Evidence for Auto-Correlation and Symmetry Detection in Primary Visual Cortex

The detectability of patterns in random dot arrays was measured as a function of dot density and compared with the statistical limit set by different methods of detecting the pattern. For filtering, cross-correlation, convolution, or template matching, the limit is expected to be inversely proportional to the square root of dot density. But for auto-correlation, which can detect symmetries of various types, the limit is unaffected by dot density under many conditions. Confirming previous results, we found that the coherence-threshold is often constant for Glass patterns, but the range of constancy depends on details of the display procedure. Coherence-thresholds were found to increase when the average number of dots expected at each location rose towards or exceeded a value of one; we therefore think it results from the non-linear effects of occlusion that occur when a later-programmed dot falls in the same location as an earlier one. To test this, these non-linear effects were prevented by arranging the luminance of each location to be directly proportional to the number of times that location was covered by a dot. Millions of dots can be used for these images, and they retain the streakiness of Glass patterns, while discrete dots disappear. The constant coherence threshold for detecting this streakiness is maintained over a huge range of dot densities, extending right down to the range where discrete dots become visible and up to patterns that are essentially full-tone images with no discrete dots. At threshold, all these patterns have similar auto-correlation functions, as we can see from the way both low dot-number Glass-patterns and these mega-dot, multi-tone, Glass-like images are formed. This startling fact raises the question whether primary visual cortex computes auto-correlations as well as, or even instead of, the local, Fourier-type, wavelet analysis of the currently popular paradigm

Evidence for a neural model to evaluate symmetry in V1

50 years ago Hubel and Wiesel discovered simple and complex cells in V1, but there is still no consensus on their functional roles. It is agreed that complex cells are more often selective for direction of motion than simple cells, that there are differences in the way they combine information within their receptive fields, and that complex cells probably receive most of their input from simple cells, but what this serial hierarchy achieves is not understood. There is another puzzling dichotomy that we think is related, namely that of cross-correlation, which is widely accepted as the operation performed on the input image by simple cells, and auto-correlation, which some think underlies the perception of Glass patterns, and possibly motion. We propose the hypothesis that complex cells signal auto-correlations in the visual image, but to evaluate them they require the preliminary analysis done by simple cells, and also pinwheels - structures intervening between simple cells and complex cells that were quite unknown to Hubel and Wiesel. We shall first present psychophysical evidence, using a new kind of random dot display, which suggests that both cross-correlation and auto-correlation are performed in early vision. We then point to recent evidence on the micro-circuitry of pinwheels, and mappings of their intrinsic activity, which shows how pinwheels might enable complex cells to respond selectively to autocorrelations in the input image that activates the simple cells. Auto-correlation is a powerful tool for detecting symmetry, and many may be surprised by evidence that such an abstract property is detected so early in visual perception

Assessing the performance of protective winter covers for outdoor marble statuary: pilot investigation

Outdoor statuary in gardens and parks in temperate climates has a tradition of being covered during the winter, to protect against external conditions. There has been little scientific study of the environmental protection that different types of covers provide. This paper examines environmental conditions provided by a range of covers used to protect marble statuary at three sites in the UK. The protection required depends upon the condition of the marble. Although statues closely wrapped and with a layer of insulation provide good protection, this needs to be considered against the potential physical damage of close wrapping a fragile deteriorated surface

A model for incorporating a clinically-feasible exercise test in paraplegic annual reviews : a tool for stratified cardiopulmonary stress performance classification and monitoring

To identify and characterize an exercise test for use in routine spinal cord injury clinical review, and (ii) to describe levels of, and factors affecting, cardiopulmonary stress performance during exercise in the chronic paraplegic population in Scotland, UK. Cross-sectional study Queen Elizabeth National Spinal Injuries Unit (Glasgow, Scotland) 48 subjects with chronic paraplegia resulting from spinal cord injury at neurological levels T2-L2 Peak oxygen uptake, peak power output, gas exchange threshold and peak heart rate were determined from an incremental arm-cranking exercise test. Using a general linear model, the effects of gender, high (injury level above T6) versus low paraplegia, time since injury, body mass and age on peak oxygen uptake and peak power output were investigated. All 48 subjects completed the arm-cranking exercise test, which was shown to be practical for fitness screening in paraplegia. Men (n=38) had a peak oxygen uptake of 1.302 +/- 0.326 l.min-1 (mean +/- s.d.) and peak power output of 81.6 +/- 23.2W, which was significantly higher than for women (n=10), at 0.832 +/- 0.277 l.min-1 and 50.1 +/- 27.8 W, respectively. There was large intersubject variability in cardiopulmonary performance during arm-cranking exercise testing, but the overall mean for the Scottish population was lower than reference values from other countries. Arm-cranking exercise tests are feasible in the clinical environment. The motivation for their implementation is threefold: (i) to determine cardiopulmonary stress performance of individual paraplegic patients, (ii) to stratify patients into cardiovascular risk categories, and (iii) to monitor the effects of targeted exercise prescription

Abdominal functional electrical stimulation to assist ventilator weaning in acute tetraplegia: a cohort study

Background Severe impairment of the major respiratory muscles resulting from tetraplegia reduces respiratory function, causing many people with tetraplegia to require mechanical ventilation during the acute stage of injury. Abdominal Functional Electrical Stimulation (AFES) can improve respiratory function in non-ventilated patients with sub-acute and chronic tetraplegia. The aim of this study was to investigate the clinical feasibility of using an AFES training program to improve respiratory function and assist ventilator weaning in acute tetraplegia.<p></p> Methods AFES was applied for between 20 and 40 minutes per day, five times per week on four alternate weeks, with 10 acute ventilator dependent tetraplegic participants. Each participant was matched retrospectively with a ventilator dependent tetraplegic control, based on injury level, age and sex. Tidal Volume (VT) and Vital Capacity (VC) were measured weekly, with weaning progress compared to the controls.<p></p> Results Compliance to training sessions was 96.7%. Stimulated VT was significantly greater than unstimulated VT. VT and VC increased throughout the study, with mean VC increasing significantly (VT: 6.2 mL/kg to 7.8 mL/kg VC: 12.6 mL/kg to 18.7 mL/kg). Intervention participants weaned from mechanical ventilation on average 11 (sd: ± 23) days faster than their matched controls.<p></p> Conclusion The results of this study indicate that AFES is a clinically feasible technique for acute ventilator dependent tetraplegic patients and that this intervention may improve respiratory function and enable faster weaning from mechanical ventilation.<p></p&gt

Testing general relativity using golden black-hole binaries

The coalescences of stellar-mass black-hole binaries through their inspiral, merger, and ringdown are among the most promising sources for ground-based gravitational-wave (GW) detectors. If a GW signal is observed with sufficient signal-to-noise ratio, the masses and spins of the black holes can be estimated from just the inspiral part of the signal. Using these estimates of the initial parameters of the binary, the mass and spin of the final black hole can be uniquely predicted making use of general-relativistic numerical simulations. In addition, the mass and spin of the final black hole can be independently estimated from the merger--ringdown part of the signal. If the binary black hole dynamics is correctly described by general relativity (GR), these independent estimates have to be consistent with each other. We present a Bayesian implementation of such a test of general relativity, which allows us to combine the constraints from multiple observations. Using kludge modified GR waveforms, we demonstrate that this test can detect sufficiently large deviations from GR, and outline the expected constraints from upcoming GW observations using the second-generation of ground-based GW detectors.Comment: 5 pages, 2 fig

Response Validity in Forensic Neuropsychology: Exploratory Factor Analytic Evidence of Distinct Cognitive and Psychological Constructs

Forensic neuropsychology studies usually address either cognitive effort or psychological response validity. Whether these are distinct constructs is unclear. In 122 participants evaluated in a compensation-seeking context, the present Exploratory Factor Analysis examined whether forced-choice cognitive effort measures (Victoria Symptom Validity Test, Test of Memory Malingering, Letter Memory Test) and Minnesota Multiphasic Personality Inventory, Second Edition (MMPI-2) validity scales (L, F, K, FBS, Fp, RBS, Md, Dsr2, S) load on independent factors. Regardless of factor rotation strategy (orthogonal or oblique), four response validity factors emerged by means of both Principal Components Analysis (82.7% total variance) and Principal-Axis Factor Analysis (74.1% total variance). The four factors were designated as follows: Factor I, with large loadings from L, K, and S—underreporting of psychologicalsymptoms; Factor II, with large loadings from FBS, RBS, and Md—overreporting of neurotic symptoms; Factor III, with large loadings from VSVT, TOMM, and LMT—insufficient cognitive effort; and Factor IV, with the largest loadings from F, Fp, and Dsr2—overreporting of psychotic/rarely endorsed symptoms. Results reflect the heterogeneity of response validity in forensic samples referred for neuropsychological evaluation. Administration of both cognitive effort measures and psychological validity scales is imperative to accurate forensic neuropsychological assessment. (JINS, 2007, 13, 440–449.

Spatial Variations in Nutrient and Microbial Transport from Feedlot Surfaces

Nutrient and microbial transport by runoff may vary at different locations within a beef cattle feedlot. If the areas making the largest contributions to nutrient and microbial transport can be identified, it may be possible to institute site‐specific management practices to reduce runoff nutrient and microbial transport. The objectives of this study were to: (1) measure selected feedlot soil properties and nutrient and microbial transport in runoff from various feedlot locations, (2) compare the effects of unconsolidated surface materials (USM) (loose manure pack) and consolidated subsurface materials (CSM) (compacted manure and underlying layers) on nutrient and microbial transport, and (3) determine if nutrient and microbial transport in runoff are correlated to selected feedlot soil characteristics. Simulated rainfall events were applied to 0.75 m wide by 2 m long plots. No significant differences (P \u3c 0.05) in feedlot soil characteristics or nutrient transport in runoff were found between USM and CSM. However, concentrations of E. coli were significantly greater in the USM than the CSM. Pen location was found to significantly influence feedlot soil measurements of Bray‐1 P, calcium, chloride, copper, electrical conductivity (EC), loss on ignition, organic N, phosphorus, potassium, sodium, sulfur, total N (TN), water‐soluble P, and zinc. Runoff measurements of dissolved phosphorus (DP), EC, and NH4-N were significantly influenced by pen location and were correlated to selected feedlot soil characteristics. Thus, it may be possible to estimate DP, EC, and NH4-N in runoff from selected feedlot soil parameters