Optometric Measurements Predict Performance but Not Comfort on a Virtual Object Placement Task With a Stereoscopic 3D Display

Twelve participants were tested on a simple virtual object precision placement task while viewing a stereoscopic 3D (S3D) display. Inclusion criteria included uncorrected or best corrected vision of 20/20 or better in each eye and stereopsis of at least 40 arc sec using the Titmus stereo test. Additionally, binocular function was assessed, including measurements of distant and near phoria (horizontal and vertical) and distant and near horizontal fusion ranges using standard optometric clinical techniques. Before each of six 30 minute experimental sessions, measurements of phoria and fusion ranges were repeated using a Keystone View Telebinocular and an S3D display, respectively. All participants completed experimental sessions in which the task required the precision placement of a virtual object in depth at the same location as a target object. Subjective discomfort was assessed using the Simulator Sickness Questionnaire (SSQ). Individual placement accuracy in S3D trials was significantly correlated with several of the binocular screening outcomes: viewers with larger convergent fusion ranges (measured at near distance), larger total fusion ranges (convergent plus divergent ranges, measured at near distance), and/or lower (better) stereoscopic acuity thresholds were more accurate on the placement task. No screening measures were predictive of subjective discomfort, perhaps due to the low levels of discomfort induced

A genetic cause of Alzheimer disease: mechanistic insights from Down syndrome

Down syndrome, caused by an extra copy of chromosome 21, is associated with a greatly increased risk of early onset Alzheimer disease. It is thought that this risk is conferred by the presence of three copies of the gene encoding amyloid precursor protein (APP), an Alzheimer risk factor, although the possession of extra copies of other chromosome 21 genes may also play a role. Further study of the mechanisms underlying the development of Alzheimer disease in Down syndrome could provide insights into the mechanisms that cause dementia in the general population

Limits to reproduction and seed size-number trade-offs that shape forest dominance and future recovery

International audienceThe relationships that control seed production in trees are fundamental to understanding the evolution of forest species and their capacity to recover from increasing losses to drought, fire, and harvest. A synthesis of fecundity data from 714 species worldwide allowed us to examine hypotheses that are central to quantifying reproduction, a foundation for assessing fitness in forest trees. Four major findings emerged. First, seed production is not constrained by a strict trade-off between seed size and numbers. Instead, seed numbers vary over ten orders of magnitude, with species that invest in large seeds producing more seeds than expected from the 1:1 trade-off. Second, gymnosperms have lower seed production than angiosperms, potentially due to their extra investments in protective woody cones. Third, nutrient-demanding species, indicated by high foliar phosphorus concentrations, have low seed production. Finally, sensitivity of individual species to soil fertility varies widely, limiting the response of community seed production to fertility gradients. In combination, these findings can inform models of forest response that need to incorporate reproductive potential

L-changing in Na(Ns, Np)-Xe collisions

A crossed atomic beam/pulsed laser technique and electric field ionization have been used to study Na(nS,nP)-Xe collisions for 28 =< n =< 52. The predominate mode for destruction of the parent nS,nP atoms is l-changing. The time evolution of the A-mixed population is monitored at several times after laser fire and fit to a rate equation to determine the rate constants for l-changing. The data can be qualitatively explained by appealing to the free electron model and applying simple energy transfer arguments to the Rydberg electron-target interaction. Present results are compared to other experimental data

Cervical transcutaneous vagal nerve stimulation (ctVNS) improves human cognitive performance under sleep deprivation stress

Lindsey McIntire et al. assess the impact of noninvasive cervical transcutaneous vagal nerve stimulation (ctVNS) on cognitive performance, mood, and attention in a cohort of sleep-deprived participants. Their results suggest that ctVNS can significantly improve arousal and multi-tasking, and may represent an alternative treatment for fatigue in humans

Visual Search Performance With 3-D Auditory Cues: Effects of Motion, Target Location, and Practice

Objectives: We evaluate visual search performance in both static (nonmoving) and dynamic (moving) search environments with and without spatial (3-D) auditory cues to target location. Additionally, the effects of target trajectory, target location, and practice are assessed. Background: Previous research on aurally aided visual search has shown a significant reduction in response times when 3-D auditory cues are displayed, relative to unaided search. However, the vast majority of this research has examined only searches for static targets in static visual environments. The present experiment was conducted to examine the effect of dynamic stimuli upon aurally aided visual search performance. Method: The 8 participants conducted repeated searches for a single visual target hidden among 15 distracting stimuli. The four main conditions of the experiment consisted of the four possible combinations of 3-D auditory cues (present or absent) and search environment (static or dynamic). Results: The auditory cues were comparably effective at reducing search times in dynamic environments (—25%) as in static environments (—22%). Audio cues helped all participants. The cues were most beneficial when the target appeared at large eccentricities and on the horizontal plane. After a brief initial exposure to 3-D audio, no training or practice effects with 3-D audio were found. Conclusion: We conclude that 3-D audio is as beneficial in environments comprising moving stimuli as in those comprising static stimuli. Application: Operators in dynamic environments, such as aircraft cockpits, ground vehicles, and command-and-control centers, could benefit greatly from 3-D auditory technology when searching their environments for visual targets or other time-critical information