Duncan E. Astle

Orienting attention to locations in mental representations

Many cognitive processes depend on our ability to hold information in mind, often well beyond the offset of the original sensory input. The capacity of this visual short-term memory (VSTM) is limited to around three to four items. Recent research has demonstrated that the content of VSTM can be modulated by top-down attentional biases. This has been demonstrated using retrodictive spatial cues, termed “retro-cues,” which orient subjects’ attention to spatial locations within VSTM. In the present article, we tested whether the use of these cues is modulated by memory load and cue delay. There are a number of important conclusions: (1) Top-down biases can operate on very brief iconic traces as well as on older VSTM representations (Exp. 1). (2) When operating within capacity, subjects use the cue to prioritise where they initiate their memory search, rather than to discard uncued items (Exps. 2 and 3). (3) When capacity is exceeded, there is little benefit to top-down biasing relative to a neutral condition; however, unattended items are lost, with there being a substantial cost of invalid spatial cueing (Exp. 3). (4) These costs and benefits of orienting spatial attention differ across iconic memory and VSTM representations when VSTM capacity is exceeded (Exp. 4).

Cognitive Training Enhances Intrinsic Brain Connectivity in Childhood

In human participants, the intensive practice of particular cognitive activities can induce sustained improvements in cognitive performance, which in some cases transfer to benefits on untrained activities. Despite the growing body of research examining the behavioral effects of cognitive training in children, no studies have explored directly the neural basis of these training effects in a systematic, controlled fashion. Therefore, the impact of training on brain neurophysiology in childhood, and the mechanisms by which benefits may be achieved, are unknown. Here, we apply new methods to examine dynamic neurophysiological connectivity in the context of a randomized trial of adaptive working memory training undertaken in children. After training, connectivity between frontoparietal networks and both lateral occipital complex and inferior temporal cortex was altered. Furthermore, improvements in working memory after training were associated with increased strength of neural connectivity at rest, with the magnitude of these specific neurophysiological changes being mirrored by individual gains in untrained working memory performance.

Attentional control constrains visual short-term memory: insights from developmental and individual differences.

The mechanisms by which attentional control biases mnemonic representations have attracted much interest but remain poorly understood. As attention and memory develop gradually over childhood and variably across individuals, assessing how participants of different ages and ability attend to mnemonic contents can elucidate their interplay. In Experiment 1, 7-year-olds, 10-year-olds, and adults were asked to report whether a probe item had been part of a previously presented four-item array. The initial array could either be uncued, be preceded (“precued”), or followed (“retrocued”) by a spatial cue orienting attention to one of the potential item locations. Performance across groups was significantly improved by both cue types, and individual differences in childrens retrospective attentional control predicted their visual short-term and working memory span, whereas their basic ability to remember in the absence of cues did not. Experiment 2 imposed a variable delay between the array and the subsequent orienting cue. Cueing benefits were greater in adults than in 10-year-olds, but they persisted even when cues followed the array by nearly 3 seconds, suggesting that orienting operated on durable short-term representations for both age groups. The findings indicate that there are substantial developmental and individual differences in the ability to control attention to memory and that in turn these differences constrain visual short-term memory capacity.

Spatial selection of features within perceived and remembered objects.

Our representation of the visual world can be modulated by spatially specific attentional biases that depend flexibly on task goals. We compared searching for task-relevant features in perceived versus remembered objects. When searching perceptual input, selected task-relevant and suppressed task-irrelevant features elicited contrasting spatiotopic ERP effects, despite them being perceptually identical. This was also true when participants searched a memory array, suggesting that memory had retained the spatial organization of the original perceptual input and that this representation could be modulated in a spatially specific fashion. However, task-relevant selection and task-irrelevant suppression effects were of the opposite polarity when searching remembered compared to perceived objects. We suggest that this surprising result stems from the nature of feature- and object-based representations when stored in visual short-term memory. When stored, features are integrated into objects, meaning that the spatially specific selection mechanisms must operate upon objects rather than specific feature-level representations.

Using developmental cognitive neuroscience to study behavioral and attentional control.

Adult cognitive neuroscience employs a wide variety of techniques to investigate a broad range of behavioral and cognitive functions. One prominent area of study is that of executive control, complemented by a smaller but growing literature exploring the developmental cognitive neuroscience of executive control. To date this approach has often compared children with specific developmental disorders, such as ADHD and ASD, with typically developing controls. Whilst these comparisons have done much to advance our understanding of the neural markers that underpin behavioral difficulties at specific time-points in development, we contend that they should leave developmental cognitive neuroscientists wanting. Studying the neural correlates of typical changes in executive control in their own right can reveal how different neural mechanisms characteristic of the adult end-state emerge, and it can therefore inform the adult cognitive neuroscience of executive control itself. The current review addresses the extent to which developmentalists and adult cognitive neuroscientists have tapped this common ground. Some very elegant investigations illustrate how seemingly common processes in adulthood present as separable in childhood, on the basis of their distinctive developmental trajectories. These demonstrations have implications not only for an understanding of changing behavior from infancy through childhood and adolescence into adulthood, but, moreover, for our grasp of the adult end-state per se. We contend that, if used appropriately, developmental cognitive neuroscience could enable us to construct a more mechanistic account of executive control.

Orienting Attention Within Visual Short-Term Memory: Development and Mechanisms

How does developing attentional control operate within visual short-term memory (VSTM)? Seven-year-olds, 11-year-olds, and adults (total n = 205) were asked to report whether probe items were part of preceding visual arrays. In Experiment 1, central or peripheral cues oriented attention to the location of to-be-probed items either prior to encoding or during maintenance. Cues improved memory regardless of their position, but younger children benefited less from cues presented during maintenance, and these benefits related to VSTM span over and above basic memory in uncued trials. In Experiment 2, cues of low validity eliminated benefits, suggesting that even the youngest children use cues voluntarily, rather than automatically. These findings elucidate the close coupling between developing visuospatial attentional control and VSTM.

Subliminally Presented and Stored Objects Capture Spatial Attention

When objects disappear from view, we can still bring them to mind, at least for brief periods of time, because we can represent those objects in visual short-term memory (VSTM) (Sperling, 1960; Cowan, 2001). A defining characteristic of this representation is that it is topographic, that is, it preserves a spatial organization based on the original visual percept (Vogel and Machizawa, 2004; Astle et al., 2009; Kuo et al., 2009). Recent research has also shown that features or locations of visual items that match those being maintained in conscious VSTM automatically capture our attention (Awh and Jonides, 2001; Olivers et al., 2006; Soto et al., 2008). But do objects leave some trace that can guide spatial attention, even without participants intentionally remembering them? Furthermore, could subliminally presented objects leave a topographically arranged representation that can capture attention? We presented objects either supraliminally or subliminally and then 1 s later re-presented one of those objects in a new location, as a “probe” shape. As participants made an arbitrary perceptual judgment on the probe shape, their covert spatial attention was drawn to the original location of that shape, regardless of whether its initial presentation had been supraliminal or subliminal. We demonstrate this with neural and behavioral measures of memory-driven attentional capture. These findings reveal the existence of a topographically arranged store of “visual” objects, the content of which is beyond our explicit awareness but which nonetheless guides spatial attention.

The role of spatial information in advance task-set control: an event-related potential study

Task‐switching has proved to be a fruitful paradigm for studying cognitive control mechanisms. Interestingly, this avenue of study has revealed that subjects are, to some degree, able to bring about a change in task‐set prior to the performance of that task (provided that they are given advance warning of the upcoming task, for instance in the form of a cue). Event‐related potentials (ERPs) have proved to be a good way of measuring these rapid anticipatory control processes. To explore these processes further, the current study examined the relationship between the availability of spatial information and cue‐locked task‐switching ERP effects. Two groups of subjects were compared: one group could separate the task‐sets on the basis of the targets’ colour (the ‘colour’ group), the second on the basis of the targets’ location (the ‘spatial’ group). The performance of both groups benefited to the same extent from advance cueing of task‐transitions (switches or repeats), yet the ERP data revealed cue‐locked (but not target‐locked) differences between the two groups. The most striking of these differences was the absence of both a late positivity over posterior scalp and a late negativity over frontal scalp when the spatial group switched between tasks. Thus, it seems unlikely that these effects index stimulus‐response ‘reconfiguration’per se– as the mappings were identical for both groups of subjects – but rather that these task‐switching processes are sensitive to how the mappings are represented.

Age group and individual differences in attentional orienting dissociate neural mechanisms of encoding and maintenance in visual stm

Selective attention biases the encoding and maintenance of representations in visual STM (VSTM). However, precise attentional mechanisms gating encoding and maintenance in VSTM and across development remain less well understood. We recorded EEG while adults and 10-year-olds used cues to guide attention before encoding or while maintaining items in VSTM. Known neural markers of spatial orienting to incoming percepts, that is, Early Directing Attention Negativity, Anterior Directing Attention Negativity, and Late Directing Attention Positivity, were examined in the context of orienting within VSTM. Adults elicited a set of neural markers that were broadly similar in preparation for encoding and during maintenance. In contrast, in children these processes dissociated. Furthermore, in children, individual differences in the amplitude of neural markers of prospective orienting related to individual differences in VSTM capacity, suggesting that children with high capacity are more efficient at selecting information for encoding into VSTM. Finally, retrospective, but not prospective, orienting in both age groups elicited the well-known marker of visual search (N2pc), indicating the recruitment of additional neural circuits when orienting during maintenance. Developmental and individual differences differentiate seemingly similar processes of orienting to perceptually available representations and to representations held in VSTM.

Electrophysiological Measures of Resting State Functional Connectivity and Their Relationship with Working Memory Capacity in Childhood.

Abstract Functional connectivity is the statistical association of neuronal activity time courses across distinct brain regions, supporting specific cognitive processes. This coordination of activity is likely to be highly important for complex aspects of cognition, such as the communication of fluctuating task goals from higher‐order control regions to lower‐order, functionally specific regions. Some of these functional connections are identifiable even when relevant cognitive tasks are not being performed (i.e. at rest). We used magnetoencephalographic recordings projected into source space to demonstrate that resting state networks in childhood have electrophysiological underpinnings that are evident in the spontaneous fluctuations of oscillatory brain activity. Using the temporal structure of these oscillatory patterns we were able to identify a number of functional resting state networks analogous to those reported in the adult literature. In a second analysis we fused this dynamic temporal information with the spatial information from a functional magnetic resonance imaging analysis of functional connectivity, to demonstrate that inter‐subject variability in these electrophysiological measures of functional connectivity is correlated with individual differences in cognitive ability: the strength of connectivity between a fronto‐parietal network and lower‐level processing areas in inferior temporal cortex was associated with spatial working memory capacity, as measured outside the scanner with educationally relevant standardized assessments. This study represents the first exploration of the electrophysiological mechanisms underpinning resting state functional connectivity in source space in childhood, and the extent to which the strength of particular connections is associated with cognitive ability.