Beyond Time and Space:The Effect of a Lateralized Sustained Attention Task and Brain Stimulation on Spatial and Selective Attention

The Theory of Visual Attention (TVA) provides a mathematical formalisation of the “biased competition” account of visual attention. Applying this model to individual performance in a free recall task allows the estimation of 5 independent attentional parameters: visual short-term memory (VSTM) capacity, speed of information processing, perceptual threshold of visual detection; attentional weights representing spatial distribution of attention (spatial bias), and the top-down selectivity index. While the TVA focuses on selection in space, complementary accounts of attention describe how attention is maintained over time, and how temporal processes interact with selection. A growing body of evidence indicates that different facets of attention interact and share common neural substrates. The aim of the current study was to modulate a spatial attentional bias via transfer effects, based on a mechanistic understanding of the interplay between spatial, selective and temporal aspects of attention. Specifically, we examined here: (i) whether a single administration of a lateralized sustained attention task could prime spatial orienting and lead to transferable changes in attentional weights (assigned to the left vs right hemi-field) and/or other attentional parameters assessed within the framework of TVA (Experiment 1); (ii) whether the effects of such spatial-priming on TVA parameters could be further enhanced by bi-parietal high frequency transcranial random noise stimulation (tRNS) (Experiment 2). Our results demonstrate that spatial attentional bias, as assessed within the TVA framework, was primed by sustaining attention towards the right hemi-field, but this spatial-priming effect did not occur when sustaining attention towards the left. Furthermore, we show that bi-parietal high-frequency tRNS combined with the rightward spatial-priming resulted in an increased attentional selectivity. To conclude, we present a novel, theory-driven method for attentional modulation providing important insights into how the spatial and temporal processes in attention interact with attentional selection

Right fronto-parietal networks mediate the neurocognitive benefits of enriched environments

Exposure to enriched environments throughout a lifetime, providing so called reserve, protects against cognitive decline in later years. It has been hypothesised that high levels of alertness necessitated by enriched environments might strengthen the right fronto-parietal networks to facilitate this neurocognitive resilience. We have previously shown that enriched environments offset age-related deficits in selective attention by preserving grey matter within right fronto-parietal regions. Here, using neurite orientation dispersion and density imaging, we examined the relationship between enriched environments, microstructural properties of fronto-parietal white matter association pathways (three branches of the superior longitudinal fasciculus), structural brain health (atrophy), and attention (alertness, orienting and executive control) in a group of older adults. We show that exposure to enriched environments is associated with a lower orientation dispersion index within the right superior longitudinal fasciculus 1 which in turn mediates the relationship between enriched environments and alertness, as well as grey- and white-matter atrophy. This suggests that enriched environments may induce white matter plasticity (and prevent age-related dispersion of axons) within the right fronto-parietal networks to facilitate the preservation of neurocognitive health in later years

Large expert-curated database for benchmarking document similarity detection in biomedical literature search

Document recommendation systems for locating relevant literature have mostly relied on methods developed a decade ago. This is largely due to the lack of a large offline gold-standard benchmark of relevant documents that cover a variety of research fields such that newly developed literature search techniques can be compared, improved and translated into practice. To overcome this bottleneck, we have established the RElevant LIterature SearcH consortium consisting of more than 1500 scientists from 84 countries, who have collectively annotated the relevance of over 180 000 PubMed-listed articles with regard to their respective seed (input) article/s. The majority of annotations were contributed by highly experienced, original authors of the seed articles. The collected data cover 76% of all unique PubMed Medical Subject Headings descriptors. No systematic biases were observed across different experience levels, research fields or time spent on annotations. More importantly, annotations of the same document pairs contributed by different scientists were highly concordant. We further show that the three representative baseline methods used to generate recommended articles for evaluation (Okapi Best Matching 25, Term Frequency-Inverse Document Frequency and PubMed Related Articles) had similar overall performances. Additionally, we found that these methods each tend to produce distinct collections of recommended articles, suggesting that a hybrid method may be required to completely capture all relevant articles. The established database server located at https://relishdb.ict.griffith.edu.au is freely available for the downloading of annotation data and the blind testing of new methods. We expect that this benchmark will be useful for stimulating the development of new powerful techniques for title and title/abstract-based search engines for relevant articles in biomedical research.Peer reviewe

Methodological considerations and cognitive factors underlying sustained attention

The active, ongoing maintenance of an adequate level of performance over time on task is an essential cognitive faculty, and has been described in multiple frameworks since the earliest days of cognitive research. Theoretical accounts of performance maintenance focused on the timely fluctuations of attention components, using the partially overlapping constructs of sustained attention, arousal, vigilance and alertness. In this thesis, particular attention is given to sustained attention, arguably the most useful and frequently used construct in a clinical context. Chapter 1 provides an introductory overview of the literature, focusing on the theories and paradigms available to assess sustained attention and other closely related constructs. Chapter 2 introduces a new task for assessing sustained attention, based on a variation of the Continuous Performance Task (CPT), and discusses the contribution of various task factors to performance patterns. In Chapter 3, the newly established paradigm is used to assess sustained attention among stroke survivors and the healthy ageing, and relate task-performance to subjective reports of daily lapses in attention. A detailed discussion is devoted to identifying the task indices that best represent sustained attention capacity, favouring measures incorporating the notion of change in performance over time. Chapter 4 applies the same approach of estimating change in performance over time to studying sustained attention among children with genetic developmental disorders. Chapters 5 and 6 show how performance in a CPT is influenced by the pace at which stimuli are presented in the task. It is argued that individuals are sensitive to varying levels of temporal regularities; consequently, when measuring sustained attention, researchers must account for the rhythmic pattern that the CPT may introduce. Chapter 7 will present an intervention study combining brain stimulation and a spatially-lateralised CPT paradigm, demonstrating changes in components of Selective Attention as defined by a computational model. The thesis is concluded in Chapter 8, which discusses the contributions of the experimental findings to the understanding of sustained attention and associated experimental methods. The thesis proposes a clear mapping of sustained attention with relation to other closely related constructs, and attempts to provide useful tools for improving clinical assessment

Mackworth’s clock is still ticking

Even the easiest task can become difficult if repeated over extended time: spotting a spelling mistake in a single sentence is straightforward, but reviewing a long text is more challenging

Transient Blocking Synchronization

We introduce Transient Blocking Synchronization (TBS), a new approach to hardware synchronization for mega-scale distributed-memory multiprocessor machines. Such machines, with thousands of processors and controller based memory modules, are essentially distributed networks, and one must search for new paradigms that provide hardware synchronization support with high levels of robustness and minimal protocol and communication overhead. It is our claim that the semantics of non-blocking synchronization primitives such as Compare&Swap and LoadLinked/StoreConditional on the one hand, and blocking ones such as Full/Empty-bits on the other, will introduce high communication and space costs when implemented on large scale machines. TBS is a novel hardware synchronization paradigm resting between the classic blocking and non-blocking approaches to synchronization. It is an example of how, based on very weak ‘‘transient’ ’ hardware blocking, that is, blocking that may be revoked at any time, one can provide non-blocking universal synchronization with low communication and space complexity. This paper presents a set of simple TBS single-location synchronization operations and shows that they provide low cost non-blocking emulations of all known read-modify-write operations. Moreover, it shows that the combination of TBS with hardware supported transactional bits, a variation on traditional hardware full/empty bits, can provide low message cost implementations of multi-word transactional operations