Behavioural evidence for separating components within visuo-spatial working memory

Several different sources of evidence support the idea that visuo-spatial working memory can be segregated into separate cognitive subsystems. However, the nature of these systems remains unclear. Recently we reported data from neurological patients suggesting that information about visual appearance is retained in a different subsystem from information about spatial location. In this paper we report latency data from neurologically intact participants showing an experimental double dissociation between memory for appearance and memory for location. This was achieved by use of a selective dual task interference technique. This pattern provides evidence supporting the segregation of visuo-spatial memory between two systems, one of which supports memory for stimulus appearance and the other which supports memory for spatial location.     

Dissociation between appearance and location within visuo-spatial working memory

Previous research has demonstrated separation between systems supporting memory for appearance and memory for location. However, the interpretation of these results is complicated by a confound occurring because of the simultaneous presentation of objects in multiple-item arrays when assessing memory for appearance and the sequential presentation of items when assessing memory for location. This paper reports an experiment in which sequential or simultaneous modes of presentation were factorially manipulated with memory for visual appearance or memory for location. Spatial interference (tapping) or visual interference (dynamic visual noise) were presented during retention. Appearance versus location interacted with the type of interference task, but mode of presentation did not. These results are consistent with the view that different subsystems within visuo-spatial working memory support memory for appearance and memory for location.     

Movement and visual coding: the structure of visuo-spatial working memory

The influential model of verbal working memory (WM) introduced by Baddeley and Hitch (Recent advances in learning and motivation. Academic, New York, 1974) comprised three interacting component parts; an executive controller and two subservient systems. The two subservient systems, one underpinning verbal processing and the other underpinning visual processing are themselves subdivided. In the verbal system, a passive phonological store is maintained by an active phonological loop, which is able to rehearse the material in the passive store. The visual working memory system has traditionally been thought of as having a similar architecture with a passive visual store being maintained by an active store, which codes in terms of movement over space. The paper discusses the evidence for this relationship in visuo-spatial WM and concludes that the architecture does not fit well with the experimental literature. A direction for future research is suggested.     

Oculomotor involvement in spatial working memory is task-specific

Many everyday tasks, such as remembering where you parked, require the capacity to store and manipulate information about the visual and spatial properties of the world. The ability to represent, remember, and manipulate spatial information is known as visuospatial working memory (VSWM). Despite substantial interest in VSWM the mechanisms responsible for this ability remain debated. One influential idea is that VSWM depends on activity in the eye-movement (oculomotor) system. However, this has proved difficult to test because experimental paradigms that disrupt oculomotor control also interfere with other cognitive systems, such as spatial attention. Here, we present data from a novel paradigm that selectively disrupts activation in the oculomotor system. We show that the inability to make eye-movements is associated with impaired performance on the Corsi Blocks task, but not on Arrow Span, Visual Patterns, Size Estimation or Digit Span tasks. It is argued that the oculomotor system is required to encode and maintain spatial locations indicted by a change in physical salience, but not non-salient spatial locations indicated by the meaning of a symbolic cue. This suggestion offers a way to reconcile the currently conflicting evidence regarding the role of the oculomotor system in spatial working memory.     

Reconsidering the two-second decay hypothesis in verbal working memory

A common belief in the study of short-term memory is that the verbal trace decays around two seconds after it is encoded. This belief is typically assumed to follow from the finding that in immediate serial recall, the time required to rapidly articulate a span-length list is around two seconds. Empirically, this belief is in opposition to a broad set of findings across a number of domains that establish mean decay times to be longer than two seconds. Theoretically, the available computational and mathematical models of immediate serial recall do not address this issue directly, because they typically rely on other mechanisms in addition to decay to account for forgetting. As such, they may show that decay times can be longer than two seconds, but they fail to show that they cannot be as short as two seconds. We address the issue directly and set a lower bound on mean trace decay times, even under the limiting assumption that all forgetting is due to trace decay. We do this by presenting a simple item-based model of trace decay that allows us to estimate values of mean trace duration. For a set of words whose span-length lists can be rapidly articulated in about two seconds, the model offers a conservative estimate for their mean decay times of around four seconds. Both the experimental and theoretical evidence show that items in verbal working memory decay considerably slower than the two-second decay hypothesis claims.     

A cognitive approach to dogmatism: An investigation into the relationship of verbal working memory and dogmatism

This study investigated the relationship of working memory to open and closed belief systems. Two hundred college students completed a working memory span test to measure verbal working memory, and Rokeach’s Dogmatism Scale (1956). Regression analysis was undertaken to determine the contribution of verbal working memory to dogmatism. A negative correlation was found between dogmatism scores and working memory scores (p = .002) confirming the hypothesis that those participants who display a larger working memory capacity would show lower levels of dogmatic beliefs than participants displaying a smaller working memory capacity. Error analysis was employed to determine the significance of inhibition processes; indicating that capacity limits in verbal working memory, and not processing deficits, were primarily responsible for poor working memory scores. Dogmatism was not found to be related to gender, age, ethnicity, religious affiliation, academic major, or level of education.     

Brain activation and deactivation during location and color working memory tasks in 11-13-year-old children

Using functional magnetic resonance imaging (fMRI) and n-back tasks we investigated whether, in 11-13-year-old children, spatial (location) and nonspatial (color) information is differentially processed during visual attention (0-back) and working memory (WM) (2-back) tasks and whether such cognitive task performance, compared to a resting state, results in regional deactivation. The location 0-back task, compared to the color 0-back task, activated segregated areas in the frontal, parietal and occipital cortices whereas no differentially activated voxels were obtained when location and color 2-back tasks were directly contrasted. Several midline cortical areas were less active during 0- and 2-back task performance than resting state. The task-induced deactivation increased with task difficulty as demonstrated by larger deactivation during 2-back than 0-back tasks. The results suggest that, in 11-13-year-old children, the visual attentional network is differently recruited by spatial and nonspatial information processing, but the functional organization of cortical activation in WM in this age group is not based on the type of information processed. Furthermore, 11-13-year-old children exhibited a similar pattern of cortical deactivation that has been reported in adults during cognitive task performance compared to a resting state.     

Developmental changes in infants’ visual short-term memory for location

To examine the development of visual short-term memory (VSTM) for location, we presented 6- to 12-month-old infants (N = 199) with two side-by-side stimulus streams. In each stream, arrays of colored circles continually appeared, disappeared, and reappeared. In the changing stream, the location of one or more items changed in each cycle; in the non-changing streams the locations did not change. Eight- and 12.5-month-old infants showed evidence of memory for multiple locations, whereas 6.5-month-old infants showed evidence of memory only for a single location, and only when that location was easily identified by salient landmarks. In the absence of such landmarks, 6.5-month-old infants showed evidence of memory for the overall configuration or shape. This developmental trajectory for spatial VSTM is similar to that previously observed for color VSTM. These results additionally show that infants’ ability to detect changes in location is dependent on their developing sensitivity to spatial reference frames.     

Storage and processing in visuo-spatial working memory

Visuo-spatial working memory has been used to account for performance in a wide range of visuo-spatial tasks, including perceptuo-motor tracking and immediate recall of visually presented patterns. However a developing body of evidence points to a fractionation of the concept into visuo-spatial processing that calls on general purpose executive resources, and a visual 'cache' memory for temporary storage in on-line cognition. Two related experiments are described which address whether processing and temporary memory draw on overlapping or on distinct resources in working memory. Experiment 1 demonstrates that participants can accurately respond to a series of targets appearing in random locations whether or not they have the additional load of retaining and subsequently recalling the appearance of each target. Memory for target appearance likewise is largely unaffected by the additional load of requiring a response to each target. Experiment 2 demonstrates similar findings when verbal labeling of the patterns is inhibited through the use of articulatory suppression. Results are interpreted as consistent with a multiple component working memory system.     

The structure of working memory and how it relates to intelligence in children

This study explored the structure of working memory, and its relationship with intelligence in 176 typically-developing children in the 4th and 5th grades at school. Different measures of working memory (WM), and intelligence (g) were administered. Confirmatory factor analyses showed that WM involves an attentional control system and storage aspects that rely on domain-specific verbal (STM-V) and visuospatial (STM-VS) resources. The structural equation models showed that WM predicts a large portion (66%) of the variance in g, confirming that the two constructs are separable but closely related in young children. Findings also showed that only WM and STM-VS are significantly related to g, while the contribution of STM-V is moderate. Theoretical implications for the relationship between WM and g are discussed.     

Positive affect improves working memory: Implications for controlled cognitive processing

This study examined the effects of positive affect on working memory (WM) and short-term memory (STM). Given that WM involves both storage and controlled processing and that STM primarily involves storage processing, we hypothesised that if positive affect facilitates controlled processing, it should improve WM more than STM. The results demonstrated that positive affect, compared with neutral affect, significantly enhanced WM, as measured by the operation span task. The influence of positive affect on STM, however, was weaker. These results suggest that positive affect enhances WM, a task that involves controlled processing, not just storage processing. Additional analyses of recall and processing times and accuracy further suggest that improved WM under positive affect is not attributable to motivational differences, but results instead from improved controlled cognitive processing.     

Consciousness and working memory: Current trends and research perspectives

Working memory has long been thought to be closely related to consciousness. However, recent empirical studies show that unconscious content may be maintained within working memory and that complex cognitive computations may be performed on-line. This promotes research on the exact relationships between consciousness and working memory. Current evidence for working memory being a conscious as well as an unconscious process is reviewed. Consciousness is shown to be considered a subset of working memory by major current theories of working memory. Evidence for unconscious elements in working memory is shown to come from visual masking and attentional blink paradigms, and from the studies of implicit working memory. It is concluded that more research is needed to explicate the relationship between consciousness and working memory. Future research directions regarding the relationship between consciousness and working memory are discussed.     

The role of working memory components and visuospatial abilities in route learning within a virtual environment

An experiment was run to complete our understanding of the involvement of working memory (WM) components in the construction of a spatial model from visual input, considering some of the visuospatial abilities known to modulate performance. In addition, to allow for consideration of the flexibility of the spatial representation, routes in a virtual environment were presented with a route perspective, and tests were presented with route and survey perspectives. The results indicate that the verbal and spatial WM are only involved in the memorisation of certain types of information, and that their involvement depends on the change of perspective necessitated by the task. Thus, even when the learning material and the tests used to assess performance are only visual, a verbal recoding of some information is necessary. Moreover, individual differences modulate the involvement of WM; an individual with higher visuospatial capacities uses more spatial WM than an individual with lower spatial capacities.     

Children's working memory: Its structure and relationship to fluid intelligence

Working memory (WM) has been predominantly studied in adults. The insights provided by these studies have led to the development of competing theories on the structure of WM and conflicting conclusions on how strongly WM components are related to higher order thinking skills such as fluid intelligence. However, it remains unclear whether and to what extent the theories and findings derived from adult data generalize to children. The purpose of the present study is therefore to investigate children's WM (N = 161), who attended classes at the end of kindergarten in Luxembourg. Specifically, we examine different structural models of WM and how its components, as defined in these models, are related to fluid intelligence. Our results indicate that short-term storage capacity primarily explains the relationship between WM and fluid intelligence. Based on these observations we discuss the theoretical and methodological issues that arise when children's WM is investigated.     

The long-term effects of mild head injury on short-term memory for visual form, spatial location, and their conjunction in well-functioning university students

Research has suggested the presence of subtle long-term cognitive changes in otherwise well-functioning individuals who have previously sustained a mild head injury (MHI). This paper investigated the long-term effects of MHI on visual, spatial, and visual-spatial short-term memory in well-functioning university students. Sixteen students who reported having sustained a MHI were compared to 16 controls on tests of short-term memory (STM) for abstract polygons in haphazardly arranged locations. The three tests differed only in the requirements for recall (shapes for the visual task, locations for the spatial task, and the shapes in their respective locations for the visual-spatial task). MHI participants were selectively impaired on spatial memory, suggesting that tasks of spatial STM may be more sensitive, compared to tasks of visual STM, to the subtle long-term cognitive changes that may be present after a MHI.     

Visual working memory for dynamic objects: Impaired binding between object feature and location

In daily life, people frequently need to observe dynamic objects and temporarily maintain their representations in visual working memory (VWM). The present study explored the mechanism underlying the binding between perceptual features and locations of dynamic objects in VWM. In three experiments, we measured and compared the memory performance for feature-location binding of multiple dynamic and static objects. The results showed that the feature-location binding was impaired for the dynamic objects compared with the static objects. The impairment persisted when the global spatial configuration of the objects remained intact during the motion, as well as when the binding task was relatively easy, such as binding between single-feature objects and coarse locations. The results indicate that object features and locations are not maintained in VWM as well-integrated object files; rather, the formation of feature-location binding may require additional processes, which are disrupted by the constant change of locations in dynamic circumstances. We propose a consolidation process as possible underlying mechanism, and discuss factors that may influence the strength of feature-location binding in dynamic circumstances.     

Happiness increases verbal and spatial working memory capacity where sadness does not: Emotion,working memory and executive control

The effects of emotion on working memory and executive control are often studied in isolation. Positive mood enhances verbal and impairs spatial working memory, whereas negative mood enhances spatial and impairs verbal working memory. Moreover, positive mood enhances executive control, whereas negative mood has little influence. We examined how emotion influences verbal and spatial working memory capacity, which requires executive control to coordinate between holding information in working memory and completing a secondary task. We predicted that positive mood would improve both verbal and spatial working memory capacity because of its influence on executive control. Positive, negative and neutral moods were induced followed by completing a verbal (Experiment 1) or spatial (Experiment 2) working memory operation span task to assess working memory capacity. Positive mood enhanced working memory capacity irrespective of the working memory domain, whereas negative mood had no influence on performance. Thus, positive mood was more successful holding information in working memory while processing task-irrelevant information, suggesting that the influence mood has on executive control supersedes the independent effects mood has on domain-specific working memory.     

Children's use of semantic organizational strategies is mediated by working memory capacity

In adults, the ability to apply semantic grouping strategies has been found to depend on working memory. To investigate this relation in children, two sort-recall tasks (one without and one with a grouping instruction) were administered to 6–12-year-olds. The role of working memory was examined by means of mediation analyses and by assessing whether children who successfully used the semantic grouping strategy had higher working memory capacity than did children who did not show such strategy use. Only children aged 8–12 were able to successfully use semantic grouping strategies (and 8–9-year-olds only after instruction), while strategy use was absent in 6–7-year-olds. Both types of analysis involving working memory suggested that, also in children, working memory (and not short-term memory) mediates the development of successful use of the semantic grouping strategy during both encoding and retrieval.     

Release of inattentional blindness by high working memory load: elucidating the relationship between working memory and selective attention

An unexpected stimulus often remains unnoticed if attention is focused elsewhere. This inattentional blindness has been shown to be increased under conditions of high memory load. Here we show that increasing working memory load can also have the opposite effect of reducing inattentional blindness (i.e., improving stimulus detection) if stimulus detection is competing for attention with a concurrent visual task. Participants were required to judge which of two lines was the longer while holding in working memory either one digit (low load) or six digits (high load). An unexpected visual stimulus was presented once alongside the line judgment task. Detection of the unexpected stimulus was significantly improved under conditions of higher working memory load. This improvement in performance prompts the striking conclusion that an effect of cognitive load is to increase attentional spread, thereby enhancing our ability to detect perceptual stimuli to which we would normally be inattentionally blind under less taxing cognitive conditions. We discuss the implications of these findings for our understanding of the relationship between working memory and selective attention.     

Visual working memory retains movement information within an allocentric reference frame

What frame of reference do we use to remember observed movements? One possibility is that visual working memory (VWM) retains movement information using a retinotopic frame of reference: A coordinate system with respect to the retina that retains view-dependent information. Alternatively, VWM might retain movement information using an allocentric frame of reference: A coordinate system with respect to the scene that retains view-invariant information. To address this question, I examined whether VWM retains view-dependent or view-invariant movement information. Results show that (1) observers have considerable difficulty remembering from which viewpoints they observed movements after a few seconds' delay, and (2) the same number of movements can be retained in VWM whether the movements are encoded and tested from the same viewpoint or from different viewpoints. Thus, movement representations contain little to no view-dependent information, which suggests that VWM uses an allocentric reference frame to retain movement information.