Small Orientation Differences Research Articles

Gait-modifying effects of augmented-reality cueing in people with Parkinson's disease.

External cueing can improve gait in people with Parkinson's disease (PD), but there is a need for wearable, personalized and flexible cueing techniques that can exploit the power of action-relevant visual cues. Augmented Reality (AR) involving headsets or glasses represents a promising technology in those regards. This study examines the gait-modifying effects of real-world and AR cueing in people with PD. 21 people with PD performed walking tasks augmented with either real-world or AR cues, imposing changes in gait speed, step length, crossing step length, and step height. Two different AR headsets, differing in AR field of view (AR-FOV) size, were used to evaluate potential AR-FOV-size effects on the gait-modifying effects of AR cues as well as on the head orientation required for interacting with them. Participants modified their gait speed, step length, and crossing step length significantly to changes in both real-world and AR cues, with step lengths also being statistically equivalent to those imposed. Due to technical issues, step-height modulation could not be analyzed. AR-FOV size had no significant effect on gait modifications, although small differences in head orientation were observed when interacting with nearby objects between AR headsets. People with PD can modify their gait to AR cues as effectively as to real-world cues with state-of-the-art AR headsets, for which AR-FOV size is no longer a limiting factor. Future studies are warranted to explore the merit of a library of cue modalities and individually-tailored AR cueing for facilitating gait in real-world environments.

Remote imprinting of moiré lattices.

Two-dimensional moiré materials are formed by overlaying two layered crystals with small differences in orientation or/and lattice constant, where their direct coupling generates moiré potentials. Moiré materials have emerged as a platform for the discovery of new physics and device concepts, but while moiré materials are highly tunable, once formed, moiré lattices cannot be easily altered. Here we demonstrate the electrostatic imprinting of moiré lattices onto a target monolayer semiconductor. The moiré potential-created by a lattice of electrons that is supported by a Mott insulator state in a remote MoSe2/WS2 moiré bilayer-imprints a moiré potential that generates flat bands and correlated insulating states in the target monolayer and can be turned on/off by gate tuning the doping density of the moiré bilayer. Additionally, we studied the interplay between the electrostatic and structural relaxation contributions to moiré imprinting. Our results demonstrate a pathway towards gate control of moiré lattices.

Improving the Accuracy of Two-Color Multiview (2CMV) Advanced Geospatial Information (AGI) Products Using Unsupervised Feature Learning and Optical Flow.

In two-color multiview (2CMV) advanced geospatial information (AGI) products, temporal changes in synthetic aperture radar (SAR) images acquired at different times are detected, colorized, and overlaid on an initial image such that new features are represented in cyan, and features that have disappeared are represented in red. Accurate detection of temporal changes in 2CMV AGI products can be challenging because of ’speckle noise’ susceptibility and false positives that result from small orientation differences between objects imaged at different times. Accordingly, 2CMV products are often dominated by colored pixels when changes are detected via simple pixel-wise cross-correlation. The state-of-the-art in SAR image processing demonstrates that generating efficient 2CMV products, while accounting for the aforementioned problem cases, has not been well addressed. We propose a methodology to address the aforementioned two problem cases. Before detecting temporal changes, speckle and smoothing filters mitigate the effects of speckle noise. To detect temporal changes, we propose using unsupervised feature learning algorithms in conjunction with optical flow algorithms that track the motion of objects across time in small regions of interest. The proposed framework for distinguishing between actual motion and misregistration can lead to more accurate and meaningful change detection and improve object extraction from an SAR AGI product.

Reading Errors in Sundials with Incorrect Hour Lines: The Seventeenth-Century Sundial in Lerma

The restoration project of a seventeenth century sundial at Lerma (Spain) with incorrect engraved marks for the hour lines and devoid of its gnomon raised the issue of whether it is possible to predict what might be the reading errors when providing a new gnomon for it. Moreover, the analysis of possible slight changes in gnomon’s orientation and/or geometrical features to get better precisions was an appealing challenge. We must consider that Lerma’s case is not unique: templates were used in the past to engrave marks in numerous dials, and small differences in orientation were not taken into account. Differences in latitude under 0.5° were also neglected, by rounding off to integer values. Although Lerma’s sundial has been our guiding thread and its results are presented in detail, the method can be extrapolated to calculate reading errors for any dials with wrong marks for orientation or latitude different form the actual ones.

StimTrack: An open-source software for manual transcranial magnetic stimulation coil positioning

BackgroundDuring Transcranial Magnetic Stimulation (TMS) experiments researchers often use a neuronavigation system to precisely and accurately maintain coil position and orientation. New methodThis study aimed to develop and validate an open-source software for TMS coil navigation. StimTrack uses an optical tracker and an intuitive user interface to facilitate the maintenance of position and orientation of any type of coil within and between sessions. Additionally, online access to navigation data is provided, hereby adding e.g. the ability to start or stop the magnetic stimulator depending on the distance to target or the variation of the orientation angles. ResultsStimTrack allows repeatable repositioning of the coil within 0.7mm for translation and <1° for rotation. Stimulus-response (SR) curves obtained from 19 healthy volunteers were used to demonstrate that StimTrack can be effectively used in a typical experiment. An excellent intra and inter-session reliability (ICC >0.9) was obtained on all parameters computed on SR curves acquired using StimTrack. Comparison with existing methodStimTrack showed a target accuracy similar to that of a commercial neuronavigation system (BrainSight, Rogue Research Inc.). Indeed, small differences both in position (∼0.2mm) and orientation (<1°) were found between the systems. These differences are negligible given the human error involved in landmarks registration. ConclusionsStimTrack, available as supplementary material, is found to be a good alternative for commercial neuronavigation systems facilitating assessment changes in corticospinal excitability using TMS. StimTrack allows researchers to tailor its functionality to their specific needs, providing added value that benefits experimental procedures and improves data quality.

Binocular contrast, stereopsis, and rivalry: Toward a dynamical synthesis

It is well known that small orientation differences between two monocular gratings fuse to generate a stereoscopic perception of tilt, while large differences trigger binocular rivalry. In addition, unequal monocular contrasts combine nonlinearly to generate binocular contrast. A nonlinear neural model is developed here to account for binocular contrast, fusion at small orientation differences, and rivalry at large differences. The model also accounts for hysteresis in the transition between fusion and rivalry. Finally, the model predicts that interocular contrast differences between fusible gratings will produce a reduced tilt percept, and experiments reported here support this. Key to the model is the presence of two classes of inhibitory interneurons: one operating on similar orientations to normalize interocular contrast (IN), and one operating across large orientation differences to generate rivalry (IR). Critically, the IN neurons switch off the IR neurons driven by the other eye, thus permitting fusion of binocular plaids.

Different Orientation Tuning of Near- and Far-Surround Suppression in Macaque Primary Visual Cortex Mirrors Their Tuning in Human Perception

In primary visual cortex (V1), neuronal responses to stimuli inside the receptive field (RF) are usually suppressed by stimuli in the RF surround. This suppression is orientation specific. Similarly, in human vision surround stimuli can suppress perceived contrast of a central stimulus in an orientation-dependent manner. The surround consists of two regions likely generated by different circuits: a near-surround generated predominantly by geniculocortical and intra-V1 horizontal connections, and a far-surround generated exclusively by interareal feedback. Using stimuli confined to the near- or far-surround of V1 neurons, and similar stimuli in human psychophysics, we find that near-surround suppression is more sharply orientation tuned than far-surround suppression in both macaque V1 and human perception. These results point to a similarity between surround suppression in macaque V1 and human vision, and suggest that feedback circuits are less orientation biased than horizontal circuits. We find the sharpest tuning of near-surround suppression in V1 layers (3, 4B, 4Cα) with patterned and orientation-specific horizontal connections. Sharpest tuning of far-surround suppression occurs in layer 4B, suggesting greater orientation specificity of feedback to this layer. Different orientation tuning of near- and far-surround suppression may reflect a statistical bias in natural images, whereby nearby edges have higher probability than distant edges of being co-oriented and belonging to the same contour. Surround suppression would, thus, increase the coding efficiency of frequently co-occurring contours and the saliency of less frequent ones. Such saliency increase can help detect small orientation differences in nearby edges (for contour completion), but large orientation differences in distant edges (for directing saccades/attention).

An analysis of subdomain orientation, conformational change and disorder in relation to crystal packing of aspartic proteinases

The analysis reported here describes detailed structural studies of endothiapepsin (the aspartic proteinase from Endothia parasitica), with and without bound inhibitors, and human pepsin 3b. Comparison of multiple crystal structures of members of the aspartic proteinase family has revealed small but significant differences in domain orientation in different crystal forms. In this paper, it is shown that these differences in domain orientation do not necessarily correlate with the presence or absence of bound inhibitors, but appear to stem at least partly from crystal contacts mediated by sulfate ions. However, since the same inherent flexibility of the structure is observed for other enzymes in this family such as human pepsin, the native structure of which is also reported here, the observed domain movements may well have implications for the mechanism of catalysis.

Practicing Coarse Orientation Discrimination Improves Orientation Signals in Macaque Cortical Area V4

Practice improves the performance in visual tasks, but mechanisms underlying this adult brain plasticity are unclear. Single-cell studies reported no [1], weak [2], or moderate [3, 4] perceptual learning-related changes in macaque visual areas V1 and V4, whereas none were found in middle temporal (MT) [5]. These conflicting results and modeling of human (e.g., [6, 7]) and monkey data [8] suggested that changes in the readout of visual cortical signals underlie perceptual learning, rather than changes in these signals. In the V4 learning studies, monkeys discriminated small differences in orientation, whereas in the MT study, the animals discriminated opponent motion directions. Analogous to the latter study, we trained monkeys to discriminate static orthogonal orientations masked by noise. V4 neurons showed robust increases in their capacity to discriminate the trained orientations during the course of the training. This effect was observed during discrimination and passive fixation but specifically for the trained orientations. The improvement in neural discrimination was due to decreased response variability and an increase of the difference between the mean responses for the two trained orientations. These findings demonstrate that perceptual learning in a coarse discrimination task indeed can change the response properties of a cortical sensory area.

The role of co-circularity of local elements in texture perception

The present study analyzes the effect of local pairwise orientation relations on the perception of textural structure. We have employed a new class of stochastic stimuli comprised of paired Gabor patches with a particular orientation difference (theta) and relative angular position (phi). We measured the threshold proportion of signal pairs for discriminating the target texture from a noise texture comprised of randomly oriented pairs. The results showed that observers were sensitive not only to textures containing pairs with curvilinear configurations such as lines and curves (phi = theta / 2), but also to their orthogonal configurations such as V shapes and parallels (phi = theta / 2 + 90). Both classes of configuration exhibit the property of co-circularity, a fundamental geometric feature of edges and contours in natural images. We also found higher sensitivity for textures made from orientation pairs with either large or small orientation differences. These results suggest that in addition to orientation difference, co-circularity plays a critical role in the perception of orientation-based textural structure.

A comparison of fMRI adaptation and multivariate pattern classification analysis in visual cortex

Functional magnetic resonance imaging (fMRI) has become a ubiquitous tool in cognitive neuroscience. The technique allows noninvasive measurements of cortical responses in the human brain, but only on the millimeter scale. Because a typical voxel contains many thousands of neurons with varied properties, establishing the selectivity of their responses directly is impossible. In recent years, two methods using fMRI aimed at studying the selectivity of neuronal populations on a ‘subvoxel’ scale have been heavily used. The first technique, fMRI adaptation, relies on the observation that the blood oxygen level-dependent (BOLD) response in a given voxel is reduced after prolonged presentation of a stimulus, and that this reduction is selective to the characteristics of the repeated stimuli (adapters). The second technique, multivariate pattern analysis (MVPA), makes use of multivariate statistics to recover small biases in individual voxels in their responses to different stimuli. It is thought that these biases arise due to the uneven distribution of neurons (with different properties) sampled by the many voxels in the imaged volume. These two techniques have not been compared explicitly, however, and little is known about their relative sensitivities. Here, we compared fMRI results from orientation-specific visual adaptation and orientation–classification by MVPA, using optimized experimental designs for each, and found that the multivariate pattern classification approach was more sensitive to small differences in stimulus orientation than the adaptation paradigm. Estimates of orientation selectivity obtained with the two methods were, however, very highly correlated across visual areas.

Cross-orientation interactions in human vision

Humans can discriminate one visual contour from another on the basis of small differences in orientation. This capability depends on cortical detectors that are selective for a small range of orientations. We have measured this orientation bandwidth and the suppression that helps to shape it, with a reverse correlation technique. Human subjects were presented with a stream of randomly oriented gratings at a rate of 30 per second. Their task was to press a key whenever they saw an orientation nominated as the target. We analyzed the data by finding the probability density of two orientations: One preceded the key-press by the reaction time, and the second preceded the first by up to 100 ms. The results were as follows: (1) One grating facilitated the following one in producing a key-press when the gratings differed little in orientation. The estimate of orientation bandwidth resulting from this facilitation was 38 degrees . (2) A large angle between the two orientations reduced the probability of a key-press. This finding was best modelled as a suppression that did not vary with orientation, consistent with the idea that cross-orientation suppression is non-oriented. (3) Analysis of non-consecutive grating pairs showed that cross-orientation interactions lasted no longer than 67 ms.

The influence of proton irradiation on the microstructure of pure Al films

In this work, we investigated the microstructures of pure aluminum films irradiated with 160 keV proton by varying the irradiation dose. The vacancy clusters induced by proton irradiation in Al films are characterized by TEM, and the density and size distribution are determined. In the irradiation dose range of our studies, the density and size of vacancy clusters and the dislocation density increase with increasing irradiation dose. Our experimental results show that the dislocation density and size of vacancy clusters increase as the irradiation dose increases from 1×1011 to 4×1011/mm2. When the irradiation dose is as high as 6×1011/mm2, the number density of dislocation loops decreases, while the size of dislocation loop increases obviously. The vacancies tend to form larger clusters, accompanied by the formation of banded structures in the irradiated sample at higher irradiation doses. We found that there were small crystal orientation differences among the boundaries of banded structure. This banded structure is closely related to the degradation of mechanical and physical performance of irradiated material.

Bone microstructure: quantifying bone vascular orientation

Bone microstructure often preserves a temporal record of the life history of the animal to which it belongs. Previously used bone microstructure metrics to differentiate between primary bone types are reviewed and tested with a broad sample of bone types. Two new metrics, the radial index and the longitudinal index, are developed to quantitatively differentiate bone types based on bone vascular orientation in three dimensions. All previously used metrics described the bone microstructure in a nonlinear pattern and were unable to separate bone types satisfactorily. The radial index and longitudinal index effectively differentiated bone types and described bone microstructure within a linear continuum. The continuous nature of the range of vascular orientation in bone microstructure necessitates a quantitative approach rather than the commonly used qualitative classifications. The radial index and longitudinal index, which objectively detect small differences in vascular orientation in three dimensions, are therefore preferable to other metrics for inter- and intra-specific comparisons of bone microstructure. These metrics offer novel methods to facilitate examinations of the relationship between primary bone type and ontogeny, biomechanics, and phylogeny.

The processing of linear perspective and binocular information for action and perception

To investigate the processing of linear perspective and binocular information for action and for the perceptual judgment of depth, we presented viewers with an actual Ames trapezoidal window. The display, when presented perpendicular to the line of sight, provided perspective information for a rectangular window slanted in depth, while binocular information specified a planar surface in the fronto-parallel plane. We compared pointing towards the display-edges with perceptual judgment of their positions in depth as the display orientation was varied under monocular and binocular view. On monocular trials, pointing and depth judgment were based on the perspective information and failed to respond accurately to changes in display orientation because pictorial information did not vary sufficiently to specify the small differences in orientation. For binocular trials, pointing was based on binocular information and precisely matched the changes in display orientation whereas depth judgment was short of such adjustment and based upon both binocular and perspective-specified slant information. The finding, that on binocular trials pointing was considerably less responsive to the illusion than perceptual judgment, supports an account of two separate processing streams in the human visual system, a ventral pathway involved in object recognition and a dorsal pathway that produces visual information for the control of actions. Previously, similar differences between perception and action were explained by an alternate explanation, that is, viewers selectively attend to different parts of a display in the two tasks. The finding that under monocular view participants responded to perspective information in both the action and the perception task rules out the attention-based argument.

Learning to See the Difference Specifically Alters the Most Informative V4 Neurons

Perceptual learning is an instance of adult plasticity whereby training in a sensory (e.g., a visual task) results in neuronal changes leading to an improved ability to perform the task. Yet studies in primary visual cortex have found that changes in neuronal response properties were relatively modest. The present study examines the effects of training in an orientation discrimination task on the response properties of V4 neurons in awake rhesus monkeys. Results indicate that the changes induced in V4 are indeed larger than those in V1. Nonspecific effects of training included a decrease in response variance, and an increase in overall orientation selectivity in V4. The orientation-specific changes involved a local steepening in the orientation tuning curve around the trained orientation that selectively improved orientation discriminability at the trained orientation. Moreover, these changes were largely confined to the population of neurons whose orientation tuning was optimal for signaling small differences in orientation at the trained orientation. Finally, the modifications were restricted to the part of the tuning curve close to the trained orientation. Thus, we conclude that it is the most informative V4 neurons, those most directly involved in the discrimination, that are specifically modified by perceptual learning.

Behavioural discrimination of polarized light in the damselfishChromis viridis(family Pomacentridae)

In this study, we demonstrate the capacity for damselfish (green chromis, Chromis viridis) to discriminate between different e-vector orientations of ultraviolet polarized light. We examined the ability of green chromis to resolve small differences in e-vector orientation of ultraviolet polarized light. Fish were successfully trained to swim towards an e-vector orientation of polarized light using a behavioural chamber. C. viridis was able to discriminate between the horizontal and the vertical plane of ultraviolet polarized light independent of brightness content of the stimuli. However, e-vector discrimination capability disappeared when the ultraviolet portion of the light stimuli was removed, indicating that the presence of ultraviolet light was critical for e-vector discrimination. Fish could also distinguish between relatively small e-vector orientations of ultraviolet polarized light. Functional implications for high e-vector discriminative capabilities could be used in functional domains such as feeding and communication.

Cooperative and temporally structured information in the visual cortex

We have examined the information contained in the coordination of groups of cells in the primary visual cortex of the cat recorded with a 5×5 microelectrode array. When testing small differences (<10°) in stimulus orientation with an information-theoretic distance, response discrimination depended on the temporal resolution of response sampling and improved when including response history. Joint activity also enhanced response discrimination and the enhancement was proportionally larger when more cells were sampled. Spike timing and intervals provided information about fine orientation differences. Even a small rotation of the visual stimulus produced clear time shifts in the response structure with little or no change in the spike count. Larger orientation differences (>10°) are discriminated easily on the basis of the independent spike counts. We conclude that synchrony provides a reliable mechanism to transmit fine structure of visual information and offers an efficient cooperative neural code that we have only begun to explore.

Generating Misorientations in Shear Deformation Structures

Of considerable importance to the generation of ultrafine microstructures is the development of high misorientations. The present work examines the effect of the crystallographic rotation field in simple shear upon the evolution of misorientation during plastic working. A series of Taylor simulations are presented and it is shown that the rotation field is such that small differences in orientation in the region of the main torsion texture components are considerably increased with the application of shear strain. This did not occur in simulations of rolling. The torsion simulations compare favourably with the nature of the misorientations evident in hot worked 1050 Al and Ti-IF steel. It is concluded that shear deformation, by its nature, facilitates the generation of higher misorientations.

Cooperation between Area 17 Neuron Pairs Enhances Fine Discrimination of Orientation

We examined 66 complex cells in area 17 of cats that were paralyzed and anesthetized with propofol and N2O. We studied changes in ensemble responses for small (<10 degrees ) and large (>10 degrees ) differences in orientation. Examination of temporal resolution and discharge history revealed advantages in discrimination from both dependent (e.g., synchronization) and independent (e.g., bursting) interspike interval properties. For 27 pairs of neurons, we found that the average cooperation (the advantage gained from the joint activity) was 57.6% for fine discrimination of orientation but <5% for gross discrimination. Dependency (probabilistic quantification of the interaction between the cells) was measured between 29 pairs of neurons while varying orientation. On average, the dependency tuning for orientation was 35.5% narrower than the average firing rate tuning. The changes in dependency around the peak orientation (at which the firing rate remains relatively constant) lead to substantial cooperation that can improve discrimination in this region. The narrow tuning of dependency and the cooperation provide evidence to support a population-encoding scheme that is based on biologically plausible mechanisms and that could account for hyperacuities.