Spatial selectivity in adaptation to gaze direction

A person's focus of attention is conveyed by the direction of their eyes and face, providing a simple visual cue fundamental to social interaction. A growing body of research examines the visual mechanisms that encode the direction of another person's gaze as we observe them. Here we investigate the spatial receptive field properties of these mechanisms, by testing the spatial selectivity of sensory adaptation to gaze direction. Human observers were adapted to faces with averted gaze presented in one visual hemifield, then tested in their perception of gaze direction for faces presented in the same or opposite hemifield. Adaptation caused strong, repulsive perceptual aftereffects, but only for faces presented in the same hemifield as the adapter. This occurred even though adapting and test stimuli were in the same external location across saccades. Hence, there was clear evidence for retinotopic adaptation and a relative lack of either spatiotopic or spatially invariant adaptation. These results indicate that adaptable representations of gaze direction in the human visual system have retinotopic spatial receptive fields. This strategy of coding others' direction of gaze with positional specificity relative to one's own eye position may facilitate key functions of gaze perception, such as socially cued shifts in visual attention

Gender and sexuality

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Gaze Behavior as a Visual Cue to Animacy

A characteristic that distinguishes biological agents from inanimate objects is that the former can have a direction of attention. While it is natural to associate a person’s direction of attention with the appearance of their face, attentional behaviors are also a kind of relational motion, in which an entity rotates a specific axis of its form in relation to an independent feature of its environment. Here, we investigated the role of gaze-like motion in providing a visual cue to animacy independent of the human form. We generated animations in which the rotation of a geometric object (the agent) was dependent on the movement of a target. Participants made judgements about how creature-like the objects appeared, which were highly sensitive to the correspondence between objects over and above their individual motion. We varied the dependence between agent rotation and target motion in terms of temporal synchrony, temporal order, cross-correlation, and trajectory complexity. These affected perceptions of animacy to differing extents. When the behavior of the agent was driven by a model of predictive tracking with a sensory sampling delay, perceived animacy was broadly tuned across changes in rotational behavior induced by the sampling delay of the agent. Overall, the tracking relationship provides a salient cue to animacy independent of biological form, provided that temporal synchrony between objects is within a certain range. This motion relationship may be one to which the visual system is highly attuned, due to its association with attentional behavior and the presence of other minds in our environment

Face detection from patterns of shading and shadows: The role of overhead illumination in generating the familiar appearance of the human face

Face detection in human vision relies on a stereotypical pattern of visual features common to different faces. How are these visual features generated in the environment? Here we investigate how characteristic patterns of shading and shadows that occur across the face act as a cue for face detection. We use 3D rendering to isolate facial shading under simulated lighting conditions, comparing the broad patterns of contrast that occur across the face when light arrives from different angles. We find that human performance in discriminating faces from non-face objects using these contrast patterns depends strongly on the lighting direction. In particular, light arriving from above the brow tends to facilitate face detection – consistent with the statistics of real-world lighting environments, in which light commonly arrives more strongly from above. Indeed, in a further experiment, we find that asymmetries in lighting that occur in complex and naturalistic lighting environments produce contrast patterns across the face that facilitate face detection. These effects occurred independent of the lighting direction relative to the viewer, suggesting that cues to face detection emerge from the interaction between face morphology and vertical asymmetries in lighting direction, independent of the viewer's knowledge or expectations about lighting direction. Comparison with the performance of an image classifier suggests that the effects of lighting direction partly reflect differences in image information that result from the interaction between shape and illumination, as well as face detection in human observers being better-tuned to the pattern of shading and shadows that occurs across an upright face that is lit from overhead

Is there a ‘zone of eye contact’ within the borders of the face?

Eye contact is a salient feature of everyday interactions, yet it is not obvious what the physical conditions are under which we feel that we have eye contact with another person. Here we measure the range of locations that gaze can fall on a person's face to elicit a sense of eye contact. Participants made judgements about eye contact while viewing rendered images of faces with finely-varying gaze direction at a close interpersonal distance (50 cm). The ‘zone of eye contact’ tends to peak between the two eyes and is often surprisingly narrower than the observer's actual eye region. Indeed, the zone tends to extend further across the face in height than in width. This shares an interesting parallel with the ‘cyclopean eye’ of visual perspective – our sense of looking out from a single point in space despite the physical separation of our two eyes. The distribution of eye-contact strength across the face can be modelled at the individual-subject level as a 2D Gaussian function. Perception of eye contact is more precise than the sense of having one's face looked at, which captures a wider range of gaze locations in both the horizontal and vertical dimensions, at least at the close viewing distance used in the present study. These features of eye-contact perception are very similar cross-culturally, tested here in Australian and Japanese university students. However, the shape and position of the zone of eye contact does vary depending on recent sensory experience: adaptation to faces with averted gaze causes a pronounced shift and widening of the zone across the face, and judgements about eye contact also show a positive serial dependence. Together, these results provide insight into the conditions under which eye contact is felt, with respect to face morphology, culture, and sensory context

Adaptation to Walking Direction in Biological Motion

The direction that we see another person walking provides us with an important cue to their intentions, but little is known about how the brain encodes walking direction across a neuronal population. The current study used an adaptation technique to investigate the sensory coding of perceived walking direction. We measured perceived walking direction of point-light stimuli before and after adaptation, and found that adaptation to a specific walking direction resulted in repulsive perceptual aftereffects. The magnitude of these aftereffects was tuned to the walking direction of the adaptor relative to the test, with local repulsion of perceived walking direction for test stimuli oriented on either side of the adapted walking direction. The specific tuning profiles that we observed are well explained by a population-coding model, in which perceived walking direction is coded in terms of the relative activity across a bank of sensory channels with peak tuning distributed across the full 360° range of walking directions. Further experiments showed specificity in how horizontal (azimuth) walking direction is coded when moving away from the observer compared to when moving toward the observer. Moreover, there was clear specificity in these perceptual aftereffects for walking direction compared to a nonbiological form of 3D motion (a rotating sphere). These results indicate the existence of neural mechanisms in the human visual system tuned to specific walking directions, provide insight into the number of sensory channels and how their responses are combined to encode walking direction, and demonstrate the specificity of adaptation to biological motion

sFlt-1 and NTproBNP independently predict mortality in a cohort of heart failure patients.

Objective: Soluble fms-like tyrosine kinase-1 (sFlt-1) is a circulating receptor for VEGF-A. Recent reports of elevated plasma levels of sFlt-1 in coronary heart disease and heart failure (HF) motivated our study aimed at investigating the utility of sFlt-1 as a prognostic biomarker in heart failure patients. Methods: ELISA assays for sFlt-1 and NTproBNP were performed in n=858 patients from a prospective multicentre, observational study (the PEOPLE study) of outcome among patients after appropriate treatment for an episode of acute decompensated HF in New Zealand. Plasma was sampled at a baseline visit and stored at -80°C. Statistical tests were adjusted for patient age at baseline visit, skewed data were log-adjusted and the endpoint for clinical outcome analysis was all-cause death. Patients were followed for a median of 3.63 (range 0.74-5.50) years. Results: Mean baseline plasma sFlt-1 was 125 +/- 2.01 pg/ml. sFlt-1 was higher in patients with HF with reduced ejection fraction (HFrEF) (130 +/- 2.62 pg/ml, n=553) compared to those with HF with preserved EF (HFpEF) (117 +/-3.59 pg/ml, n=305; p=0.005). sFlt-1 correlated with heart rate (r=0.148, p<0.001), systolic blood pressure (r=-0.139, p<0.001) and LVEF (r=-0.088, p=0.019). A Cox proportional hazards model showed sFlt-1 was a predictor of all-cause death (HR=6.30, p<0.001) in the PEOPLE cohort independent of age, NTproBNP, ischaemic aetiology, and NYHA class (n=842, 274 deaths), established predictors of mortality in the PEOPLE cohort. Conclusion: sFlt-1 levels at baseline should be investigated further as a predictor of death; complementary to established prognostic biomarkers in heart failure

Autistic adults show preserved normalisation of sensory responses in gaze processing

Progress in our understanding of autism spectrum disorder (ASD) has recently been sought by characterising how systematic differences in canonical neural computations employed across the sensory cortex might contribute to clinical symptoms in diverse sensory, cognitive, and social domains. A key proposal is that ASD is characterised by reduced divisive normalisation of sensory responses. This provides a bridge between genetic and molecular evidence for an increased ratio of cortical excitation to inhibition in ASD and the functional characteristics of sensory coding that are relevant for understanding perception and behaviour. Here we tested this hypothesis in the context of gaze processing (i.e., the perception of other people's direction of gaze), a domain with direct relevance to the core diagnostic features of ASD. We show that reduced divisive normalisation in gaze processing is associated with specific predictions regarding the psychophysical effects of sensory adaptation to gaze direction, and test these predictions in adults with ASD. We report compelling evidence that both divisive normalisation and sensory adaptation occur robustly in adults with ASD in the context of gaze processing. These results have important theoretical implications for defining the types of divisive computations that are likely to be intact or compromised in this condition (e.g., relating to local vs distal control of cortical gain). These results are also a strong testament to the typical sensory coding of gaze direction in ASD, despite the atypical responses to others' gaze that are a hallmark feature of this diagnosis.This research was supported by a Wellcome Trust Senior Clinical Research Fellowship (100227) awarded to GR and Australian Research Council Discovery Project (DP160102239) awarded to CC. This work was enabled partly by a study visit grant to CP from the Experimental Psychology Society. We thank all the participants who gave up their time to take part in this research

Opportunities for Process Control and Quality Assurance Using Online NIR Analysis to a Continuous Wet Granulation Tableting Line

This paper investigates the application of online near-infrared measurements as a means to measure blend uniformity in a continuous tableting line. Underlying all the monitoring and control methods is the ability to measure key tablet properties online at a rate suitable for control purposes. The use of NIR to determine any deviations in blend uniformity is demonstrated by interpreting the relevant spectral signature allowing quantitative information to be acquired for process monitoring and quality assurance. In addition to demonstrating the functionality of the NIR probe, the practical issues arising in the application are discussed. The composition of the blend was measured using an NIR probe over a range of concentrations and the results were calculated comparing sub unit dose scale of scrutiny of small populations. This was compared with predicted product quality for whole tablets over the whole production period. This technique has demonstrated how data collected online can be used to successfully predict the quality of the whole production run for the purposes of real-time product quality assurance

Transport J<inf>c</inf> in Bulk Superconductors: A Practical Approach?

The characterisation of the critical current density of bulk high temperature superconductors is typically performed using magnetometry, which involves numerous assumptions including, significantly, that Jc within the sample is uniform. Unfortunately, magnetometry is particularly challenging to apply where a local measurement of Jc across a feature, such as a grain boundary, is desired. Although transport measurements appear to be an attractive alternative to magnetization, it is extremely challenging to reduce the cross-sectional area of a bulk sample sufficiently to achieve a sufficiently low critical current that can be generated by a practical current source. In the work described here, we present a technique that enables transport measurements to be performed on sections of bulk superconductors. Metallographic techniques and resin reinforcement were used to create an I-shaped sample of bulk superconductor from a section of Gd-Ba-Cu-O containing 15 wt % Ag2O. The resulting superconducting track had a cross-sectional area of 0.44 mm2. The sample was found to support a critical current of 110 A using a field criterion in the narrowed track region of 1 μV cm-1. We conclude, therefore, that it is possible to measure critical current densities in excess of 2.5 x 108 A m-2 in sections of a bulk superconductor.This work was supported by the Engineering and Physical Sciences Research Council, via a Doctoral Training Award (grant number is EP/L504920/1) and funding from grant number EP/K02910X/1. This work was also supported by the Boeing Company. All data are provided in full in the results section of this paper.This is the author accepted manuscript. The final version is available from IEEE via http://dx.doi.org/10.1109/TASC.2016.253764