79 research outputs found
Binocular functional architecture for detection of contrast-modulated gratings
No full textCombination of signals from the two eyes is the gateway to stereo vision. To gain insight into binocular signal processing, we studied binocular summation for luminance-modulated gratings (L or LM) and contrast-modulated gratings (CM). We measured 2AFC detection thresholds for a signal grating (0.75 c/deg, 216msec) shown to one eye, both eyes, or both eyes out-of-phase. For LM and CM, the carrier noise was in both eyes, even when the signal was monocular. Mean binocular thresholds for luminance gratings (L) were 5.4dB better than monocular thresholds - close to perfect linear summation (6dB). For LM and CM the binocular advantage was again 5-6dB, even when the carrier noise was uncorrelated, anti-correlated, or at orthogonal orientations in the two eyes. Binocular combination for CM probably arises from summation of envelope responses, and not from summation of these conflicting carrier patterns. Antiphase signals produced no binocular advantage, but thresholds were about 1-3dB higher than monocular ones. This is not consistent with simple linear summation, which should give complete cancellation and unmeasurably high thresholds. We propose a three-channel model in which noisy monocular responses to the envelope are binocularly combined in a contrast-weighted sum, but also remain separately available to perception via a max operator. Vision selects the largest of the three responses. With in-phase gratings the binocular channel dominates, but antiphase gratings cancel in the binocular channel and the monocular channels mediate detection. The small antiphase disadvantage might be explained by a subtle influence of background responses on binocular and monocular detection
Shading and texture:Separate information channels with a common adaptation mechanism?
No full textWe outline a scheme for the way in which early vision may handle information about shading (luminance modulation, LM) and texture (contrast modulation, CM). Previous work on the detection of gratings has found no sub-threshold summation, and no cross-adaptation, between LM and CM patterns. This strongly implied separate channels for the detection of LM and CM structure. However, we now report experiments in which adapting to LM (or CM) gratings creates tilt aftereffects of similar magnitude on both LM and CM test gratings, and reduces the perceived strength (modulation depth) of LM and CM gratings to a similar extent. This transfer of aftereffects between LM and CM might suggest a second stage of processing at which LM and CM information is integrated. The nature of this integration, however, is unclear and several simple predictions are not fulfilled. Firstly, one might expect the integration stage to lose identity information about whether the pattern was LM or CM. We show instead that the identity of barely detectable LM and CM patterns is not lost. Secondly, when LM and CM gratings are combined in-phase or out-of-phase we find no evidence for cancellation, nor for 'phase-blindness'. These results suggest that information about LM and CM is not pooled or merged - shading is not confused with texture variation. We suggest that LM and CM signals are carried by separate channels, but they share a common adaptation mechanism that accounts for the almost complete transfer of perceptual aftereffects
Sensitivity to contrast modulation: the spatial frequency dependence of second-order vision
No full textAbstractWe consider the overall shape of the second-order modulation sensitivity function (MSF). Because second-order modulations of local contrast or orientation require a carrier signal, it is necessary to evaluate modulation sensitivity against a variety of carriers before reaching a general conclusion about second-order sensitivity. Here we present second-order sensitivity functions for new carrier types (low pass (1/f) noise, and high pass noise) and demonstrate that, when first-order artefacts have been accounted for, the shape of the resulting MSFs are similar to one another and to those for white and broad band noise. They are all low pass with a likely upper frequency limit in the range 10–20 c/deg, suggesting that detection of second-order stimuli is relatively insensitive to the structure of the carrier signal. This result contrasts strongly with that found for (first-order) luminance modulations of the same noise types. Here the noise acts as mask and each noise type masks most those frequencies that are dominant in its spectrum. Thus the shape of second-order MSFs are largely independent of the spectrum of their noise carrier, but first-order CSFs depend on the spectrum of an additive noise mask. This provides further evidence for the separation of first- and second-order vision and characterises second-order vision as a low pass mechanism
Inflammatory markers in breast milk of HIV-infected and uninfected women in sub-Saharan African women.
No full textAt least 20% of women of reproductive age in parts of sub Saharan Africa are HIV-infected and transmission of HIV from mother-to-child through breastfeeding up to 2 years postpartum may account for half of the vertical transmission observed. However, little is known about factors within the breast that may influence milk viral load and/or transmission of HIV to the infant. The aim of this study was to explore the inflammatory processes that may affect the risk of mother-to-child transmission. This thesis was based on work from 4 different field studies: Rural Tanzania (n=85), urban South Africa (n=144), an urban hospital in Zambia (n=22) and an urban community in Zambia (n=112). Two of these studies were fully undertaken by the author (Zambian community and Zambian hospital studies) and two of the studies involved retrospective laboratory and statistical analysis by the author (Tanzanian study and South Africa study). The studies were designed to investigate the influence of social, biological and breastfeeding indicators on HIV status and severity of HIV infection in breastfeeding women. In addition, to determine if breast milk C-reactive protein (CRP) was a suitable surrogate measure for systemic inflammation and risk of mother-to-child transmission measured by non-invasive breast milk sampling. HIV infection in breastfeeding Zambian women was independently associated with raised breast milk CRP with an odds ratio (OR) of 3.91 (95% CI: 1.50, 10.17, p=0.005), giving birth to a male infant (OR=2.53; 95% CI: 1.38, 4.64; p 0.01) and greater maternal wealth (OR=1.12; 95% CI: 1.05, 1.22; p=0.001). Severity of HIV infection (women with a CD4 count at delivery of 500 cells/mm3 ) was independently associated with raised breast milk CRP (OR=2.49; 95% CI: 1.61, 3.87; p 0.001) and breast milk RNA (OR=1.28; 95% CI: 1.00, 1.63; p=0.05). Breast milk CRP was found to correlate with plasma CRP (rs>0.60; p 0.05) and breast milk IL-8 (rs 0.42; p 0.05); to be associated with poor infant feeding technique, poor feeding practice, maternal breast inflammation and reduced infant weight gain (p 0.05). Breast milk CRP was shown to positively correlate with breast milk RNA and inversely correlate with maternal CD4 count in South African women (p 0.05). Breast milk CRP has been shown to be associated with maternal HIV status and increased HIV severity in breastfeeding sub Saharan African women. Further work is needed to assess if CRP could be used as a surrogate risk factor for mother to child transmission of HIV
Equity fines for corporate crime: Why they should be back on the legislative agenda
No full text© The Author(s) 2019. Corporate crime causes significant social and environmental harm and its sentencing is frequently ineffective due to the ability of corporations to pass-on monetary fines to stakeholders such as workers and consumers. This article investigates the notion of equity fines or share dilution as an alternative corporate punishment that avoids the pitfalls of conventional monetary fines while acting as a significant deterrent to corporate offending. It does so by responding to the last official Australian critique of this punishment, in light of a 2010 attempt by the Scottish legislature to implement equity fines in that jurisdiction
Undoing a model system: A new federal custody notification service
No full text© The Author(s) 2018. The Custody Notification Service is a legislative scheme to prevent Aboriginal deaths in custody. This article discusses proposed changes to the federal Custody Notification Service, that were before the federal Parliament in late 2017. It argues that the changes are inadequate, when compared with Custody Notification Service models in other Australian jurisdictions, primarily because the laws deprive Aboriginal people of important fair trial and custody rights. This article concludes by listing a range of legislative solutions proposed by Aboriginal organisations and legal representatives
A survey of discharge planning for thirty paraplegics
No full textThesis (M.S.)--Boston UniversityPLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at [email protected]. Thank you.2999-01-0
Silence Matters: A survey of the right to silence in the summary jurisdiction of New South Wales
No full text© The Author(s) 2019. There is a scant existing literature on the relationship between the right to silence and its effect on convictions in Australia and comparable jurisdictions. Existing research has downplayed its significance in the face of various ‘law and order’ interventions seeking to limit its operation. This study is one of the largest of its kind, surveying over 1,000 charges to empirically assess the frequency of use and the effects of silence rights (the right to silence, privilege against self-incrimination and burden of proof) on conviction, in relation to a particular set of charges laid against a specific group of marginalised defendants in the Local Court summary jurisdiction of NSW. Adding to the existing literature, this study shows empirically how silence rights operate within an Australian summary jurisdiction for a specific group of criminal defendants who are significantly socially marginalised. In the process, it demonstrates that the use of silence rights is significant for this group, mostly in non-regulatory criminal matters. In this respect, silence rights can be understood to correlate with rates of conviction, mitigation of criminal sentencing and the practice of charge-bargaining
The temporal properties of first- and second-order vision
No full textAbstractVision is sensitive to first-order modulations of luminance and second-order modulations of image contrast. There is now a body of evidence that the two types of modulation are detected by separate mechanisms. Some previous experiments on motion detection have suggested that the second-order system is quite sluggish compared to the first-order system. Here we derive temporal properties of first- and second-order vision at threshold from studies of temporal integration and two-pulse summation. Three types of modulation were tested: luminance gratings alone, luminance modulations added to dynamic visual noise, and contrast modulations of dynamic noise. Data from the two-pulse summation experiment were used to derive impulse response functions for the three types of stimulus. These were then used to predict performance in the temporal integration experiment. Temporal frequency response functions were obtained as the Fourier transform of impulse responses derived from data averaged across two observers. The response to noise-free luminance gratings of 2 c/deg was bi-phasic and transient in the time domain, and bandpass in the frequency domain. The addition of dynamic noise caused the response to become mono-phasic, sustained and low-pass. The response to contrast modulated noise (second-order) was also mono-phasic, sustained and low-pass, with only a slightly longer integration time than in the first-order case. The ultimate roll-off at high frequencies was about the same as for the first-order case. We conclude that second-order vision may not be as sluggish as previously thought
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