The Brightness of Colour

Background: The perception of brightness depends on spatial context: the same stimulus can appear light or dark depending on what surrounds it. A less well-known but equally important contextual phenomenon is that the colour of a stimulus can also alter its brightness. Specifically, stimuli that are more saturated (i.e. purer in colour) appear brighter than stimuli that are less saturated at the same luminance. Similarly, stimuli that are red or blue appear brighter than equiluminant yellow and green stimuli. This non-linear relationship between stimulus intensity and brightness, called the Helmholtz-Kohlrausch (HK) effect, was first described in the nineteenth century but has never been explained. Here, we take advantage of the relative simplicity of this 'illusion' to explain it and contextual effects more generally, by using a simple Bayesian ideal observer model of the human visual ecology. We also use fMRI brain scans to identify the neural correlates of brightness without changing the spatial context of the stimulus, which has complicated the interpretation of related fMRI studies.Results: Rather than modelling human vision directly, we use a Bayesian ideal observer to model human visual ecology. We show that the HK effect is a result of encoding the non-linear statistical relationship between retinal images and natural scenes that would have been experienced by the human visual system in the past. We further show that the complexity of this relationship is due to the response functions of the cone photoreceptors, which themselves are thought to represent an efficient solution to encoding the statistics of images. Finally, we show that the locus of the response to the relationship between images and scenes lies in the primary visual cortex (V1), if not earlier in the visual system, since the brightness of colours (as opposed to their luminance) accords with activity in V1 as measured with fMRI.Conclusions: The data suggest that perceptions of brightness represent a robust visual response to the likely sources of stimuli, as determined, in this instance, by the known statistical relationship between scenes and their retinal responses. While the responses of the early visual system (receptors in this case) may represent specifically the statistics of images, post receptor responses are more likely represent the statistical relationship between images and scenes. A corollary of this suggestion is that the visual cortex is adapted to relate the retinal image to behaviour given the statistics of its past interactions with the sources of retinal images: the visual cortex is adapted to the signals it receives from the eyes, and not directly to the world beyond

Past Achievements and Future Challenges in 3D Photonic Metamaterials

Photonic metamaterials are man-made structures composed of tailored micro- or nanostructured metallo-dielectric sub-wavelength building blocks that are densely packed into an effective material. This deceptively simple, yet powerful, truly revolutionary concept allows for achieving novel, unusual, and sometimes even unheard-of optical properties, such as magnetism at optical frequencies, negative refractive indices, large positive refractive indices, zero reflection via impedance matching, perfect absorption, giant circular dichroism, or enhanced nonlinear optical properties. Possible applications of metamaterials comprise ultrahigh-resolution imaging systems, compact polarization optics, and cloaking devices. This review describes the experimental progress recently made fabricating three-dimensional metamaterial structures and discusses some remaining future challenges

A survey of assistive technologies and applications for blind users on mobile platforms: a review and foundation for research

This paper summarizes recent developments in audio and tactile feedback based assistive technologies targeting the blind community. Current technology allows applications to be efficiently distributed and run on mobile and handheld devices, even in cases where computational requirements are significant. As a result, electronic travel aids, navigational assistance modules, text-to-speech applications, as well as virtual audio displays which combine audio with haptic channels are becoming integrated into standard mobile devices. This trend, combined with the appearance of increasingly user- friendly interfaces and modes of interaction has opened a variety of new perspectives for the rehabilitation and training of users with visual impairments. The goal of this paper is to provide an overview of these developments based on recent advances in basic research and application development. Using this overview as a foundation, an agenda is outlined for future research in mobile interaction design with respect to users with special needs, as well as ultimately in relation to sensor-bridging applications in genera

Effects of PREPARE, a Multi-component, School-Based HIV and Intimate Partner Violence (IPV) Prevention Programme on Adolescent Sexual Risk Behaviour and IPV : Cluster Randomised Controlled Trial

Young South Africans, especially women, are at high risk of HIV. We evaluated the effects of PREPARE, a multi-component, school-based HIV prevention intervention to delay sexual debut, increase condom use and decrease intimate partner violence (IPV) among young adolescents. We conducted a cluster RCT among Grade eights in 42 high schools. The intervention comprised education sessions, a school health service and a school sexual violence prevention programme. Participants completed questionnaires at baseline, 6 and 12 months. Regression was undertaken to provide ORs or coefficients adjusted for clustering. Of 6244 sampled adolescents, 55.3 % participated. At 12 months there were no differences between intervention and control arms in sexual risk behaviours. Participants in the intervention arm were less likely to report IPV victimisation (35.1 vs. 40.9 %; OR 0.77, 95 % CI 0.61-0.99; t(40) = 2.14) suggesting the intervention shaped intimate partnerships into safer ones, potentially lowering the risk for HIV

Social and Structural Factors Associated with HIV Infection among Female Sex Workers Who Inject Drugs in the Mexico-US Border Region

BACKGROUND: FSWs who inject drugs (FSW-IDUs) can acquire HIV through high risk sexual and injection behaviors. We studied correlates of HIV infection among FSW-IDUs in northern Mexico, where sex work is quasi-legal and syringes can be legally obtained without a prescription. METHODS: FSW-IDUs>18 years old who reported injecting drugs and recent unprotected sex with clients in Tijuana and Ciudad Juarez underwent surveys and HIV/STI testing. Logistic regression identified correlates of HIV infection. RESULTS: Of 620 FSW-IDUs, prevalence of HIV, gonorrhea, Chlamydia, trichomonas, syphilis titers ≥1:8, or any of these infections was 5.3%, 4%, 13%, 35%, 10% and 72%, respectively. Compared to other FSW-IDUs, HIV-positive women were more likely to: have syphilis titers ≥1:8 (36% vs. 9%, p<0.001), often/always inject drugs with clients (55% vs. 32%, p = 0.01), and experience confiscation of syringes by police (49% vs. 28%, p = 0.02). Factors independently associated with HIV infection were syphilis titers ≥1:8, often/always injecting with clients and police confiscation of syringes. Women who obtained syringes from NEPs (needle exchange programs) within the last month had lower odds of HIV infection associated with active syphilis, but among non-NEP attenders, the odds of HIV infection associated with active syphilis was significantly elevated. CONCLUSIONS: Factors operating in both the micro-social environment (i.e., injecting drugs with clients) and policy environment (i.e., having syringes confiscated by police, attending NEPs) predominated as factors associated with risk of HIV infection, rather than individual-level risk behaviors. Interventions should target unjustified policing practices, clients' risk behaviors and HIV/STI prevention through NEPs

Design of a Trichromatic Cone Array

Cones with peak sensitivity to light at long (L), medium (M) and short (S) wavelengths are unequal in number on the human retina: S cones are rare (<10%) while increasing in fraction from center to periphery, and the L/M cone proportions are highly variable between individuals. What optical properties of the eye, and statistical properties of natural scenes, might drive this organization? We found that the spatial-chromatic structure of natural scenes was largely symmetric between the L, M and S sensitivity bands. Given this symmetry, short wavelength attenuation by ocular media gave L/M cones a modest signal-to-noise advantage, which was amplified, especially in the denser central retina, by long-wavelength accommodation of the lens. Meanwhile, total information represented by the cone mosaic remained relatively insensitive to L/M proportions. Thus, the observed cone array design along with a long-wavelength accommodated lens provides a selective advantage: it is maximally informative

Prevention interventions for human immunodeficiency virus in drug-using women with a history of partner violence

Jamila K Stockman1, Natasha Ludwig-Barron1, Monica A Hoffman2, Monica D Ulibarri3, Typhanye V Penniman Dyer41Division of Global Public Health, Department of Medicine; 2Department of Communication and Science Studies; 3Department of Psychiatry, University of California, San Diego, La Jolla, CA; 4Department of Epidemiology and Biostatistics, University of Maryland School of Public Health, College Park, MD, USAAbstract: The intersecting epidemics of human immunodeficiency virus (HIV) and partner violence disproportionately affect women who use drugs. Despite accumulating evidence throughout the world linking these epidemics, HIV prevention efforts focused on these synergistic issues as well as underlying determinants that contribute to the HIV risk environment (eg, housing instability, incarceration, policing practices, survival sex) are lacking. This article highlights selected behavior change theories and biomedical approaches that have been used or could be applied in HIV prevention interventions for drug-using women with histories of partner violence and in existing HIV prevention interventions for drug-using women that have been gender-focused while integrating histories of partner violence and/or relationship power dynamics. To date, there is a paucity of HIV prevention interventions designed for drug-using women (both in and outside of drug treatment programs) with histories of partner violence. Of the few that exist, they have been theory-driven, culture-specific, and address certain aspects of gender-based inequalities (eg, gender-specific norms, relationship power and control, partner violence through assessment of personal risk and safety planning). However, no single intervention has addressed all of these issues. Moreover, HIV prevention interventions for drug-using women with histories of partner violence are not widespread and do not address multiple components of the risk environment. Efficacious interventions should target individuals, men, couples, and social networks. There is also a critical need for the development of culturally tailored combination HIV prevention interventions that not only incorporate evidence-based behavioral and biomedical approaches (eg, microbicides, pre-exposure prophylaxis, female-initiated barrier methods) but also take into account the risk environment at the physical, social, economic and political levels. Ultimately, this approach will have a significant impact on reducing HIV infections among drug-using women with histories of partner violence.Keywords: human immunodeficiency virus, acquired immune deficiency syndrome, interventions, drugs, women, partner violence, gender-based inequalitie

Adverse pregnancy outcomes and sexual violence among female sex workers who inject drugs on the United States-Mexico border.

This study examines the prevalence of miscarriage/stillbirth among female sex workers who inject drugs (FSW-IDUs) and measures its associations with physical and sexual violence. Baseline data from 582 FSW-IDUs enrolled in an HIV intervention study in Tijuana and Ciudad Juárez, Mexico were used for current analyses. 30% of participants had experienced at least one miscarriage/stillbirth, 51% had experienced sexual violence, and 49% had experienced physical violence. History of miscarriage/stillbirth was associated with sexual violence (adjusted odds ratio [aOR] = 1.7, p = .02) but not physical violence. Additional reproductive risks associated with miscarriage/stillbirth included high numbers of male clients in the previous month (aOR = 1.1 per 30 clients, p = 0.04), history of abortion (aOR = 3.7, p &lt; .001), and higher number of pregnancies (aOR = 1.4 per additional pregnancy, p &lt; .001). Programs and research with this population should integrate reproductive health and consider gender-based violence