The Influence of Alertness on the Spatial Deployment of Visual Attention is Mediated by the Excitability of the Posterior Parietal Cortices

The Neurophysiological Features Associated with Unilateral Spatial Neglect Recovery: A Scoping Review

The purpose of this scoping review is to provide updated information on the neural basis and neurophysiological features associated with unilateral spatial neglect (USN) recovery. We applied the Preferred Reporting Systems for Systematic Reviews and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) framework and identified 16 relevant papers from the databases. Critical appraisal was performed by two independent reviewers using a standardized appraisal instrument developed by the PRISMA-ScR. We identified and categorized investigation methods for the neural basis and neurophysiological features of USN recovery after stroke using magnetic resonance imaging (MRI), functional MRI, and electroencephalography (EEG). This review found two brain-level mechanisms underlying USN recovery at the behavioral level. These include the absence of stroke-related damage to the right ventral attention network during the acute phase and compensatory recruitment of analogous areas of the undamaged opposite hemisphere and prefrontal cortex during visual search tasks in the subacute or later phases. However, the relationship between the neural and neurophysiological findings and improvements in USN-related activities of daily living remains unknown. This review adds to the growing body of evidence regarding the neural mechanisms underlying USN recovery.

Spatial asymmetries ("pseudoneglect") in free visual exploration-modulation of age and relationship to line bisection

When humans visually explore an image, they typically tend to start exploring its left side. This phenomenon, so-called pseudoneglect, is well known, but its time-course has only sparsely been studied. Furthermore, it is unclear whether age influences pseudoneglect, and the relationship between visuo-spatial attentional asymmetries in a free visual exploration task and a classical line bisection task has not been established. To address these questions, 60 healthy participants, aged between 22 and 86, were assessed by means of a free visual exploration task with a series of naturalistic, colour photographs of everyday scenes, while their gaze was recorded by means of a contact-free eye-tracking system. Furthermore, a classical line bisection task was administered, and information concerning handedness and subjective alertness during the experiment was obtained. The results revealed a time-sensitive window during visual exploration, between 260 and 960 ms, in which age was a significant predictor of the leftward bias in gaze position, i.e., of pseudoneglect. Moreover, pseudoneglect as assessed by the line bisection task correlated with the average gaze position throughout a time-window of 300–1490 ms during the visual exploration task. These results suggest that age influences visual exploration and pseudoneglect in a time-sensitive fashion, and that the degree of pseudoneglect in the line bisection task correlates with the average gaze position during visual exploration in a time-sensitive manner.

Trial-by-trial co-variation of pre-stimulus EEG alpha power and visuospatial bias reflects a mixture of stochastic and deterministic effects

Human perception of perithreshold stimuli critically depends on oscillatory EEG activity prior to stimulus onset. However, it remains unclear exactly which aspects of perception are shaped by this pre‐stimulus activity and what role stochastic (trial‐by‐trial) variability plays in driving these relationships. We employed a novel jackknife approach to link single‐trial variability in oscillatory activity to psychometric measures from a task that requires judgement of the relative length of two line segments (the landmark task). The results provide evidence that pre‐stimulus alpha fluctuations influence perceptual bias. Importantly, a mediation analysis showed that this relationship is partially driven by long‐term (deterministic) alpha changes over time, highlighting the need to account for sources of trial‐by‐trial variability when interpreting EEG predictors of perception. These results provide fundamental insight into the nature of the effects of ongoing oscillatory activity on perception. The jackknife approach we implemented may serve to identify and investigate neural signatures of perceptual relevance in more detail.