Effects of gaze on vection from jittering, oscillating, and purely radial optic flow

In this study, we examined the effects of different gaze types (stationary fixation, directed looking, or gaze shifting) and gaze eccentricities (central or peripheral) on the vection induced by jittering, oscillating, and purely radial optic flow. Contrary to proposals of eccentricity independence for vection (e.g., Post, 1988), we found that peripheral directed looking improved vection and peripheral stationary fixation impaired vection induced by purely radial flow (relative to central gaze). Adding simulated horizontal or vertical viewpoint oscillation to radial flow always improved vection, irrespective of whether instructions were to fixate, or look at, the center or periphery of the self-motion display. However, adding simulated high-frequency horizontal or vertical viewpoint jitter was found to increase vection only when central gaze was maintained. In a second experiment, we showed that alternating gaze between the center and periphery of the display also improved vection (relative to stable central gaze), with greater benefits observed for purely radial flow than for horizontally or vertically oscillating radial flow. These results suggest that retinal slip plays an important role in determining the time course and strength of vection. We conclude that how and where one looks in a self-motion display can significantly alter vection by changing the degree of retinal slip

Glideslope perception during aircraft landing

Ideally, when a pilot approaches a runway on their final approach for landing, they must maintain a constant trajectory, or glideslope, of typically 3°-4°. If pilots misperceive their glideslope and alter their flight path accordingly, they are likely to overshoot or undershoot their desired touch down point on the runway. This experiment examined the accuracy of passive glideslope perceptions during simulated fixed-wing aircraft landings. 17 university students were repeatedly exposed to the following four landing scene conditions: (i) a daylight scene of a runway surrounded by buildings and lying on a 100 km deep texture mapped ground plane; (ii) a night scene with only the side runway lights visible; (iii) a night scene with the side, center, near end and far end runway lights visible and a visible horizon line; or (iv) a night scene with a runway outline (instead of discrete lights) and a visible horizon line. Each of these simulations lasted 2 seconds and represented a 130 km/hr landing approach towards a 30 m wide x 1000 m long runway with a glideslope ranging between 1° and 5°. On each experimental trial, participants viewed two simulated aircraft landings (one presented directly after the other): (a) an ideal 3° glideslope landing simulation; and (b) a comparison landing simulation, where the glideslope was either 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, or 5°. Participants simply judged which of the two landing simulations appeared to have the steepest glideslope. As expected, the daylight landing scene simulations were found to produce significantly more accurate glideslope judgments than any of the night landing simulations. However, performance was found to be unacceptably imprecise and biased for all of our landing simulation scenes. Even in daylight conditions, the smallest glideslope difference that could be reliably detected (i.e. resulted in 75% correct levels of performance) exceeded 2º for 11 of our 16 subjects. It is concluded that glideslope differences of up to 2° can not be accurately perceived based on visual information alone, regardless of scene lighting or detail. The additional visual information provided by the ground surface and buildings in the daytime significantly improved performance, however not to a level that would prevent landing incidents

Effect of decorrelation on 3-D grating detection with static and dynamic random-dot stereograms

Three experiments examined the effects of image decorrelation on the stereoscopic detection of sinusoidal depth gratings in static anddynamic random-dot stereograms (RDS). Detection was found to tolerate greater levels of image decorrelation as: (i) density increasedfrom 23 to 676 dots/deg2; (ii) spatial frequency decreased from 0.88 to 0.22 cpd; (iii) amplitude increased above 0.5 arcmin; and (iv) dotlifetime decreased from 1.6 s (static RDS) to 80 ms (dynamic RDS). In each case, the specific pattern of tolerance to decorrelation couldbe explained by its consequences for image sampling, filtering, and the influence of depth noise

Effect of decorrelation on 3-D grating detection with static and dynamic random-dot stereograms

Three experiments examined the effects of image decorrelation on the stereoscopic detection of sinusoidal depth gratings in static anddynamic random-dot stereograms (RDS). Detection was found to tolerate greater levels of image decorrelation as: (i) density increasedfrom 23 to 676 dots/deg2; (ii) spatial frequency decreased from 0.88 to 0.22 cpd; (iii) amplitude increased above 0.5 arcmin; and (iv) dotlifetime decreased from 1.6 s (static RDS) to 80 ms (dynamic RDS). In each case, the specific pattern of tolerance to decorrelation couldbe explained by its consequences for image sampling, filtering, and the influence of depth noise

Vection change exacerbates simulator sickness in virtual environments

The optic flow patterns generated by virtual reality (VR) systems typically produce visually induced experiences of self-motion (vection). While this vection can enhance presence in VR, it is often accompanied by a variant of motion sickness called simulator sickness (SS). However, not all vection experiences are the same. In terms of perceived heading and/or speed, visually simulated self-motion can be either steady or changing. It was hypothesized that changing vection would lead to more SS. Participants viewed an optic flow pattern that either steadily expanded or alternately expanded and contracted. In one experiment, SS was measured pretreatment and after 5 min of viewing using the Simulator Sickness Questionnaire. In a second experiment employing the same stimuli, vection onset and magnitude were measured using a computer-interfaced slide indicator. The steadily expandingflow pattern, compared to the expanding and contracting pattern, led to: 1) significantly less SS, 2) lower subscores for nausea, oculomotor, and disorientation symptoms, 3) more overall vection magnitude, and 4) less changing vection. Collectively, these results suggest that changing vection exacerbate SS

Vection in Depth during Consistent and Inconsistent Multisensory Stimulation

We examined vection induced during physical or simulated head oscillation along either the horizontal or depth axis. In the first two experiments, during active conditions, subjects viewed radial-flow displays which simulated viewpoint oscillation that was either in-phase or out-of-phase with their own tracked head movements. In passive conditions, stationary subjects viewed playbacks of displays generated in earlier active conditions. A third control, experiment was also conducted where physical and simulated fore ^ aft oscillation was added to a lamellar flow display. Consistent with ecology, when active in-phase horizontal oscillation was added to a radial-flow display it modestly improved vection compared to active out-of-phase and passive conditions. However, when active fore ^ aft head movements were added to either a radial-flow or a lamellar-flow display, both in-phase and out-of-phase conditions produced very similar vection. Our research shows that consistent multisensory input can enhance the visual perception of self- motion in some situations. However, it is clear that multisensory stimulation does not have to be consistent (ie ecological) to generate compelling vection in depth

The changing face of the Mediterranean: land cover, demography, and environmental change

This paper introduces a special issue on The Changing Face of the Mediterranean: Land Cover, Demography, and Environmental Change, which brings together up-to-date regional or thematic perspectives on major long-term trends in Mediterranean human–environment relations. Particularly, important insights are provided by palynology to reconstruct past vegetation and land cover, and archaeology to establish long-term demographic trends, but with further significant input from palaeoclimatology, palaeofire research and geomorphology. Here, we introduce the rationale behind this pan-Mediterranean research initiative, outline its major sources of evidence and method, and describe how individual submissions work to complement one another