A GENERIC GLARE SENSATION MODEL BASED ON THE HUMAN VISUAL SYSTEM

Conventional discomfort glare measures are based on glare source properties like luminous intensity or luminance and typically are valid only to specific situations and to specific types of light sources. For instance, the Unified Glare Rating (UGR) is intended for indoor lighting conditions with medium-sized glare sources, whereas another class of discomfort glare measures is specifically devoted to car headlamps. Recently, CIE TC 3-57 started with the aim to develop a more generic glare sensation model based on the human visual system. We present an example of such a model, including a detailed description of aspects like pupil constriction, retinal image formation, photoreceptor response and adaptation, receptive field-type filtering in the retina, and neural spatial summation. The linear correlation of the model to UGR in an indoor setting, and to subjective glare responses in an outdoor-like setting indicate that the human-visual-system-based model may indeed be considered generic.

Synthesis of a comprehensive population code for contextual features in the awake sensory cortex

How cortical circuits build representations of complex objects is poorly understood. Individual neurons must integrate broadly over space, yet simultaneously obtain sharp tuning to specific global stimulus features. Groups of neurons identifying different global features must then assemble into a population that forms a comprehensive code for these global stimulus properties. Although the logic for how single neurons summate over their spatial inputs has been well-explored in anesthetized animals, how large groups of neurons compose a flexible population code of higher order features in awake animals is not known. To address this question, we probed the integration and population coding of higher order stimuli in the somatosensory and visual cortices of awake mice using two-photon calcium imaging across cortical layers. We developed a novel tactile stimulator that allowed the precise measurement of spatial summation even in actively whisking mice. Using this system, we found a sparse but comprehensive population code for higher order tactile features that depends on a heterogeneous and neuron-specific logic of spatial summation beyond the receptive field. Different somatosensory cortical neurons summed specific combinations of sensory inputs supra-linearly, but integrated other inputs sub-linearly, leading to selective responses to higher order features. Visual cortical populations employed a nearly identical scheme to generate a comprehensive population code for contextual stimuli. These results suggest that a heterogeneous logic of input-specific supra-linear summation may represent a widespread cortical mechanism for the synthesis of sparse higher order feature codes in neural populations. This may explain how the brain exploits the thalamocortical expansion of dimensionality to encode arbitrary complex features of sensory stimuli.

Optical Sensitivity of Camera-Like Eyes to White Light

Gastropod mollusks are convenient model organisms for studying the functioning of the visual system. The purpose of this work is to estimate the value of the optical sensitivity to white light for the camera-like eyes of gastropod mollusks and humans and analyze its effect on the spatial resolving power in two regions of the retina: in the center—for single photoreceptors of the first/second type in a mollusk and single cones in humans—and in the periphery—for single photoreceptors of the first/second type in a mollusk, as well as for single rods/cones and their groups, subject to spatial summation in humans. The methods of histology, light and transmission electron microscopy, morphometry, calculations and methods of statistical analysis are used in the work. In a mollusk, with a fixed pupil area, the value of the optical sensitivity of the eye to white light in the center of the retina for single photoreceptors of the first/second type is 0.5/0.006 μm2·sr and in the periphery of the retina, 0.9/0.009 μm2·sr. In humans, at the minimum and maximum pupil area, respectively, the value of the optical sensitivity of the eye to white light in the center of the retina (foveola) for single cones varies from 0.00053 to 0.028 μm2·sr, and in the periphery of the retina (far periphery) for single rods from 0.011 to 0.575 μm2·sr, for single cones from 0.025 to 1.319 μm2·sr, for the groups of rods from 3859 to 204,094 μm2·sr and for the groups of cones from 2.5 to 131 μm2·sr. The value of the optical sensitivity of the eyes to white light for single photoreceptors of the first/second type in both regions of the retina in a mollusk, as well as for single cones in the center and groups of rods/cones in the periphery of the retina in humans, corresponds to the ambient light conditions during periods of activity and does not affect the spatial resolving power.

Hierarchical Timescales in the Neocortex: Mathematical Mechanism and Biological Insights

A cardinal feature of the neocortex is the progressive increase of the spatial receptive fields along the cortical hierarchy. Recently, theoretical and experimental findings have shown that the temporal response windows also gradually enlarge, so that early sensory neural circuits operate on short-time scales whereas higher association areas are capable of integrating information over a long period of time. While an increased receptive field is accounted for by spatial summation of inputs from neurons in an upstream area, the emergence of timescale hierarchy cannot be readily explained, especially given the dense inter-areal cortical connectivity known in modern connectome. To uncover the required neurobiological properties, we carried out a rigorous analysis of an anatomically-based large-scale cortex model of macaque monkeys. Using a perturbation method, we show that the segregation of disparate timescales is defined in terms of the localization of eigenvectors of the connectivity matrix, which depends on three circuit properties: (1) a macroscopic gradient of synaptic excitation, (2) distinct electrophysiological properties between excitatory and inhibitory neuronal populations, and (3) a detailed balance between long-range excitatory inputs and local inhibitory inputs for each area-to-area pathway. Our work thus provides a quantitative understanding of the mechanism underlying the emergence of timescale hierarchy in large-scale primate cortical networks.

Vibration Perception Thresholds of Skin Mechanoreceptors Are Influenced by Different Contact Forces

Determining vibration perception thresholds (VPT) is a central concern of clinical research and science to assess the somatosensory capacity of humans. The response of different mechanoreceptors to an increasing contact force has rarely been studied. We hypothesize that increasing contact force leads to a decrease in VPTs of fast-adapting mechanoreceptors in the sole of the human foot. VPTs of 10 healthy subjects were measured at 30 Hz and 200 Hz at the heel of the right foot using a vibration exciter. Contact forces were adjusted precisely between 0.3 N–9.6 N through an integrated force sensor. Significant main effects were found for frequency and contact force. Furthermore, there was a significant interaction for frequency and contact force, meaning that the influence of an increasing contact force was more obvious for the 30 Hz condition. We presume that the principles of contrast enhancement and spatial summation are valid in Meissner and Pacinian corpuscles, respectively. In addition to spatial summation, we presume an effect on Pacinian corpuscles due to their presence in the periosteum or interosseous membrane.

Effect of tibial plateau levelling osteotomy and rehabilitation on muscle function in cruciate-deficient dogs evaluated with acoustic myography

The objective of the study was to determine the function of the biceps femoris, quadriceps, gastrocnemius and semitendinosus muscles at the walk in dogs with unilateral clinical cruciate disease and palpable joint instability. To compare function before and after a tibial plateau levelling osteotomy (TPLO) procedure, and after six weeks of subsequent rehabilitation therapy. Fourteen adult client-owned dogs with cranial cruciate ligament deficiency (CCLD). Orthopaedic examination, temporospatial gait analysis and acoustic myography (AMG) recordings were made at three time points: before TPLO, and post-operatively at two and eight weeks. A rehabilitation program started 2 weeks after surgery and was either in-clinic along with in-home rehabilitation or in-home only. Statistics included: repeated measures ANOVA and paired t-tests. Significance was set at P<0.05. When comparing the affected versus the unaffected limb in the CCLD dogs, there were no significant differences found in AMG values between baseline and other time points for the quadriceps and semitendinosus muscles. The gastrocnemius and biceps femoris muscles had a significant change in spatial summation (S) score over time. The gastrocnemius (S) score was not significantly different to the unaffected limb by 8 weeks post TPLO. There was no significant effect of rehabilitation method on S score. Dogs with in-clinic rehabilitation regained more symmetry in thigh circumference versus in-home only. Lameness parameters improved but did not completely resolve in all dogs by week 8 post TPLO. The function of the gastrocnemius muscles in affected limbs was significantly different to normal limbs at baseline and 2 weeks post TPLO but not at 8 weeks. Thigh symmetry, but no other parameters, was improved with the addition of in-clinic rehabilitation.

Investigation of Correlations Between Pain Modulation Paradigms

Objective Endogenous pain modulation can be quantified through the use of various paradigms. Commonly used paradigms include conditioned pain modulation (CPM), offset analgesia (OA), spatial summation of pain (SSP), and temporal summation of pain (TSP), which reflect spatial and temporal aspects of pro- and antinociceptive processing. Although these paradigms are regularly used and are of high clinical relevance, the underlying physiological mechanisms are not fully understood. Design The aim of this study is therefore to assess the association between these paradigms by using comparable protocols and methodological approaches. Setting University campus. Subjects Healthy and pain-free volunteers (n = 48) underwent psychophysical assessment of CPM, OA, SSP, and TSP (random order) at the same body area (volar nondominant forearm) with individualized noxious stimuli. Methods CPM included heat stimuli before, during, and after a noxious cold-water bath, whereas for OA, three heat stimuli were applied: baseline trial, offset trial, and constant trial. For the SSP paradigm, two differently sized heat stimulation areas were evaluated, whereas for TSP, the first and last stimulus of 10 consecutive short heat stimuli were assessed. A computerized visual analog scale was used to continuously evaluate pain intensity. The magnitudes of all associations between all paradigm pairs were analyzed with Spearman’s correlation, and individual influencing factors were assessed with a multivariate linear regression model. Results Weak to moderate correlations among all four paradigms were found (P &gt; 0.05), and no distinct influencing factors were identified. Conclusions A limited association between pain modulation paradigms suggests that CPM, OA, SSP, and TSP assess distinct aspects of endogenous analgesia with different underlying physiological mechanisms.

Near-surface diffractor detection at archaeological sites based on an interferometric workflow

Detecting small-size objects is a primary challenge at archaeological sites due to the high degree of heterogeneity present in the near surface. Although high-resolution reflection seismic imaging often delivers the target resolution of the subsurface in different near-surface settings, the standard processing for obtaining an image of the subsurface is not suitable to map local diffractors. This happens because shallow seismic-reflection data are often dominated by strong surface waves which might cover weaker diffractions, and because traditional common-midpoint moveout corrections are only optimal for reflection events. Here, we propose an approach for imaging subsurface objects using masked diffractions. These masked diffractions are firstly revealed by a combination of seismic interferometry and nonstationary adaptive subtraction, and then further enhanced through crosscoherence-based super-virtual interferometry. A diffraction image is then computed by a spatial summation of the revealed diffractions. We use phase-weighted stack to enhance the coherent summation of weak diffraction signals. Using synthetic data, we show that our scheme is robust in locating diffractors from data dominated by strong Love waves. We test our method on field data acquired at an archaeological site. The resulting distribution of shallow diffractors agrees with the location of anomalous objects identified in the Vs model obtained by elastic SH/Love full-waveform inversion using the same field data. The anomalous objects correspond to the position of a suspected burial, also detected in an independent magnetic survey and corings.