Scene representations conveyed by cortical feedback to early visual cortex can be described by line drawings

Human behavior is dependent on the ability of neuronal circuits to predict the outside world. Neuronal circuits in early visual areas make these predictions based on internal models that are delivered via non-feedforward connections. Despite our extensive knowledge of the feedforward sensory features that drive cortical neurons, we have a limited grasp on the structure of the brain's internal models. Progress in neuroscience therefore depends on our ability to replicate the models that the brain creates internally. Here we record human fMRI data while presenting partially occluded visual scenes. Visual occlusion allows us to experimentally control sensory input to subregions of visual cortex while internal models continue to influence activity in these regions. Since the observed activity is dependent on internal models, but not on sensory input, we have the opportunity to map visual features conveyed by the brain's internal models. Our results show that activity related to internal models in early visual cortex are more related to scene-specific features than to categorical or depth features. We further demonstrate that behavioral line drawings provide a good description of internal model structure representing scene-specific features. These findings extend our understanding of internal models, showing that line drawings provide a window into our brains' internal models of vision

Encoding and decoding of cortical feedback to human early visual cortex

Only 5% of excitatory input to primary visual cortical (V1) neurons corresponds to feedforward input from the retina, and only 20% of responses by these neurons can be explained by retinal input (Carandini, 2005; Muckli and Petro, 2013). Neuronal responses are therefore highly influenced by non-feedforward interactions, allowing the brain to combine external input from the retina with context and knowledge. This is accomplished by integrating feedforward input with signals from neurons processing higher-level or associative information. The signals transmitted from higher cortical areas to V1 are known as cortical feedback. The neuroscientific community is in agreement that cortical feedback is an important aspect of brain processing. However, the information transmitted by feedback and what factors give rise to contextual feedback remain largely unknown. Feedback connections provide V1 neurons with information about their far surround receptive fields (Angelucci and Bressloff, 2006), and stimulation in the surround provides contextual information about the scene to non-stimulated portions of V1 (Smith and Muckli, 2010; Muckli et al., 2015). Occluded V1 activity patterns recorded using fMRI have been used to decode different scenes, but again, little is known regarding the nature and content of the contextual information that feedback transmits. This thesis aims to examine the information in contextual feedback to early visual cortex, with a particular focus on V1. To investigate this topic we used an occlusion paradigm derived from that of Smith and Muckli (2010) and Muckli et al. (2015). During normal vision, both feedforward and feedback signals are present. As such, a useful approach to study feedback is to isolate it from feedforward input. We occluded one quadrant of the visual field during stimulus presentation in order to remove meaningful feedforward input about scenes in a portion of retinotopic visual cortex. We used fMRI to assess brain activity in early visual cortex, allowing us to detect dendritic signaling associated with cortical feedback due to its sensitivity to cortical energy consumption (Logothetis, 2007, 2008; Petro et al., 2014). In Chapter 2, we investigated potential high-level information in cortical feedback to V1 and V2. We presented subjects with an expanded version of the occlusion paradigm from Smith and Muckli (2010) and Muckli et al. (2015). We included twenty-four partially occluded scenes from six categories and spatial depths. These two high-level scene characteristics were chosen because they have previously been shown to modulate early visual cortical responses (Walther et al., 2009; Kravitz et al., 2011). We were therefore interested in whether these characteristics also modulate feedback to V1 and V2. We found that response patterns in these subregions contain high-level category information, but we did not find that visual depth information generalized across exemplars. Additionally, we found that retinotopic responses in Occluded V1 and V2 differed from each other, suggesting that feedback to these two areas has different information content, and matching the known anatomical connections from mid- and higher-level visual areas in the ventral stream (Rockland et al., 1994; Rockland and Ojima, 2003). In Chapter 3, we probed the information content of Occluded V1 and V2 responses at multiple levels of complexity using Representational Similarity Analysis (RSA) and encoding models. By analyzing data from Chapter 2 in these frameworks, we were able to compare both local (voxelwise) and distributed (multi-voxel) Occluded responses to three biologically-inspired computational models (the contrast energy-based Weibull model, the orientation-based Gist model, and the mid-level vision H-Max model), and the high-level scene characteristics explored in Chapter 2. Using RSA, we also compared scene representations from Occluded and Non-Occluded areas. We found that in Non-Occluded areas, V1 and V2 represent scenes similarly, while Occluded V1 and V2 do not. We also found that scene representations in Occluded V1 and V2 were correlated with high-level Category and H-Max models. Individual voxel encoding models showed that Occluded V1 voxels within 5◦ visual angle of fixation encode low-level information about the occluded scene, while voxels outside of 5◦ encode higher-level information. These results highlight a potential visual field bias in the type of information transmitted to V1 through feedback, with foveal voxels receiving more precise, low-level scene information, and peripheral voxels receiving more invariant or global scene features. In Chapter 4, we examined the laminar profile of Occluded V1 using high-resolution (0.8mm3) 7T fMRI. We again expanded our stimulus set, now with 192 Occluded scenes and 192 Non-Occluded scenes. This large stimulus set allowed us to map scene information onto voxel responses in greater detail, and the use of both Occluded and Non-Occluded scenes allowed us to compare voxel responses when receiving only feedback with responses when receiving feedforward, lateral and feedback information. We found that V1 responses exhibit predictive and high-level response properties in addition to feedforward orientation and spatial frequency properties typically associated with V1 responses. These predictive and high-level responses were primarily associated with superficial layers of cortex. We also found that voxel tuning toward feedforward and feedback signals was different between cortical layers of V1. Our findings suggest that feedback connections terminating in superficial layers provide V1 neurons with contextual and associative information not available via localized feedforward input. The neuroscientific results presented in this thesis extend our knowledge about the information content of cortical feedback to early visual cortex. These results add support to the notion that V1 can be considered to speak two languages (Muckli and Petro, 2013). Not only does it play a role as an early stage of processing of sensory visual input, where it deals with processing low-level features, but it also receives messages from diverse areas of cortex and these messages supplement local processing by providing contextual information

Public Health Outcomes as a Measure of Efficacy of Syringe Exchange Programs

Introduction. A syringe exchange is a public health intervention that offers nonjudgmental services to intravenous drug users (IVDU), providing clean syringes in exchange for used syringes. While prior studies demonstrated that syringe exchanges can reduce transmission of HIV, hepatitis C, and other blood-borne pathogens, other measures of health improvements have been less studied. Methods. 91 members of Vermont CARES syringe exchange program were surveyed on their healthcare practices. New members were defined asprogram. Results. Long-term members tended to have a primary care provider (PCP). Lack of insurance and fear of judgment were commonly cited reasons for not having a PCP. Long-term members were significantly less likely (p=0.04) to use costly emergency department (ED) services and less likely to reuse their own or another person\u27s needles. Long-term members were more likely to be in addiction treatment and reported a greater desire to abstain from drug use. New members were more likely to obtain hepatitis C and HIV testing in the past year. Discussion. Subjects responded positively to the possibility of accessing PCP services through VT CARES, offering a continuation of the nonjudgmental healthcare environment. Decreased ED visits significantly correlated with longer membership, reflecting the positive impact of the syringe exchange education services on reducing healthcare costs. Decreased testing among long-term members may reflect prior knowledge of their status. Long-term members were less likely to reuse their own needles or ones used by another person, suggesting the distribution of clean syringes encourages safer injection practices.https://scholarworks.uvm.edu/comphp_gallery/1247/thumbnail.jp

Inferring the age and sex of ancient potters from fingerprint ridge densities: A data-driven, Bayesian mixture modelling approach

The density of epidermal ridges in a fingerprint varies predictably by age and sex. Archaeologists are therefore interested in using recovered fingerprints to learn about the ancient people who produced them. Recent studies focus on estimating the age and sex of individuals by measuring their fingerprints with one of two similar metrics: mean ridge breadth (MRB) or ridge density (RD). Yet these attempts face several critical problems: expected values for adult females and adolescent males are inherently indistinguishable, and inter-assemblage variation caused by biological and technological differences cannot be easily estimated. Each of these factors greatly decreases the accuracy of predictions based on individual prints, and together they condemn this strategy to relative uselessness. However, information in fingerprints from across an assemblage can be pooled to generate a more accurate depiction of potter demographics. We present a new approach to epidermal ridge density analysis using Bayesian mixture models with the following key benefits: Age and sex are estimated more accurately than existing methods by incorporating a data-driven understanding of how demographics and ridge density covary. Uncertainty in demographic estimates is automatically quantified and included in output. The Bayesian framework can be easily adapted to fit the unique needs of different researchers. </p

Assessment of health in human faces is context-dependent

This work was supported by the National Environment Research Council, UK (KM), Unilever Research & Development USA and the Economic and Social Research Council (RW, DP).When making decisions between options, humans are expected to choose the option that returns the highest benefit. In practice, however, adding inferior alternatives to the choice set can alter these decisions. Here we investigated whether decisions over the facial features that people find healthy looking can also be affected by the context in which they see those faces. To do this we examined the effect of choice set on the perception of health of images of faces of light-skinned Caucasian females. We manipulated apparent facial health by changing yellowness of the skin: the healthy faces were moderately yellow and the less healthy faces were either much more yellow or much less yellow. In each experiment, two healthy faces were presented along with a third, less healthy face. When the third face was much more yellow, participants chose the more yellow of the two healthy faces more often as the most healthy. However, when the third face was the least yellow, participants chose the less yellow of the two healthy faces more often. A further experiment confirmed that this result is not due to a generalised preference for an intermediate option. These results extend our understanding of context-dependent decision-making in humans, and suggest that comparative evaluation may be a common feature across many different kinds of choices that humans have to make.PostprintPeer reviewe

The Relationship of Field Burn Severity Measures To Satellite-derived Burned Area Reflectance Classification (Barc) Maps

Preliminary results are presented from ongoing research on spatial variability of fire effects on soils and vegetation from the Black Mountain Two and Cooney Ridge wildfires, which burned in western Montana during the 2003 fire season. Extensive field fractional cover data were sampled to assess the efficacy of quantitative satellite image-derived indicators of burn severity. The objective of this study was to compare the field burn severity measures to the digital numbers used to produce Burned Area Reflectance Classification (BARC) maps. Canopy density was the field variable most highly correlated to BARC data derived from either SPOT Multispectral (XS) or Landsat Thematic Mapper (TM) imagery. Among the other field variables, old litter depth and duff depth correlated better with the satellite data than did old litter cover. Ash cover correlated most poorly. Old litter cover correlated better with the satellite data than did exposed mineral soil or rock cover, but combining the mineral soil and rock cover fractions into a single inorganic cover fraction improved the correlation to a comparable level. Most field variables, with the notable exception of ash, tended to vary more at low and moderate severity sites than at high severity sites. Semivariograms of the field variables revealed spatial autocorrelation across the spatial scales sampled (2 – 130 m), which the 20 m or 30 m resolution satellite imagery only weakly detected. Future analyses will be broadened to quantify burn severity characteristics in other forest types and to consider erosion processes, such as soil water infiltration following fire

Evaluating Aster Satellite Imagery And Gradient Modeling For Mapping And Characterizing Wildland Fire Fuels

Land managers need cost-effective methods for mapping and characterizing fire fuels quickly and accurately. The advent of sensors with increased spatial resolution may improve the accuracy and reduce the cost of fuels mapping. The objective of this research is to evaluate the accuracy and utility of imagery from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite and gradient modeling for mapping fuel layers for fire behavior modeling within FARSITE. An empirical model, based upon field data and spectral information from an ASTER image, was employed to test the efficacy of ASTER for mapping and characterizing canopy closure and crown bulk density. Surface fuel models (NFFL 1-13) were mapped using a classification tree based upon three gradient layers; potential vegetation type, cover type, and structural stage

The Relationship of Field Burn Severity Measures To Satellite-derived Burned Area Reflectance Classification (Barc) Maps

Preliminary results are presented from ongoing research on spatial variability of fire effects on soils and vegetation from the Black Mountain Two and Cooney Ridge wildfires, which burned in western Montana during the 2003 fire season. Extensive field fractional cover data were sampled to assess the efficacy of quantitative satellite image-derived indicators of burn severity. The objective of this study was to compare the field burn severity measures to the digital numbers used to produce Burned Area Reflectance Classification (BARC) maps. Canopy density was the field variable most highly correlated to BARC data derived from either SPOT Multispectral (XS) or Landsat Thematic Mapper (TM) imagery. Among the other field variables, old litter depth and duff depth correlated better with the satellite data than did old litter cover. Ash cover correlated most poorly. Old litter cover correlated better with the satellite data than did exposed mineral soil or rock cover, but combining the mineral soil and rock cover fractions into a single inorganic cover fraction improved the correlation to a comparable level. Most field variables, with the notable exception of ash, tended to vary more at low and moderate severity sites than at high severity sites. Semivariograms of the field variables revealed spatial autocorrelation across the spatial scales sampled (2 – 130 m), which the 20 m or 30 m resolution satellite imagery only weakly detected. Future analyses will be broadened to quantify burn severity characteristics in other forest types and to consider erosion processes, such as soil water infiltration following fire

Naval History by Conspiracy Theory: The British Admiralty before the First World War and the Methodology of Revisionism

Revisionist interpretations of British naval policy in the Fisher era claim that an elaborate smoke screen was created to hide the Royal Navy’s real policies; while documents showing the true goals were systematically destroyed. By asserting this, revisionists are able to dismiss those parts of the documentary record that contradict their theories, while simultaneously excusing the lack of evidence for their theories by claiming it has been destroyed. This article shows that this methodology is misleading and untenable

Assessment of genetic structure among Australian east coast populations of snapper Chrysophrys auratus (Sparidae)

Snapper Chrysophrys auratus is a high-value food fish in Australia targeted by both commercial and recreational fisheries. Along the east coast of Australia, fisheries are managed under four state jurisdictions (Queensland, Qld; New South Wales, NSW; Victoria, Vic.; and Tasmania, Tas.), each applying different regulations, although it is thought that the fisheries target the same biological stock. An allozyme-based study in the mid-1990s identified a weak genetic disjunction north of Sydney (NSW) questioning the single-stock hypothesis. This study, focused on east-coast C. auratus, used nine microsatellite markers to assess the validity of the allozyme break and investigated whether genetic structure exists further south. Nine locations were sampled spanning four states and over 2000 km, including sites north and south of the proposed allozyme disjunction. Analyses confirmed the presence of two distinct biological stocks along the east coast, with a region of genetic overlap around Eden in southern NSW, ~400 km south of the allozyme disjunction. The findings indicate that C. auratus off Vic. and Tas. are distinct from those in Qld and NSW. For the purpose of stock assessment and management, the results indicate that Qld and NSW fisheries are targeting a single biological stock.