Intersession reliability of population receptive field estimates

Population receptive field (pRF) analysis is a popular method to infer spatial selectivity of voxels in visual cortex. However, it remains largely untested how stable pRF estimates are over time. Here we measured the intersession reliability of pRF parameter estimates for the central visual field and near periphery, using a combined wedge and ring stimulus containing natural images. Sixteen healthy human participants completed two scanning sessions separated by 10–114 days. Individual participants showed very similar visual field maps for V1-V4 on both sessions. Intersession reliability for eccentricity and polar angle estimates was close to ceiling for most visual field maps (r>.8 for V1-3). PRF size and cortical magnification (CMF) estimates showed strong but lower overall intersession reliability (r≈.4–.6). Group level results for pRF size and CMF were highly similar between sessions. Additional control experiments confirmed that reliability does not depend on the carrier stimulus used and that reliability for pRF size and CMF is high for sessions acquired on the same day (r>.6). Our results demonstrate that pRF mapping is highly reliable across sessions

Cortical idiosyncrasies predict the perception of object size

Perception is subjective. Even basic judgments, like those of visual object size, vary substantially between observers and also across the visual field within the same observer. The way in which the visual system determines the size of objects remains unclear, however. We hypothesize that object size is inferred from neuronal population activity in V1 and predict that idiosyncrasies in cortical functional architecture should therefore explain individual differences in size judgments. Here we show results from novel behavioural methods and functional magnetic resonance imaging (fMRI) demonstrating that biases in size perception are correlated with the spatial tuning of neuronal populations in healthy volunteers. To explain this relationship, we formulate a population read-out model that directly links the spatial distribution of V1 representations to our perceptual experience of visual size. Taken together, our results suggest that the individual perception of simple stimuli is warped by idiosyncrasies in visual cortical organization

Does congenital deafness affect the structural and functional architecture of primary visual cortex?

Deafness results in greater reliance on the remaining senses. It is unknown whether the cortical architecture of the intact senses is optimized to compensate for lost input. Here we performed widefield population receptive field (pRF) mapping of primary visual cortex (V1) with functional magnetic resonance imaging (fMRI) in hearing and congenitally deaf participants, all of whom had learnt sign language after the age of 10 years. We found larger pRFs encoding the peripheral visual field of deaf compared to hearing participants. This was likely driven by larger facilitatory center zones of the pRF profile concentrated in the near and far periphery in the deaf group. pRF density was comparable between groups, indicating pRFs overlapped more in the deaf group. This could suggest that a coarse coding strategy underlies enhanced peripheral visual skills in deaf people. Cortical thickness was also decreased in V1 in the deaf group. These findings suggest deafness causes structural and functional plasticity at the earliest stages of visual cortex

Terrestrial habitat requirements of nesting freshwater turtles

Because particular life history traits affect species vulnerability to development pressures, cross-species summaries of life history traits are useful for generating management guidelines. Conservation of aquatic turtles, many members of which are regionally or globally imperiled, requires knowing the extent of upland habitat used for nesting. Therefore, we compiled distances that nests and gravid females had been observed from wetlands. Based on records of \u3e 8000 nests and gravid female records compiled for 31 species in the United States and Canada, the distances that encompass 95% of nests vary dramatically among genera and populations, from just 8 m for Malaclemys to nearly 1400 m for Trachemys. Widths of core areas to encompass varying fractions of nesting populations (based on mean maxima across all genera) were estimated as: 50% coverage = 93 m, 75% = 154 m, 90% = 198 m, 95% = 232 m, 100% = 942 m. Approximately 6–98 m is required to encompass each consecutive 10% segment of a nesting population up to 90% coverage; thereafter, ca. 424 m is required to encompass the remaining 10%. Many genera require modest terrestrial areas (\u3c200 m zones) for 95% nest coverage (Actinemys, Apalone, Chelydra, Chrysemys, Clemmys, Glyptemys, Graptemys, Macrochelys, Malaclemys, Pseudemys, Sternotherus), whereas other genera require larger zones (Deirochelys, Emydoidea, Kinosternon, Trachemys). Our results represent planning targets for conserving sufficient areas of uplands around wetlands to ensure protection of turtle nesting sites, migrating adult female turtles, and dispersing turtle hatchlings

Reducing weed biomass by burning and grazing can adversely affect frogs

The impacts of weed management on native biodiversity are often overlooked. Burning and grazing plots of land in isolation and in combination, were used to experimentally reduce the biomass of introduced para grass (Urochloa mutica(Forssk.) T.Q.Nguyen)) in a North Queensland wetland. Frogs were monitored to assess the impact of these management trials. Marbled frogs (Limnodynastes convexius-culus Macleay) declined in response to all management treatments, and their abundance was correlated with vegetation biomass. The abundance of spotted marsh frogs (Limnodynastes tasmaniensis Günther) was not related to weed control treatments, but was influenced by the distance of the experimental plot from the nearest woodland. The decline of these frog species in response to management trials indicates that knowledge about impacts of planned weed control is critical, to inform management of taxa that may be affected

Population receptive field tuning properties of visual cortex during childhood

Visuospatial abilities such as contrast sensitivity and Vernier acuity improve until late in childhood, but the neural mechanisms supporting these changes are poorly understood. We tested to which extent this development might reflect improved spatial sensitivity of neuronal populations in visual cortex. To do this, we measured BOLD-responses in areas V1-V4 and V3a, whilst 6- to 12-year-old children and adults watched large-field wedge and ring stimuli in the MRI scanner, and then fitted population receptive field (pRF) tuning functions to these data (Dumoulin and Wandell, 2008). Cortical magnification and pRF tuning width changed with eccentricity at all ages, as expected. However, there were no significant age differences in pRF size, shape, cortical magnification, or map consistency in any visual region. These findings thus strongly suggest that spatial vision in late childhood is not substantially limited by the spatial tuning of neuronal populations in early visual cortex. Instead, improvements in performance may reflect more efficient read-out of spatial information in early visual regions by higher-level processing stages, or prolonged tuning to more complex visual properties such as orientation. Importantly, this in-depth characterisation of the pRF tuning profiles across childhood, paves the way for in-vivo-testing of atypical visual cortex development and plasticity

Palliative pelvic exenteration: A systematic review of patient-centered outcomes

Objective: Palliative pelvic exenteration (PPE) is a technically complex operation with high morbidity and mortality rates, considered in patients with limited life expectancy. There is little evidence to guide practice. We performed a systematic review to evaluate the impact of PPE on symptom relief and quality of life (QoL). Methods: A systematic review was conducted according to the PRISMA guidelines using Ovid MEDLINE, EMBASe, and PubMed databases for studies reporting on outcomes of PPE for symptom relief or QoL. Descriptive statistics were used on pooled patient cohorts. Results: Twenty-three historical cohorts and case series were included, comprising 509 patients. No comparative studies were found. Most malignancies were of colorectal, gynaecological and urological origin. Common indications for PPE were pain, symptomatic fistula, bleeding, malodour, obstruction and pelvic sepsis. The pooled median postoperative morbidity rate was 53.6% (13\u2013100%), the median in-hospital mortality was 6.3% (0\u201366.7%), and median OS was 14 months (4\u201340 months). Some symptom relief was reported in a median of 79% (50\u2013100%) of the patients, although the magnitude of effect was poorly measured. Data for QoL measures were inconclusive. Five studies discouraged performing PPE in any patient, while 18 studies concluded that the procedure can be considered in highly selected patients. Conclusion: Available evidence on PPE is of low-quality. Morbidity and mortality rates are high with a short median OS interval. While some symptom relief may be afforded by this procedure, evidence for improvement in QoL is limited. A highly selective individualised approach is required to optimise the risk:benefit equation