Spatial attention: differential shifts in pseudoneglect direction with time-on-task and initial bias support the idea of observer subtypes

<p>Asymmetry in human spatial attention has long been documented. In the general population the majority of individuals tend to misbisect horizontal lines to the left of veridical centre. Nonetheless in virtually all previously reported studies on healthy participants, there have been subsets of people displaying rightward biases.</p> <p>In this study, we report differential time-on task effects depending on participants' initial pseudoneglect bias: participants with an initial left bias in a landmark task (in which they had to judge whether a transection mark appeared closer to the right or left end of a line) showed a significant rightward shift over the course of the experimental session, whereas participants with an initial right bias shifted leftwards.</p> <p>We argue that these differences in initial biases as well as the differential shifts with time-on task reflect genuine observer subtypes displaying diverging behavioural patterns. These observer subtypes could be driven by differences in brain organisation and/or lateralisation such as varying anatomical pathway asymmetries. </p&gt

The fusiform face area and occipital face area show sensitivity to spatial relations in faces

Behavioral research indicates that successful face individuation is associated with sensitivity to subtle spatial relations between facial features, as well as to the features themselves. We used a blocked functional magnetic resonance adaptation paradigm to examine the sensitivity of the core face network to spatial relations in faces. The fusiform face area (FFA) was sensitive to spatial relations, responding more strongly to a single face presented with various feature spacings than to repeated presentations of an identical face. This response to spacing variations was as strong as the response to a series of distinct identities. There were no hemisphere effects in sensitivity to spatial relations, although FFAs were larger on the right. The right occipital face area (OFA) was also sensitive to spatial relations in faces. Few participants showed left OFAs. The superior temporal sulcus (STS), which does not code identity, showed little sensitivity to either relational changes or changes in identity. We suggest that the sensitivity of the FFA and right OFA to spatial relations in faces may contribute to our impressive ability to individuate faces despite their similarity as visual patterns

Stimulus- and state-dependence of systematic bias in spatial attention: Additive effects of stimulus-size and time-on-task

Systematic biases in spatial attention are a common finding. In the general population, a systematic leftward bias is typically observed (pseudoneglect), possibly as a consequence of right hemisphere dominance for visuospatial attention. However, this leftward bias can cross-over to a systematic rightward bias with changes in stimulus and state factors (such as line length and arousal). The processes governing these changes are still unknown. Here we tested models of spatial attention as to their ability to account for these effects. To this end, we experimentally manipulated both stimulus and state factors, while healthy participants performed a computerized version of a landmark task. State was manipulated by time-on-task (>1 h) leading to increased fatigue and a reliable left- to rightward shift in spatial bias. Stimulus was manipulated by presenting either long or short lines which was associated with a shift of subjective midpoint from a reliable leftward bias for long to a more rightward bias for short lines. Importantly, we found time-on-task and line length effects to be additive suggesting a common denominator for line bisection across all conditions, which is in disagreement with models that assume that bisection decisions in long and short lines are governed by distinct processes (Magnitude estimation vs Global/local distinction). Our findings emphasize the dynamic rather than static nature of spatial biases in midline judgement. They are best captured by theories of spatial attention positing that spatial bias is flexibly modulated, and subject to inter-hemispheric balance which can change over time or conditions to accommodate task demands or reflect fatigue