Apparent Motion Research Articles

Universal Solution of Medieval Spherical Astronomy

Spherical astronomy is a part of astronomy that figures of the sky as a sphere. It concerns the study of astronomical coordinate frames, the direction and apparent motion of celestial bodies, the determination of positions from astronomical observations, and the errors that can occur in observations. Spherical astronomy makes it easier for humans to determine the direction and position of celestial bodies relative to observers on Earth. In the history of human civilization, spherical astronomy has been the solution to determining the time of worship for medieval Muslims. Especially during the glory days of the Mamluks, Egypt and Syria. This article was written based on literature research with qualitative method as an approach. Then the collecting data was carried out by the documentation method on various notes, books, transcripts and images could be found. Then the data was analyzed descriptively. The results of this research show that Egyptian and Syrian astronomers during Mamluk reign (between the 13th-15th centuries) made a major contribution to the progress and development of science, especially in astronomy. Both the preparation of astronomical tables and various astronomical tools or instruments they designed.

Improved visualization of free-running cardiac magnetic resonance by respiratory phase using principal component analysis

Rationale and objectivesTo support cardiac MR acquisitions during breathing without ECG, we developed software to mitigate the effects of respiratory displacement of the heart. The algorithm resolves respiratory motions and cardiac cycles from DICOM files. The new software automatically detects heartbeats from expiration and inspiration to decrease apparent respiratory motion. Materials and methodsOur software uses principal component analysis to resolve respiratory motions from cardiac cycles. It groups heartbeats from expiration and inspiration to decrease apparent respiratory motion. The respiratory motion correction was evaluated on short-axis views (acquired with compressed sensing) of 11 healthy subjects and 8 cardiac patients. Two expert radiologists, blinded to the processing, assessed the dynamic images in terms of blood-myocardial contrast, endocardial interface definition, and motion artifacts. ResultsThe smallest correlation coefficients between end-systolic frames of the original dynamic scans averaged 0.79. After segregation of cardiac cycles by respiratory phase, the mean correlation coefficients between cardiac cycles were 0.94±0.03 at end-expiration and 0.90±0.08 at end-inspiration. The improvements in correlation coefficients were significant in paired t-tests for healthy subjects and heart patients at end-expiration. Clinical assessment preferred cardiac cycles during end-expiration, which maintained or enhanced scores in 90% of healthy subjects and 83% of the heart patients. Performance remained high with arrhythmia and irregular breathing present. ConclusionHeartbeats collected from end-expiration mitigate respiratory motion and are accessible by applying the new software to DICOM files from real-time CMR. Inspiratory heartbeats are also accessible for examination of arrhythmias or abnormalities at end-inspiration.

Influence of cracks on nonlinear motion of high-temperature superconducting magnetic levitation system

The magnetic levitation system of a high-temperature superconductor (HTSC) has nonlinear vibration under external excitation, in which the HTSC is subjected to a sizable electromagnetic force. The high-temperature superconducting block is a brittle material, which will crack when subject to heavy pressure. Microfracture of superconductors is inevitable, especially in superconducting magnetic levitation systems. Our paper studies the fracture behavior of a YBaCuO superconducting magnetic levitation system under a large electromagnetic force based on nonlinear bifurcated motions. The E − J constitutive model and the current vector T method are applied to obtain the electromagnetic force of the bulk superconductor during vibration. We analyze the effects of five lengths of the central crack on vibration displacements, the electric field distribution, and the electromagnetic force of superconductors. Without damages, the system does not have apparent bifurcation motion. For the inner cracks, the system has obvious bifurcation motions. The results show that the cracks have a meaningful influence on the nonlinear vibration of the superconducting magnetic levitation system. The displacement of the suspended permanent magnet in bifurcation motion increases with the increase in the crack length, and the collision occurs when the crack length reaches 15 mm.

Virtual reality—enhanced walking in people post-stroke: effect of optic flow speed and level of immersion on the gait biomechanics

BackgroundOptic flow—the apparent visual motion experienced while moving—is absent during treadmill walking. With virtual reality (VR), optic flow can be controlled to mediate alterations in human walking. The aim of this study was to investigate (1) the effects of fully immersive VR and optic flow speed manipulation on gait biomechanics, simulator sickness, and enjoyment in people post-stroke and healthy people, and (2) the effects of the level of immersion on optic flow speed and sense of presence.MethodsSixteen people post-stroke and 16 healthy controls performed two VR-enhanced treadmill walking sessions: the semi-immersive GRAIL session and fully immersive head-mounted display (HMD) session. Both consisted of five walking trials. After two habituation trials (without and with VR), participants walked three more trials under the following conditions: matched, slow, and fast optic flow. Primary outcome measures were spatiotemporal parameters and lower limb kinematics. Secondary outcomes (simulator sickness, enjoyment, and sense of presence) were assessed with the Simulator Sickness Questionnaire, Visual Analogue Scales, and Igroup Presence Questionnaire.ResultsWhen walking with the immersive HMD, the stroke group walked with a significantly slower cadence (-3.69strides/min, p = 0.006), longer stride time (+ 0.10 s, p = 0.017) and stance time for the unaffected leg (+ 1.47%, p = 0.001) and reduced swing time for the unaffected leg (− 1.47%, p = 0.001). Both groups responded to the optic flow speed manipulation such that people accelerated with a slow optic flow and decelerated with a fast optic flow. Compared to the semi-immersive GRAIL session, manipulating the optic flow speed with the fully immersive HMD had a greater effect on gait biomechanics whilst also eliciting a higher sense of presence.ConclusionAdding fully immersive VR while walking on a self-paced treadmill led to a more cautious gait pattern in people post-stroke. However, walking with the HMD was well tolerated and enjoyable. People post-stroke altered their gait parameters when optic flow speed was manipulated and showed greater alterations with the fully-immersive HMD. Further work is needed to determine the most effective type of optic flow speed manipulation as well as which other principles need to be implemented to positively influence the gait pattern of people post-stroke.Trial registration number: The study was pre-registered at ClinicalTrials.gov (NCT04521829).

Direct comparison reveals algorithmic similarities in fly and mouse visual motion detection

Evolution has equipped vertebrates and invertebrates with neural circuits that selectively encode visual motion. While similarities in the computations performed by these circuits in mouse and fruit fly have been noted, direct experimental comparisons have been lacking. Because molecular mechanisms and neuronal morphology in the two species are distinct, we directly compared motion encoding in these two species at the algorithmic level, using matched stimuli and focusing on a pair of analogous neurons, the mouse ON starburst amacrine cell (ON SAC) and Drosophila T4 neurons. We find that the cells share similar spatiotemporal receptive field structures, sensitivity to spatiotemporal correlations, and tuning to sinusoidal drifting gratings, but differ in their responses to apparent motion stimuli. Both neuron types showed a response to summed sinusoids that deviates from models for motion processing in these cells, underscoring the similarities in their processing and identifying response features that remain to be explained.

Spatiotemporal expectations of apparent motion and the effect of attentional control

An experimental investigation was conducted on whether and how temporal expectation influences visual processing in moving objects, while also considering the role of attention control. Data on reaction times were collected as outcome measures from two behavioural experiments. In experiment 1, participants (n = 36) were asked to monitor the movement of an object until its disappearance and respond quickly when it reappeared. The trajectory of an object before its disappearance generates expectations regarding the position and/or timing of its subsequent reappearance. Results revealed that all states of expectation significantly shortened reaction times compared with no expectation. In experiment 2, participants (n = 34) performed the same reaction time task while simultaneously engaging in a working memory task, which comprised memorising a string of characters. Results indicated that there is no difference in reaction times between the only temporal expectation and no expectation. Taken together, these results provide evidence to suggest that participants could predict the location and/or timing of target onset based on rhythmic moving objects, and that a secondary cognitive task impaired temporal expectation. These findings support the temporal expectation hypothesis regarding moving objects requiring attentional control resources.

The Impact of Limited Previous Motor Experience on Action Possibility Judgments in People with Spinal Muscle Atrophy.

Previous studies have shown that people with limited motor capabilities may rely on previous motor experience when making action possibility judgments for others. In the present study, we examined if having limited previous motor experience, as a consequence of spinal muscle atrophy (SMA), alters action possibility judgments. Participants with SMA and neurologically healthy (NH) sex- and age-matched controls performed a perceptual-motor judgment task using the Fitts's law paradigm. Participants observed apparent motion videos of reciprocal aiming movements with varying levels of difficulty. For each movement, participants predicted the shortest movement time (MT) at which a neurologically healthy young adult could accurately perform the task. Participants with SMA predicted significantly longer MTs compared to controls; however, the predicted MTs of both SMA and NH participants exhibited a Fitts's law relationship (i.e., the predicted MTs significantly increased as movement difficulty increased). Overall, these results provide evidence that participants with SMA who have limited, or no motor experience may make more conservative action possibility judgments for others. Critically, our finding that the pattern of action possibility judgments was not different between SMA and NH groups suggests that limited previous motor experience may not completely impair action possibility judgments.

Quantum electrodynamics of time-varying gratings

Gratings which are in apparent motion reveal some startling properties for classical radiation, especially for luminal gratings traveling at or around the speed of light. We show here that their quantum properties are even more remarkable, their effective refractive index modeling the Schwarzschild singularity which as we show generates spontaneous Hawking radiation in correlated photon pairs. Subjected to external radiation, luminal gratings provoke stimulated emission of photon pairs which we propose as a possible means of observing Hawking radiation in the laboratory.

Life motion signals bias the perception of apparent motion direction.

Walking direction conveyed by biological motion (BM) cues, which humans are highly sensitive to since birth, can elicit involuntary shifts of attention to enhance the detection of static targets. Here, we demonstrated that such intrinsic sensitivity to walking direction could also modulate the direction perception of simultaneously presented dynamic stimuli. We showed that the perceived direction of apparent motion was biased towards the walking direction even though observers had been informed in advance that the walking direction of BM did not predict the apparent motion direction. In particular, rightward BM cues had an advantage over leftward BM cues in altering the perception of motion direction. Intriguingly, this perceptual bias disappeared when BM cues were shown inverted, or when the critical biological characteristics were removed from the cues. Critically, both the perceptual direction bias and the rightward advantage persisted even when only local BM cues were presented without any global configuration. Furthermore, the rightward advantage was found to be specific to social cues (i.e., BM), as it vanished when non-social cues (i.e., arrows) were utilized. Taken together, these findings support the existence of a specific processing mechanism for life motion signals and shed new light on their influences in a dynamic environment.

A neural model of modified excitation/inhibition and feedback levels in schizophrenia.

The strength of certain visual illusions, including contrast-contrast and apparent motion, is weakened in individuals with schizophrenia. Such phenomena have been interpreted as the impaired integration of inhibitory and excitatory neural responses, and impaired top-down feedback mechanisms. To investigate whether and how these factors influence the perceived contrast-contrast and apparent motion illusions in individuals with schizophrenia, we propose a two-layer network, with top-down feedback from layer 2 to layer 1 that can model visual receptive fields (RFs) and their inhibitory and excitatory subfields. Our neural model suggests that illusion perception changes in individuals with schizophrenia can be influenced by altered top-down mechanisms and the organization of the on-center off-surround receptive fields. Alteration of the RF inhibitory surround and/or the excitatory center can replicate the difference of illusion precepts between individuals with schizophrenia within certain clinical states and normal controls. The results show that the simulated top-down feedback modulation enlarges the difference of the model illusion representations, replicating the difference between the two groups. We propose that the heterogeneity of visual and in general sensory processing in certain clinical states of schizophrenia can be largely explained by the degree of top-down feedback reduction, emphasizing the critical role of top-down feedback in illusion perception, and to a lesser extent on the imbalance of excitation/inhibition. Our neural model provides a mechanistic explanation for the modulated visual percepts of contrast-contrast and apparent motion in schizophrenia with findings that can explain a broad range of visual perceptual observations in previous studies. The two-layer motif of the current model provides a general framework that can be tailored to investigate subcortico-cortical (such as thalamocortical) and cortico-cortical networks, bridging neurobiological changes in schizophrenia and perceptual processing.

Singular Spectrum Analysis to Identify Excessive Rainfall

Indonesia is known for its excessive rainfall. Rainfall trends in an area have different characteristics. Differences in latitude, apparent motion of the sun, geographical position, topography, and the interaction of many forms of air circulation all contribute to this. Rainfall time series is essential for engineering planning, particularly for water infrastructure like irrigation, dams, urban drainage, ports, and wharves. Although meteorological technologies provide short-term rainfall predictions, long-term rainfall prediction is difficult and fraught with uncertainty. Unpredictability and seasonality can cause complex behavior in rainfall time series. This research utilizes the Singular Spectrum Analysis approach to extract trends; seasonality, cyclists, and noise can all be identified with potentially high accuracy.

Динамическое исследование кратной звезды ADS 9173 AB

Star ADS 9173=WDS 14135+5147=Hip 69483 is a complex system. The B component has a spectroscopic companion, whose orbit with a period of 4.9 years has been known since 1986. The Gaia telescope has detected a distant faint pair over 100" away from the bright AB pair. In our article, we study the movement in a bright pair based on long-term observations with the 26-inch refractor of the Pulkovo Observatory. The AB pair orbit with a period of 6306 years was calculated using the apparent motion parameters (AMP) method. The astrometric orbit of the component B was determined on the basis of the residuals of the homogeneous CCD observations up to 2023 with the 26-inch refractor. It is in agreement with the spectroscopic one. The remaining secondary residuals show a wave with a period of approximately 20 years, the reasons for which are discussed.

The speed and temporal frequency of visual apparent motion modulate auditory duration perception

In the present study, we investigated how the perception of auditory duration could be modulated by a task-irrelevant, concurrent visual apparent motion, induced by visual bars alternating between left and right sides. Moreover, we examined the influence of the speed and temporal frequency of visual apparent motion on the perception of auditory duration. In each trial, the standard visual stimuli (two vertical bars) were presented sequentially, except that visual apparent motion was included in the fourth stimulus. A tone was presented simultaneously with each visual stimulus, while the fourth tone was presented with varied duration. Participants judged whether the fourth tone lasted longer than the other four tones. In Experiment 1, the speed of visual apparent motion (Fast vs. Slow) was manipulated by changing the interval between two bars. The mean point of subjective equality (PSE) in the Slow apparent motion condition was larger than that in the Static condition. Moreover, participants tended to overestimate the duration only in the Static condition, i.e., time dilation effect, which disappeared under apparent motion conditions. In Experiment 2, in addition to speed, we controlled the temporal frequency of apparent motion by manipulating the number of bars, generating four conditions of visual apparent motion (Physical-fast, Perceived-fast, Perceived-slow, vs. Static). The mean PSE was significantly smaller in the Physical-fast condition than in the Static and Perceived-slow conditions. Moreover, we found a time compression effect in both the Perceived-slow and Static conditions but not in the Perceived-fast and Physical-fast conditions. These results suggest that the auditory duration could be modulated by the concurrent, contextual visual apparent motion, and both the speed and temporal frequency of the task-irrelevant visual apparent motion contribute to the bias in perceiving the auditory duration.

Evidence for large disturbances of the Ediacaran geomagnetic field from West Africa

Constraining the paleogeography of the Ediacaran is crucial for understanding the extensive tectonic, biological and geochemical changes that occurred during that epoch. Paleomagnetism is an essential tool for reconstructing the Ediacaran paleogeography but it is complicated because the paleomagnetic data of that age display unusually fast and large directional oscillations. Two main competing hypotheses have been proposed: the occurrence of very fast True Polar Wander (TPW) episodes, which correspond to the motion of the planetary spin axis relative to the solid Earth, or strong geomagnetic field disturbances that could potentially be dominated by an equatorial dipole field. Their implications for paleogeographic reconstructions are radically different as TPW would result in a major latitudinal shift of continents of up to ∼ 90°. In this study, we focus on one rapid paleomagnetic change recorded in pyroclastic rocks of the Ouarzazate Group in the Anti-Atlas Belt (Morocco) that has been interpreted to reflect an exceptionally fast episode of True Polar Wander between ∼ 575 and 565 Ma. To further test this hypothesis, tight constraints on the rate of the paleomagnetic directional change are needed, as TPW is speed-limited by mantle viscosity. Here, we present high-resolution Chemical Abrasion Isotope-Dilution Thermal Ionization Mass Spectrometry (CA-ID-TIMS) U-Pb dates on zircons from seven pyroclastic levels distributed stratigraphically below, in between and above the horizons where the large paleomagnetic change is observed. Based on these new data, we estimate the associated lower bound rate of the apparent polar motion related to this abrupt paleomagnetic change to be 11.6°/Myrs [5.5 – 17.9]. This value is much higher than the TPW speed limit estimated from numerical simulations, suggesting that this large paleomagnetic change cannot be explained by TPW. It could rather be associated with intense perturbations of the Ediacaran geomagnetic field potentially oscillating from an axial to an equatorial dipole. The paleomagnetic pole that we interpret as referring to the axial dipole field would imply that West Africa was located at high latitude during the mid-Ediacaran.

Astreaks: astrometry of NEOs with trailed background stars

ABSTRACT The detection and accurate astrometry of fast-moving near-Earth objects (NEOs) has been a challenge for the follow-up community. Their fast apparent motion results in streaks in sidereal images, thus affecting the telescope’s limiting magnitude and astrometric accuracy. A widely adopted technique to mitigate trailing losses is non-sidereal tracking, which transfers the streaking to background reference stars. However, no existing publicly available astrometry software is configured to detect such elongated stars. We present Astreaks, a streaking source detection algorithm, to obtain accurate astrometry of NEOs in non-sidereal data. We validate the astrometric accuracy of Astreaks on 371 non-sidereally tracked images for 115 NEOs with two instrument set-ups of the GROWTH-India Telescope. The observed NEOs had V-band magnitude in the range [15, 22] with proper motion up to 140 arcsec min−1, thus resulting in stellar streaks as high as 6.5 arcmin (582 pixels) in our data. Our method obtained astrometric solutions for all images with 100 per cent success rate. The standard deviation in observed-minus-computed (O–C) residuals is 0.52 arcsec with O–C residuals <2 arcsec (<1 arcsec) for 98.4 per cent (84.4 per cent) of our measurements. These are appreciable, given the pixel scale of ∼0.3 and ∼0.7 arcsec of our two instrument set-ups. This demonstrates that our modular and fully automated algorithm helps improve the telescope system’s limiting magnitude without compromising astrometric accuracy by enabling non-sidereal tracking on the target. This will help the NEO follow-up community cope with the accelerated discovery rates and improved sensitivity of the next-generation NEO surveys. Astreaks has been made available to the community under an open-source license.

Predictive saccades and decision making in the beetle-predating saffron robber fly.

Internal predictions about the sensory consequences of self-motion, encoded by corollary discharge, are ubiquitous in the animal kingdom, including for fruit flies, dragonflies, and humans. In contrast, predicting the future location of an independently moving external target requires an internal model. With the use of internal models for predictive gaze control, vertebrate predatory species compensate for their sluggish visual systems and long sensorimotor latencies. This ability is crucial for the timely and accurate decisions that underpin a successful attack. Here, we directly demonstrate that the robber fly Laphria saffrana, a specialized beetle predator, also uses predictive gaze control when head tracking potential prey. Laphria uses this predictive ability to perform the difficult categorization and perceptual decision task of differentiating a beetle from other flying insects with a low spatial resolution retina. Specifically, we show that (1) this predictive behavior is part of a saccade-and-fixate strategy, (2) the relative target angular position and velocity, acquired during fixation, inform the subsequent predictive saccade, and (3) the predictive saccade provides Laphria with additional fixation time to sample the frequency of the prey's specular wing reflections. We also demonstrate that Laphria uses such wing reflections as a proxy for the wingbeat frequency of the potential prey and that consecutively flashing LEDs to produce apparent motion elicits attacks when the LED flicker frequency matches that of the beetle's wingbeat cycle.

PENENTUAN AWAL WAKTU SALAT DAN ARAH KIBLAT DITINJAU DARI GERAK SEMU TAHUNAN MATAHARI

The main problem of this research is how is the existence of the apparent annual motion of the sun in determining prayer times and Qibla direction (astronomical perspective)? What is the sub-problem of the concept of the daily and annual apparent motion of the sun? and the implementation of the sun's annual apparent motion in determining the beginning of prayer times and Qibla direction?. This study uses the Library Research method, the syar'i approach and astronomy. The research results show that changes in the position of the sun cause differences in the length of day and night and affect prayer times. The difference in prayer times that changes significantly occurs when the sun's position is in the opposite direction, that is, when the sun's position is on the equinox and the equinox. Unlike the case for areas around the equator, the difference in prayer times does not change significantly. Meanwhile, determining the direction of the Qibla by the apparent annual motion of the sun, where the phenomenon when the sun culminates over the Kaaba or known as the Rashdul Qibla event which occurs on the 27th and 28th of May as well as the 15th and 16th July with the Qibla shadow can be determined at 17:18 and 17:27 WITA which occur every year. These two things prove that the apparent motion of the sun is very influential in determining the accurate start of prayer times and Qibla direction

The Effect of Annual Apparent Motion of the Sun on the Early Oscillation of Shubuh Prayer Time (Case Study of Pontianak City)

This Study aims to determine the effect of the Sun's annual apparent motion on the oscillations of the Subuh prayer time, especially in the city of Pontianak. The research method used is the literature review or reference method. In the literature review, the things that were done included: looking for the schedule of the dawn prayer in the city of Pontianak over one year, knowing the geographical position of the city of Pontianak, the apparent annual motion of the Sun, and the effect of the annual apparent motion of the Sun on the initial oscillation of the Subuh prayer time. Apart from that, another thing done in the literature review was to look for the influence of the earth-sun distance on the oscillations of the dawn prayer time. The results showed that there were similarities between the oscillations of the annual apparent motion of the Sun and the oscillations of the dawn prayer time in the city of Pontianak. However, there is a time difference with an average of 41 days between the oscillation of the Sun's annual apparent motion and the oscillation of the time of the Subuh prayer. The results of the Study also show that the distance from the Earth to the Sun (aphelion and perihelion) affects the initial oscillation of the dawn prayer time. When the Earth is at the aphelion point, the time for the Subuh prayer falls later than usual. Meanwhile, when the Earth is at perihelion, the time for the dawn prayer falls faster than usual.

Local motion signals silence the perceptual solution of global apparent motion.

Stimuli for apparent motion can have ambiguity in frame-to-frame correspondences among visual elements. This occurs when visual inputs cause a correspondence problem that allows multiple alternatives of perceptual solutions. Herein we examined the influence of local visual motions on a perceptual solution under such a multistable situation. We repeatedly alternated two frames of stimuli in a circular configuration in which discrete elements in two different colors alternated in space and switched their colors frame by frame. These stimuli were compatible with three perceptual solutions: globally consistent clockwise and counterclockwise rotations and color flickers at the same locations without such global apparent motion. We added a sinusoidal grating continuously drifting within each element to examine whether the perceptual solution for the global apparent motion was affected by the local continuous motions. We found that the local motions suppressed global apparent motion and promoted another perceptual solution that the local elements were only flickering between the two colors and drifting within static windows. It was concluded that local continuous motions as counterevidence against global apparent motion contributed to individuating visual objects and integrating visual features for maintaining object identity at the same location.

Developmental changes in visual–cognitive and attentional functions in infancy

BackgroundIdentifying developmental changes in visual-cognitive and attentional functions during infancy may lead to early diagnosis of neurodevelopmental disorders such as ASD and ADHD. AimsTo clarify the developmental changes in visual–cognitive and attentional functions during infancy (3–36 months of age). Study designCross-sectional study. SubjectsWe included 23, 24, 31, and 26 participants aged 3, 9, 18, and 36 months, respectively (full-term births). Fifteen children who cried intensely or whose data could not be accurately recorded were excluded. Outcome measuresThree activities were given to each child while they were seated in front of a gaze-tracking device to evaluate re-gaze, motion transparency, and color–motion integration. We analyzed whether the child's attention shifted to the new stimulus in their peripheral vision in the re-gaze task. In the motion transparency and color–motion integration tasks, two images were presented simultaneously on the screen. In the motion transparency task, participants preferred random dots moving in opposite directions; in the color–motion task, they preferred subjective contours from apparent motion stimuli consisting of random red and green dots with different luminance. ResultsIn the re-gaze task, fewer 3-month-olds gazed at the new target than other age groups participants. All ages showed preference for target stimuli in the motion transparency task, but 3-month-olds showed significantly lower preference in the color–motion integration task. ConclusionThese tasks may be useful for measuring visual–cognitive and attentional functions in infants.