A new method for mapping perceptual biases across visual space

How we perceive the environment is not stable and seamless. Recent studies found that how a person qualitatively experiences even simple visual stimuli varies dramatically across different locations in the visual field. Here we use a method we developed recently that we call multiple alternatives perceptual search (MAPS) for efficiently mapping such perceptual biases across several locations. This procedure reliably quantifies the spatial pattern of perceptual biases and also of uncertainty and choice. We show that these measurements are strongly correlated with those from traditional psychophysical methods and that exogenous attention can skew biases without affecting overall task performance. Taken together, MAPS is an efficient method to measure how an individual's perceptual experience varies across space

Spatial Heterogeneity in Bistable Figure-Ground Perception

The appearance of visual objects varies substantially across the visual field. Could such spatial heterogeneity be due to undersampling of the visual field by neurons selective for stimulus categories? Here, we show that which parts of a bistable vase-face image observers perceive as figure and ground depends on the retinal location where the image appears. The spatial patterns of these perceptual biases were similar regardless of whether the images were upright or inverted. Undersampling by neurons tuned to an object class (e.g., faces) or variability in general local versus global processing cannot readily explain this spatial heterogeneity. Rather, these biases could result from idiosyncrasies in low-level sensitivity across the visual field

Population receptive field estimates for motion-defined stimuli

The processing of motion changes throughout the visual hierarchy, from spatially restricted ‘local motion’ in early visual cortex to more complex large-field ‘global motion’ at later stages. Here we used functional magnetic resonance imaging (fMRI) to examine spatially selective responses in these areas related to the processing of random-dot stimuli defined by differences in motion. We used population receptive field (pRF) analyses to map retinotopic cortex using bar stimuli comprising coherently moving dots. In the first experiment, we used three separate background conditions: no background dots (dot-defined bar-only), dots moving coherently in the opposite direction to the bar (kinetic boundary) and dots moving incoherently in random directions (global motion). Clear retinotopic maps were obtained for the bar-only and kinetic-boundary conditions across visual areas V1-V3 and in higher dorsal areas. For the global-motion condition, retinotopic maps were much weaker in early areas and became clear only in higher areas, consistent with the emergence of global-motion processing throughout the visual hierarchy. However, in a second experiment we demonstrate that this pattern is not specific to motion-defined stimuli, with very similar results for a transparent-motion stimulus and a bar defined by a static low-level property (dot size) that should have driven responses particularly in V1. We further exclude explanations based on stimulus visibility by demonstrating that the observed differences in pRF properties do not follow the ability of observers to localise or attend to these bar elements. Rather, our findings indicate that dorsal extrastriate retinotopic maps may primarily be determined by the visibility of the neural responses to the bar relative to the background response (i.e. neural signal-to-noise ratios) and suggests that claims about stimulus selectivity from pRF experiments must be interpreted with caution

Heritable functional architecture in human visual cortex

How much of the functional organization of our visual system is inherited? Here we tested the heritability of retinotopic maps in human visual cortex using functional magnetic resonance imaging. We demonstrate that retinotopic organization shows a closer correspondence in monozygotic (MZ) compared to dizygotic (DZ) twin pairs, suggesting a partial genetic determination. Using population receptive field (pRF) analysis to examine the preferred spatial location and selectivity of these neuronal populations, we estimate a heritability around 10–20% for polar angle preferences and spatial selectivity, as quantified by pRF size, in extrastriate areas V2 and V3. Our findings are consistent with heritability in both the macroscopic arrangement of visual regions and stimulus tuning properties of visual cortex. This could constitute a neural substrate for variations in a range of perceptual effects, which themselves have been found to be at least partially genetically determined. These findings also add convergent evidence for the hypothesis that functional map topology is linked with cortical morphology

The optimal experimental design for multiple alternatives perceptual search

Perceptual bias is inherent to all our senses, particularly in the form of visual illusions and aftereffects. However, many experiments measuring perceptual biases may be susceptible to nonperceptual factors, such as response bias and decision criteria. Here, we quantify how robust multiple alternative perceptual search (MAPS) is for disentangling estimates of perceptual biases from these confounding factors. First, our results show that while there are considerable response biases in our four-alternative forced-choice design, these are unrelated to perceptual biases estimates, and these response biases are not produced by the response modality (keyboard vs. mouse). We also show that perceptual bias estimates are reduced when feedback is given on each trial, likely due to feedback enabling observers to partially (and actively) correct for perceptual biases. However, this does not impact the reliability with which MAPS detects the presence of perceptual biases. Finally, our results show that MAPS can detect actual perceptual biases and is not a decisional bias towards choosing the target in the middle of the candidate stimulus distribution. In summary, researchers conducting a MAPS experiment should use a constant reference stimulus, but consider varying the mean of the candidate distribution. Ideally, they should not employ trial-wise feedback if the magnitude of perceptual biases is of interest

Microwave backscatter enhancement using radial anisotropy in biomimetic core-shell spheres

This is the final version. Available on open access from the American Institute of Physics via the DOI in this record.Data availability: The data that support the findings of this study are available from the corresponding authors upon reasonable request.Enhanced backscattering of microwave radiation is demonstrated experimentally in a biomimetic radially anisotropic spherical metamaterial component. The core-shell device replicates the optical function of nanospheres observed in the tapetum reflector of the compound eye of the shrimp Litopenaeus vannamei (Boone, 1931) and translates the effect from the optical domain to microwave frequencies. Analytical Mie theory calculations and numerical-method simulations are used to describe the origin of the observed scattering from a single dielectric sphere in terms of its multipolar Mie resonances. The fabrication of components using additive manufacture and their experimental characterization are described. The results show that the introduction of radial anisotropy in the shell more than doubles the monostatic radar cross section compared to the equivalent isotropic case. This work represents a practical demonstration of a synthetic bio-inspired structure, harnessing performance-enhancing adaptations that have evolved in nature. The results augment the range of techniques available for the control of electromagnetic scattering with relevance to applications in the manipulation of radar return signals.Engineering and Physical Sciences Research Council (EPSRC)Royal Academy of Engineerin

Crystal sedimentation and stone formation

Mechanisms of crystal collision being the first step of aggregation (AGN) were analyzed for calcium oxalate monohydrate (COM) directly produced in urine. COM was produced by oxalate titration in urine of seven healthy men, in solutions of urinary macromolecules and in buffered distilled water (control). Crystal formation and sedimentation were followed by a spectrophotometer and analyzed by scanning electron microscopy. Viscosity of urine was measured at 37°C. From results, sedimentation rate (vS), particle diffusion (D) and incidences of collision of particles in suspension by sedimentation (IS) and by diffusion (ID) were calculated. Calculations were related to average volume and urinary transit time of renal collecting ducts (CD) and of renal pelvis. vS was in urine 0.026 ± 0.012, in UMS 0.022 ± 0.01 and in control 0.091 ± 0.02 cm min−1 (mean ± SD). For urine, a D of 9.53 ± 0.97 μm within 1 min can be calculated. At maximal crystal concentration, IS was only 0.12 and ID was 0.48 min−1 cm−3 which, even at an unrealistic permanent and maximal crystalluria, would only correspond to less than one crystal collision/week/CD, whereas to the same tubular wall being in horizontal position 1.3 crystals/min and to a renal stone 624 crystals/cm2 min could drop by sedimentation. Sedimentation to renal tubular or pelvic wall, where crystals can accumulate and meet with a tissue calcification or a stone, is probably essential for stone formation. Since vS mainly depends on particle size, reducing urinary supersaturation and crystal growth by dietary oxalate restriction seems to be an important measure to prevent aggregation

Why do women not use antenatal services in low and middle income countries? A metasynthesis of qualitative studies

Background: Almost 50% of women in low & middle income countries (LMIC’s) don’t receive adequate antenatal care. Women’s views can offer important insights into this problem. Qualitative studies exploring inadequate use of antenatal services have been undertaken in a range of countries, but the findings are not easily transferable. We aimed to inform the development of future antenatal care programmes through a synthesis of findings in all relevant qualitative studies. Methods and Findings: Using a pre-determined search strategy, we identified robust qualitative studies reporting on the views and experiences of women in LMIC’s who received inadequate antenatal care. We used meta-ethnographic techniques to generate themes and a line of argument synthesis. We derived policy relevant hypotheses from the findings. We included 21 papers representing the views of more than 1230 women from 15 countries. Three key themes were identified: ‘Pregnancy as socially risky and physiologically healthy’; ‘Resource use and survival in conditions of extreme poverty’and ‘Not getting it right first time’. The line of argument synthesis describes a dissonance between programme design and cultural contexts that may restrict access and discourage return visits. We hypothesize that centralized, risk-focused antenatal care programmes may be at odds with the resources, beliefs and experiences of pregnant women who underuse antenatal services. Conclusions: Our findings suggest that there may be a mis-alignment between current antenatal provision and the social and cultural context of some women in LMIC’s. Antenatal care provision that is theoretically and contextually at odds with local contextual beliefs and experiences are likely to be underused, especially when attendance generates increased personal risks of lost family resource or physical danger during travel; when the promised care is not delivered due to resource constraints; and when women experience covert or overt abuse in care settings

Identifying priorities in methodological research using ICD-9-CM and ICD-10 administrative data: report from an international consortium

BACKGROUND: Health administrative data are frequently used for health services and population health research. Comparative research using these data has been facilitated by the use of a standard system for coding diagnoses, the International Classification of Diseases (ICD). Research using the data must deal with data quality and validity limitations which arise because the data are not created for research purposes. This paper presents a list of high-priority methodological areas for researchers using health administrative data. METHODS: A group of researchers and users of health administrative data from Canada, the United States, Switzerland, Australia, China and the United Kingdom came together in June 2005 in Banff, Canada to discuss and identify high-priority methodological research areas. The generation of ideas for research focussed not only on matters relating to the use of administrative data in health services and population health research, but also on the challenges created in transitioning from ICD-9 to ICD-10. After the brain-storming session, voting took place to rank-order the suggested projects. Participants were asked to rate the importance of each project from 1 (low priority) to 10 (high priority). Average ranks were computed to prioritise the projects. RESULTS: Thirteen potential areas of research were identified, some of which represented preparatory work rather than research per se. The three most highly ranked priorities were the documentation of data fields in each country's hospital administrative data (average score 8.4), the translation of patient safety indicators from ICD-9 to ICD-10 (average score 8.0), and the development and validation of algorithms to verify the logic and internal consistency of coding in hospital abstract data (average score 7.0). CONCLUSION: The group discussions resulted in a list of expert views on critical international priorities for future methodological research relating to health administrative data. The consortium's members welcome contacts from investigators involved in research using health administrative data, especially in cross-jurisdictional collaborative studies or in studies that illustrate the application of ICD-10