the present study sought to test neglect patients' ability to detect more complex associations between stimuli using tasks similar to those used in implicit learning studies. Our results demonstrate that neglect patients had difficulties implicitly learning complex associations, contrary to what we found with controls. The possible influence of attentional and working memory impairments are discussed.