Space Perception in Virtual Environments: Displacement from the Center of Projection Causes Less Distortion than Predicted by Cue-Based Models

Virtual reality systems commonly include both monocular and binocular depth cues, which have the potential to provide viewers with a realistic impression of spatial properties of the virtual environment. However, when multiple viewers share the same display, only one viewer typically receives the projectively correct images. All other viewers experience the same images despite displacement from the center of projection (CoP). Three experiments evaluated perceptual distortions caused by displacement from the CoP and compared those percepts to predictions of models based on monocular and binocular viewing geometry. Leftward and rightward displacement from the CoP caused virtual angles on the ground plane to be judged as larger and smaller, respectively, compared to judgments from the CoP. Backward and forward displacement caused rectangles on the ground plane to be judged as larger and smaller in depth, respectively, compared to judgments from the CoP. Judgment biases were in the same direction as cue-based model predictions but of smaller magnitude. Displacement from the CoP had asymmetric effects on perceptual judgments, unlike model predictions. Perceptual distortion occurred with monocular cues alone but was exaggerated when binocular cues were added. The results are grounded in terms of practical implications for multiuser virtual environments

An ancient adaptive episode of convergent molecular evolution confounds phylogenetic inference

Convergence can mislead phylogenetic inference by mimicking shared ancestry, but has been detected only rarely in molecular evolution. Here, we show that significant convergence occurred in snake and agamid lizard mitochondrial genomes. Most evidence, and most of the mitochondrial genome, supports one phylogenetic tree, but a subset of mostly amino acid-altering mitochondrial sites strongly support a radically different phylogeny. These sites are convergent, probably selected, and overwhelm the signal from other sites. This suggests that convergent molecular evolution can seriously mislead phylogenetics, even with large data sets. Radical phylogenies inconsistent with previous evidence should be treated cautiously

Diagnosing perceptual distortion present in group stereoscopic viewing

Stereoscopic displays are an increasingly prevalent tool for experiencing virtual environments, and the inclusion of stereo has the potential to improve distance perception within the virtual environment. When multiple users simultaneously view the same stereoscopic display, only one user experiences the projectively correct view of the virtual environment, and all other users view the same stereoscopic images while standing at locations displaced from the center of projection (CoP). This study was designed to evaluate the perceptual distortions caused by displacement from the CoP when viewing virtual objects in the context of a virtual scene containing stereo depth cues. Judgments of angles were distorted after leftward and rightward displacement from the CoP. Judgments of object depth were distorted after forward and backward displacement from the CoP. However, perceptual distortions of angle and depth were smaller than predicted by a ray-intersection model based on stereo viewing geometry. Furthermore, perceptual distortions were asymmetric, leading to different patterns of distortion depending on the direction of displacement. This asymmetry also conflicts with the predictions of the ray-intersection model. The presence of monocular depth cues might account for departures from model predictions

Statistical Study of the Properties of Magnetosheath Lion Roars

Lion roars are narrowband whistler wave emissions that have been observed in several environments, such as planetary magnetosheaths, the Earth's magnetosphere, the solar wind, downstream of interplanetary shocks, and the cusp region. We present measurements of more than 30,000 such emissions observed by the Magnetospheric Multiscale spacecraft with high‐cadence (8,192 samples/s) search coil magnetometer data. A semiautomatic algorithm was used to identify the emissions, and an adaptive interval algorithm in conjunction with minimum variance analysis was used to determine their wave vector. The properties of the waves are determined in both the spacecraft and plasma rest frame. The mean wave normal angle, with respect to the background magnetic field (B0), plasma bulk flow velocity (Vb), and the coplanarity plane (Vb×B0) are 23°, 56°, and 0°, respectively. The average peak frequencies were ∼31% of the electron gyrofrequency (ωce) observed in the spacecraft frame and ∼18% of ωce in the plasma rest frame. In the spacecraft frame, ∼99% of the emissions had a frequency <ωce, while 98% had a peak frequency <0.72ωce in the plasma rest frame. None of the waves had frequencies lower than the lower hybrid frequency, ω. From the probability density function of the electron plasma βe, the ratio between the electron thermal and magnetic pressure, ∼99.6% of the waves were observed with βe<4 with a large narrow peak at 0.07 and two smaller, but wider, peaks at 1.26 and 2.28, while the average value was ∼1.25

Creating a flexible LVC architecture for mixed reality training of the dismounted warfighter

Physical military training within military operations in urban terrain (MOUT) environments provides a realistic experience, albeit at high cost and limited scenario flexibility. Alternatively, training within serious games, often from a laptop, provides a low cost, highly flexible platform, but lacks sufficient realism and engagement for some applications. Live, virtual, and constructive (LVC) systems attempt to combine these two and capitalize on their strengths for joint forces training. However, current LVC training environments for the dismounted warfighter often are too small for realistic squad-sized training, constructed statically without ability to reconfigure quickly into new scenarios, are developed as standalone systems dependent on specific communication protocols, and do not enable realistic interaction between LVC entities. In response to these challenges, a rapidly reconfigurable LVC training system was developed at Iowa State University, known as the Veldt. The physical Veldt environment consists of a 44`x60' room with modular walls configured in unique layouts for different training scenarios. These configurations contain doorways, windows, alleys and other openings, which may contain displays rendering the virtual environment for seamless integration between the physical and virtual worlds. A tracking system gathers position and orientation information on trainees, weapons and other objects and a clustered game engine then uses this information to create virtual representations of the trainees in the virtual world. This information is sent through a communication server which distributes it to other connected components such as game engines and simulations which populate the virtual world with live and constructive entities. This thesis presents solutions to two key challenges in creation of the Veldt: 1) how to correlate all physical and virtual worlds for seamless interaction regardless of location and 2) how to design a network architecture that is easily extendable and can accommodate multiple protocol types. The correlation of physical and virtual worlds is necessary for entities, their models, and terrain. A central communication architecture became the first element of a solution by flexibly connecting entities' location, orientation, fire and other information without requiring individual connections between all components. To enable appropriate collaboration between LVC trainees within the system, models must be visually indistinguishable regardless of interaction medium. However, most game engine and simulations contain separate, sometimes proprietary, model databases. A model-matching approach was applied to overcome this challenge, requiring only minor configuration of connected components for a set of common models common to all the components' databases. This approach resulted in a less extensive, non-identical common database, but is more easily scalable and requires less resources over other methods. Terrain correlation is required to prevent issues with collaboration and fair fight between distributed LVC entities, where improper terrain correlation could create an unrealistic training environment. Similar to model database correlation, game engine and simulation systems typically contain separate, sometimes proprietary terrains and terrain formats. Because utilizing separate tools to convert from a single source into different formats often produces non-identical terrains, a single procedural terrain modeling framework was created and implemented for the Veldt system. The solution to the second challenge of creating a protocol independent network architecture was achieved by processing the entity information flowing through a central communication server. With this design, the communication server receives information from one component in its native protocol, converts that into a world state, and then for all interested components, converts the world state into a component's native protocol and sends the information. Therefore, the communication server only requires packing and unpacking methods to and from a world state to easily extend the network architecture to include other protocols. These methods were first evaluated within a user study conducted by the Research Institute for Studies in Education (RISE) at Iowa State University. The study results found high ratings of the system by participants on involvement, interaction, and immersion; indicating a near seamless physical-virtual correlation between environments. A interservice demonstration of the system involving many distributed components and multiple live, virtual, and constructive entities provided further evaluation. The successfulness of this demonstration, involving collaboration between participants in live and virtual environments, further proved the successful correlation of the physical and virtual worlds. In addition, the demonstration proved success of the protocol independent network architecture, as the scenario ran in real-time with negligible latency and with two differing protocols types.</p

The Right View from the Wrong Location: Depth Perception in Stereoscopic Multi-User Virtual Environments

Stereoscopic depth cues improve depth perception and increase immersion within virtual environments (VEs). However, improper display of these cues can distort perceived distances and directions. Consider a multi-user VE, where all users view identical stereoscopic images regardless of physical location. In this scenario, cues are typically customized for one "leader" equipped with a head-tracking device. This user stands at the center of projection (CoP) and all other users ("followers") view the scene from other locations and receive improper depth cues. This paper examines perceived depth distortion when viewing stereoscopic VEs from follower perspectives and the impact of these distortions on collaborative spatial judgments. Pairs of participants made collaborative depth judgments of virtual shapes viewed from the CoP or after displacement forward or backward. Forward and backward displacement caused perceived depth compression and expansion, respectively, with greater compression than expansion. Furthermore, distortion was less than predicted by a ray-intersection model of stereo geometry. Collaboration times were significantly longer when participants stood at different locations compared to the same location, and increased with greater perceived depth discrepancy between the two viewing locations. These findings advance our understanding of spatial distortions in multi-user VEs, and suggest a strategy for reducing distortion.This is a manuscript of an article published as Pollock, Brice, Melissa Burton, Jonathan W. Kelly, Stephen Gilbert, and Eliot Winer. "The right view from the wrong location: Depth perception in stereoscopic multi-user virtual environments." IEEE Transactions on Visualization and Computer Graphics 18, no. 4 (2012): 581-588. DOI: 10.1109/TVCG.2012.58. Posted with permission.</p

Suicidality and protective factors among sexual and gender minority youth and adults in Canada: a cross-sectional, population-based study

Abstract Background Sexual and gender minority populations experience elevated risks for suicidality. This study aimed to assess prevalence and disparities in non-fatal suicidality and potential protective factors related to social support and health care access among sexual and gender minority youth and adults and their heterosexual and cisgender counterparts in Canada. The second objective was to examine changes in the prevalence of suicidal ideation and protective factors during the COVID-19 pandemic. Methods Pooled data from the 2015, 2016 and 2019 Canadian Community Health Surveys were used to estimate pre-pandemic prevalence of suicidal ideation, plans and attempts, and protective factors. The study also estimated changes in the prevalence of recent suicidal ideation and protective factors in fall 2020, compared with the same period pre-pandemic. Results The prevalence of suicidality was higher among the sexual minority populations compared with the heterosexual population, and the prevalence was highest among the bisexual population, regardless of sex or age group. The pre-pandemic prevalence of recent suicidal ideation was 14.0% for the bisexual population, 5.2% for the gay/lesbian population, and 2.4% for the heterosexual population. The prevalence of lifetime suicide attempts was 16.6%, 8.6%, and 2.8% respectively. More than 40% of sexual minority populations aged 15–44 years had lifetime suicidal ideation; 64.3% and 36.5% of the gender minority population had lifetime suicidal ideation and suicide attempts. Sexual and gender minority populations had a lower prevalence of protective factors related to social support and health care access. The prevalence of recent suicidal ideation among sexual and gender minority populations increased in fall 2020, and they tended to experience longer wait times for immediate care needed. Conclusions Sexual and gender minority populations had a higher prevalence of suicidality and less social support and health care access compared to the heterosexual and cisgender populations. The pandemic was associated with increased suicidal ideation and limited access to care for these groups. Public health interventions that target modifiable protective factors may help decrease suicidality and reduce health disparities

My Man

Gift of Dr. Mary Jane Esplen.Piano vocal guitar [instrumentation]G major [key]Moderato de Schottisch espagnole [tempo]Popular song [form/genre]Decorative [illustration]Publisher's advertisement on front inside cover & back cover [note]Reprint [note

Diagnosing perceptual distortion present in group stereoscopic viewing

Stereoscopic displays are an increasingly prevalent tool for experiencing virtual environments, and the inclusion of stereo has the potential to improve distance perception within the virtual environment. When multiple users simultaneously view the same stereoscopic display, only one user experiences the projectively correct view of the virtual environment, and all other users view the same stereoscopic images while standing at locations displaced from the center of projection (CoP). This study was designed to evaluate the perceptual distortions caused by displacement from the CoP when viewing virtual objects in the context of a virtual scene containing stereo depth cues. Judgments of angles were distorted after leftward and rightward displacement from the CoP. Judgments of object depth were distorted after forward and backward displacement from the CoP. However, perceptual distortions of angle and depth were smaller than predicted by a ray-intersection model based on stereo viewing geometry. Furthermore, perceptual distortions were asymmetric, leading to different patterns of distortion depending on the direction of displacement. This asymmetry also conflicts with the predictions of the ray-intersection model. The presence of monocular depth cues might account for departures from model predictions.This is a conference proceeding from Proceedings of SPIE 8291 (2012): 1, doi:10.1117/12.912184. Posted with permission. Copyright 2012 Society of Photo-Optical Instrumentation Engineers. One print or electronic copy may be made for personal use only. Systematic electronic or print reproduction and distribution, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper are prohibited.</p