A speed control law for pedestrian following based on visual angle

The allocation of perceived size and perceived motion or displacement in depth resulting from retinal size changes (changes in the visual angle of the stimulus) was investigated in situations in which all other cues of perceived changes in distance were absent. The allocation process was represented by the size-distance invariance hypothesis (SDIH), in which, for a given change in visual angle, the perceived depth was determined only by the amount of size constancy available. The changes in perceived size and perceived distance (perceived depth) were measured by kinesthetic observer (open-loop) adjustments in five situations. These situations consisted of optical expansions or contractions presented successively or simultaneously or as a mixture of successive and simultaneous presentations. The amounts of perceived motion or perceived displacement in depth obtained by kinesthetic measures were compared with those obtained from size constancy measures as applied to the SDIH. This latter measure accounted for more of the perceived depth obtained from simultaneous and mixed situations than it did for the perceived depth from the successive situations and more for the perceived depth obtained from the expansion than from the contraction situations, whether these were simultaneous or mixed. Perceived rigidity of the stimulus (perfect size constancy) clearly was not obtained in any of the situations. Significant partial size constancy and some predictive ability of the perceived sagittal motion was found using the SDIH in all the situations except in the successively presented contraction situation, with the predictive ability from the SDIH increasing with increases in the amount of size constancy. The difference between the observer's measures of the perceived motion or displacement in depth and the amount of perceived motion or displacement predicted from the perceptions of linear size using the SDIH is asserted to be due to a cognitive process associated with the perception of the different stimulus sizes as off-sized objects.

Objective The S-shaped function of probability of pedestrian fatality with respect to impact speed of vehicle is well known in road safety literature. However, the implication of this evidence for changes in speed for a population of drivers has not been explored. Method An integrated model has been developed to estimate pedestrian fatalities resulting from changes in speed of traffic. The model uses combined relative risks of injury crash rate of drivers and probability of pedestrian fatality resulting from an injury crash. Two approaches have been used—an individual approach using probability distribution of speed, and an aggregate approach, using only mean speed. The application of the model has been demonstrated using four case studies with speed of traffic before and after an intervention. Results It is found that even small reductions in mean speed translate to large reductions in pedestrian fatalities. The risk contributed by speeding vehicles is highly disproportionate to their share in vehicle population. In a case study from Delhi (India), in which at-grade junction was replaced with a grade-separated junction, 74% of risk of pedestrian fatalities is contributed by less than 5% speeding vehicles (>50km/h). Changes in mean speed is a poor indicator of changes in injury risk if the standard deviation of the distribution also changes significantly. A surprising finding was that large variation in the S-shape of pedestrian fatality risk function has relatively small effects on overall results. Conclusions A new model has been developed to estimate changes in pedestrian fatalities resulting from changes in traffic speed. The application of the model using four speed-related interventions emphasize that deterrence of a small proportion of drivers using speed enforcement can have large implications for pedestrian safety.

Gait speed is commonly used to assess walking ability in persons with stroke. Previous research related to the psychometric properties of gait speed has been conducted primarily with individuals who were able to walk independently and/or were in the later stages of recovery after stroke. The purpose of this research was to examine the test-retest reliability and minimal detectable change (MDC90) of gait speed in individuals with stroke who required varying levels of assistance to ambulate during rehabilitation. Patients who could ambulate with or without physical assistance and were undergoing inpatient rehabilitation were recruited. Gait speed was measured over the middle five meters of a nine-meter walk at a comfortable pace. Data were analyzed using the intraclass correlation coefficient (ICC2,1) and the MDC90. Thirty-five patients who were a mean 34.5 (standard deviation = 17.7) days post-stroke agreed to participate. For all the subjects combined, the ICC2,1 was 0.862 and MDC90 was 0.30 m/sec. For the 13 subjects who required physical assistance to walk, the ICC2,1 = 0.971 and MDC90 = 0.07 m/sec. For the 22 subjects who could walk without physical assistance, the ICC2,1 = 0.80 and MDC90 = 0.36 m/sec. Gait speed is a reliable measure of walking ability for a wide variety of patients undergoing rehabilitation after stroke. Gait speed is more sensitive to change in patients who require physical assistance to walk than in those who can walk without assistance. A change of more than 0.30 m/sec may be necessary in order to determine whether a change in gait speed exceeds measurement error and patient variability.

In the natural world, a number of visual cues indicate that an item is quickly approaching the perceiver. Binocular disparity is one cue for depth, and it has been demonstrated that abrupt changes in disparity, artificially unaccompanied by correlated depth cues, are capable of causing the perception of looming for the observer. An experiment involving 38 undergraduates, using a computer-controlled stereoscopic display, examined the ability of above-threshold changes in disparity (artificial looming) to facilitate response time and accuracy for observers engaged in an object-enumeration task within a cluttered display. Compared with performance using the same stimuli without disparity information (lateral motion), participants were more accurate regardless of the disparity level (9, 12, 24, or 48 minutes of arc) and faster at the two lowest levels of disparity. Participants showed the classic subitizing function, suggesting that target stimuli presented with motion information were segregated from otherwise identical distractor items. It is proposed that binocular disparity information can act as a valid location cuing method in stereoscopic computer displays in which form and color information are to be preserved.

Our aim is to develop a new generation of suprachoroidal-transretinal stimulation (STS) retinal prosthesis using a dual-stimulating electrode array to enlarge the visual field. In the present study, we aimed to examine how position and size of the visual field-created by a retinal prosthesis simulator-influenced mobility. Twelve healthy subjects wore retinal prosthesis simulators. Images captured by a web camera attached to a head-mounted display (HMD) were processed by a computer and displayed on the HMD. Three types of artificial visual fields-designed to imitate phosphenes-obtained by a single (5 × 5 electrodes; visual angle, 15°) or dual (5 × 5 electrodes ×2; visual angle, 30°) electrode array were created. Visual field (VF)1 is an inferior visual field, which corresponds to a dual-electrode array implanted in the superior hemisphere. VF2 is a superior visual field, which corresponds to a single-electrode array implanted in the inferior hemisphere. VF3 is a superior visual field, which corresponds to a dual-electrode array implanted in the inferior hemisphere. In each type of artificial visual field, a natural circular visual field (visual angle, 5°) which imitated the vision of patients with advanced retinitis pigmentosa existed at the center. Subjects were instructed to walk along a black carpet (6m long × 2.2m wide) without stepping on attached white circular obstacles. Each obstacle was 20cm in diameter, and obstacles were installed at 40-cm intervals. We measured the number of footsteps on the obstacles, the time taken to complete the obstacle course, and the extent of head movement to scan the area (head-scanning). We then compared the results recorded from these 3 types of artificial visual field. The number of footsteps on obstacles was lowest in VF3 (One-way ANOVA; P = 0.028, Fisher's LSD; VF 1 versus 3 P = 0.039, 2 versus 3 P = 0.012). No significant difference was observed for the time to complete the obstacle course or the extent of head movement between the 3 visual fields. The superior and wide visual field (VF3) obtained by the retinal prosthesis simulator resulted in better mobility performance than the other visual fields.

A stereoscope displays 2-D images with binocular disparities (stereograms), which fuse to form a 3-D stereoscopic object. But a stereoscopic object creates a conflict between vergence and accommodation. Also, motion in depth of a stereoscopic object simulated solely from change in target vergence produces anomalous motion parallax and anomalous changes in perspective. We describe a new instrument, which overcomes these problems. We call it the dichoptiscope. It resembles a mirror stereoscope, but instead of stereograms, it displays identical 2-D or 3-D physical objects to each eye. When a pair of the physical, monocular objects is fused, they create a dichoptic object that is visually identical to a real object. There is no conflict between vergence and accommodation, and motion parallax is normal. When the monocular objects move in real depth, the dichoptic object also moves in depth. The instrument allows the experimenter to control independently each of several cues to motion in depth. These cues include changes in the size of the images, changes in the vergence of the eyes, changes in binocular disparity within the moving object, and changes in the relative disparity between the moving object and a stationary object.

Do relative binocular disparities guide our movements in depth? In order to find out we asked subjects to move a 'cursor' to a target within a simulated horizontal plane at eye height. They did so by moving a computer mouse. We determined how quickly subjects responded to the target jumping in depth. We found that it took subjects about 200 ms to respond to changes in binocular disparity. Subjects responded just as quickly if the cursor was temporarily only visible to one eye near the time that the target jumped in depth, and less vigorously, though just as quickly, if the cursor jumped rather than the target, so the fastest binocular responses cannot be based directly on the relative retinal disparity between the target and the cursor. Subjects reacted faster to changes in the target's height in the visual field than to changes in binocular disparity, but did not react faster to changes in image size. These results suggest that binocular vision mainly improves people's everyday movements by giving them a better sense of the distances of relevant objects, rather than by relative retinal disparities being used to directly guide the movement. We propose that relative disparities only guide parts of very slow movements that require extreme precision.

Facebook's purchase of Oculus VR in 2014 ushered in a new era of consumer virtual reality head-mounted displays (HMDs). Converging technological advancements in small, high-resolution displays and motion-detection devices propelled VR beyond the purview of high-tech research laboratories and into the mainstream. However, technological hurdles still remain. As more consumer grade products develop, user comfort and experience will be of the utmost importance. One of the biggest issues for HMDs that lack external tracking is drift in the user position and rotation sensors. Drift can cause motion sickness and make stationary items in the virtual environment to appear to shift in position. For developers who seek to design VR experiences that are rooted in real environments, drift can create large errors in positional tracking if left uncorrected over time. Although much of the current VR hardware makes use of external tracking devices to mitigate positional and rotational drift, the creation of head-mounted displays that can operate without the use of extremal tracking devices would make VR hardware more portable and flexible, and may therefore be a goal for future development. Until technology advances sufficiently to completely overcome the hardware problems that cause drift, software solutions are a viable option to correct for it. It may be possible to speed up and slow down users as they move though the virtual world in order to bring their tracked position back into alignment with their position in the real world. If speed changes can be implemented without users noticing the alteration, it may offer a seamless solution that does not interfere with the VR experience. In Experiments 1 and 2, we artificially introduced speed changes that made users move through the VR environment either faster than or slower than their actual real-world speed. Users were tasked with correctly identifying when they were moving at the correct true-to-life speed when compared to an altered virtual movement speed. Fore and aft movement and movement from side to side initiated by seated users bending at the waist were tested separately in two experiments. In Experiment 3, we presented alternating views of the virtual scene from different user heights. In this study, users had to correctly distinguish the view of the virtual scene presented at the correct height from incorrect shorter and taller heights. In Experiments 1 and 2, we found that on average speed increases and decreases up to approximately 25% went unnoticed by users, suggesting that there is flexibility for programs to add speed changes imperceptible to users to correct for drift. In contrast, Experiment 3 demonstrates that on average users were aware of height changes after virtual heights were altered by just 5 cm. These thresholds can be used by VR developers to compensate for tracking mismatches between real and virtual positions of users of virtual environments, and also by engineers to benchmark new virtual reality hardware against human perceptual abilities.

The reliability and validity of maximal mean speed (MMS), maximal mean metabolic power (MMPmet), critical speed (CS) and critical metabolic power (CPmet) were examined throughout the 2016-2017 soccer National Youth League competitions. Global positioning system (GPS) data were collected from 20 sub-elite soccer players during a battery of maximal running tests and four home matches. A symmetric moving average algorithm was applied to the instantaneous velocity data using specific time windows (1, 5, 10, 60, 300 and 600 s) and peak values were identified. Additionally, CS and CP¬met values calculated from match data were compared to CS and CPmet values determined from previously validated field tests to assess the validity of match values. Intra-class correlation (one-way random absolute agreement) scores ranged from 0.577 to 0.902 for speed, and from 0.701 to 0.863 for metabolic power values. Coefficients of variation (CV) ranged from good to moderate for speed (4-6%) and metabolic power (4-8%). Only CS and CPmet values were significantly correlated (r = 0.842; 0.700) and not statistically different (p = 0.066; 0.271) to values obtained in a shuttle-running critical test. While the present findings identified match-derived MMS, MMPmet, CS and CPmet to be reliable, only CS and CPmet derived from match play were validated to a CS field test that required changes in speed and direction rather than continuous running. This suggests that both maximal mean and critical speed and metabolic power analyses could be alternatives to absolute distance and speed in the assessment of match running performance during competitive matches.

To the Editor. —I studied with interest the equation by Drs Holladay and Prager 1 published in the July 1989Archives. Their equation, Snellen Acuity = 20 × 10 [(55 - X)/50] , converts the number of letters read correctly from the Bailey-Lovie acuity chart 2 into the denominator of the Snellen fraction for the reference distance 20 ft. The formula, which relates the base 10 to the exponential denominator 50, echoes the design of the chart, which is based on a 10-fold change in visual angle for each 50 letters (10 lines). I propose a modified equation, whereby dropping the constant 20 and taking the reciprocal yields, Snellen Acuity = 10 -[(55 - X)/50] , (1) where X is the number of letters read correctly from the chart. This yields Snellen acuity directly in its decimal form, which may be more useful for certain statistical analyses. Equation 1 is approximately, but not exactly, equivalent to

Influence of binocular disparity changes on the crowding effect

Physical inactivity is associated with elevated risks for many chronic diseases and premature death. Both rodent and human studies indicate that sex steroids—testosterone and estrogen—play a role in the biological regulation of physical activity. The sex steroids likely affect brain physiology and/or the cellular condition of the skeletal muscle of the hind limb muscles used to complete a wheel running task. Differences in speed patterns between physiologically different sex steroid levels may indicate a deficiency in the skeletal muscle's capability to effectively contract during wheel running, while differences in the accumulated duration pattern during wheel running may indicate a deficiency in central motivation to complete a prolonged wheel running bout. The purpose of this study was to assess wheel running speed and duration patterns in male C57BL/6J mice under normal and physiologically‐deficient testosterone conditions. Wheel running data were collected for ten days (n=14 physiologically normal; n=12 testosterone deficient) and each wheel revolution was counted and time‐stamped to accumulate a daily turn‐by‐turn wheel revolution record. Testosterone deficiency was induced via bilateral orchidectomy ten‐days prior to wheel running assessment. Ten‐day average speed (m·min−1) and accumulated duration (% of total activity during the dark period) were assessed in four 3‐hour epochs during the dark period (epoch 1: 6pm–9pm, epoch 2: 9pm–12am, epoch 3: 12am–3am, epoch 4: 3am–6am). Differences in speed and duration data across epochs and between treatment groups were compared by separate 4 × 2 mixed‐design ANOVAs. Wheel running speed was significantly [F(3,72)=6.5, p=0.001] different across epochs and between treatments. Wheel running speed remained consistent across all epochs in intact mice but decreased from a zenith during the initial epoch (mean±sd: 30.1±5.0 m·min−1) to a nadir (26.9±3.8 m·min−1) in deficient animals during the latter epochs. Intact mice ran faster (31.4±2.8 m·min−1) than deficient mice (26.1±5.4 m·min−1) throughout the dark period as a whole. Wheel running duration was significantly [F(3,72)=28.8, p<0.001] different across epochs and between treatments. The intact mice recorded higher percentages of wheel running during the initial epoch and decreased as the dark period progressed. Testosterone deficient mice ran the most (highest percentages) during the first and last epochs. In conclusion, wheel running patterns were significantly different following alteration to circulating testosterone levels in male mice. Changes in speed and duration patterns during wheel running indicate that both brain physiology and the cellular composition of skeletal muscle may be affected by the loss of testosterone.Support or Funding InformationThis project was supported by the Pilgram Marpeck School of STEM intramural research fund at Truett McConnell University.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Squash is an indoor game that is the second fastest racket sports if compared to badminton and tennis. Squash game puts a high demand on physical fitness of elite players which requires a quick development of high force, rapid changes of direction and fast reaction. The objective of this study was to develop the physical fitness profile of Malaysian junior state squash players. Sixty five 10 to 18 years old male Kelantan state squash players were tested with seven skill-related fitness tests. SPSS version 20.0 was used to analyze the data collected from the tests. A one-way ANOVA was used to detect statistical differences between groups. A posthoc test (LSD) was performed to determine differences in in the variables between groups. The data was collected for flexibility, speed, muscular endurance, power of upper and lower extremities, agility and cardiovascular endurance. There were significant differences in the mean speed, muscular endurance, agility, power of lower extremities, power of upper extremities, flexibility and predicted VO 2 max between 13-15 and 16-18 years of age groups when compared to 10-12 years old players (p<0.05). Similarly, there were significant differences in speed, muscular endurance, agility, power of lower extremities, power of upper extremities, flexibility and VO 2 max between 16-18 and 13-15 year old players (p<0.05).

Adaptation to Natural Binocular Disparities in Primate V1 Explained by a Generalized Energy Model

Abstract.Food resources and water flow speeds vary on short‐temporal and small‐spatial scales important to feeding in natural populations of oysters (Crassostrea virginica). To better describe food availability to the oyster population, micro‐current meters were used to measure flow 1–3 cm above the bottom and frequent water sampling was used to determine the quantity and composition of the seston on Confederate Reef, Galveston Bay, Texas. The quantity and quality of food varied on time scales at least as short as 3 h and throughout the water column. Seston was high in detrital carbon, nitrogen poor, and had a high fraction of inorganic particles. The quantity of food at the bed was not predictable from samples taken near the surface. Water flow speeds were also highly variable. Whereas rapid flow speeds were measured, flow speed tended to cluster about a narrower range of slower speeds resulting in the mean speed being much higher than the median. Fluxes of food calculated from the quantity of food and water flow speeds were low and highly variable. Under most conditions, water flow speed was more important than food quantity in determining flux. Rapid flow rates could overcome low food quantity to result in relatively high fluxes, whereas slow flow resulted in small fluxes even if food was abundant. Changes in water flow rate associated with tidal changes and changes in speed are probably the primary agents controlling food availability on a daily basis. Decreased wind speed at night normally reduced flux in the early morning hours, for example. These results stress the importance of measuring food quantity and water flow speed on spatial and temporal scales important to oyster feeding. Model simulations of oyster populations at varying densities, flow rates and clump heights across the range of measured values show that flow rate is insufficient during most hours of the day and days of the year to prevent oysters from locally reducing food supply by their filtering efforts. Thus flow rate probably limits population density and adult size on Confederate Reef.