Coexisting Pulses in a Model for Binary-Mixture Convection

We address the striking coexistence of localized waves (`pulses') of different lengths which was observed in recent experiments and full numerical simulations of binary-mixture convection. Using a set of extended Ginzburg-Landau equations, we show that this multiplicity finds a natural explanation in terms of the competition of two distinct, physical localization mechanisms; one arises from dispersion and the other from a concentration mode. This competition is absent in the standard Ginzburg-Landau equation. It may also be relevant in other waves coupled to a large-scale field.Comment: 5 pages revtex with 4 postscript figures (everything uuencoded

Pattern Selection in the Complex Ginzburg-Landau Equation with Multi-Resonant Forcing

We study the excitation of spatial patterns by resonant, multi-frequency forcing in systems undergoing a Hopf bifurcation to spatially homogeneous oscillations. Using weakly nonlinear analysis we show that for small amplitudes only stripe or hexagon patterns are linearly stable, whereas square patterns and patterns involving more than three modes are unstable. In the case of hexagon patterns up- and down-hexagons can be simultaneously stable. The third-order, weakly nonlinear analysis predicts stable square patterns and super-hexagons for larger amplitudes. Direct simulations show, however, that in this regime the third-order weakly nonlinear analysis is insufficient, and these patterns are, in fact unstable

Point-to-origin experiments in VR revealed novel qualitative errors in visual path integration

Even in state-of-the-art virtual reality (VR) setups, participants often feel lost when navigating through virtual environments. In psychological experiments, such disorientation is often compensated for by extensive training and performance feedback. The current study investigated participants' sense of direction by means of a rapid point-to-origin task without any training or performance feedback. This allowed us to study participants' intuitive spatial orientation processes in VR while minimizing the influence of higher cognitive abilities and compensatory strategies. From an applied perspective, such a paradigm could be employed for evaluating the effectiveness and usability of a given VR setup for enabling natural and unencumbered spatial orientation even for first-time users, which is important for tasks such as architecture walk-throughs, evacuation scenario training, or driving/flight simulators

Physical self-motion facilitates object recognition, but does not enable view-independence

It is well known that people have difficulties in recognizing an object from novel views as compared to learned views, resulting in increased response times and/or errors. This so-called view-dependency has been confirmed by many studies. In the natural environment, however, there are two ways of changing views of an object: one is to rotate an object in front of a stationary observer (object-movement), the other is for the observer to move around a stationary object (observer-movement). Note that almost all previous studies are based on the former procedure. Simons et al. [2002] criticized previous studies in this regard and examined the difference between object- and observer-movement directly. As a result, Simons et al. [2002] reported the elimination of this view-dependency when novel views resulted from observer-movement, instead of object-movement. They suggest the contribution of extra-retinal (vestibular and proprioceptive) information to object recognition. Recently, however, Zhao et al. [2007] repor ted that the observeramp;amp;lsquo;s movement from one view to another only decreased view-dependency without fully eliminating it. Furthermore, even this effect vanished for rotations of 90° instead of 50°. Larger rotations were not tested. The aim of the present study was to clarify the underlying mechanism of this phenomenon and to investigate larger angles of view change (45-180°, in 45° steps)

The search for instantaneous vection: An oscillating visual prime reduces vection onset latency

2018 Palmisano, Riecke. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Typically it takes up to 10 seconds or more to induce a visual illusion of self-motion ( vection ). However, for this vection to be most useful in virtual reality and vehicle simulation, it needs to be induced quickly, if not immediately. This study examined whether vection onset latency could be reduced towards zero using visual display manipulations alone. In the main experiments, visual self-motion simulations were presented to observers via either a large external display or a head-mounted display (HMD). Priming observers with visually simulated viewpoint oscillation for just ten seconds before the main self-motion display was found to markedly reduce vection onset latencies (and also increase ratings of vection strength) in both experiments. As in earlier studies, incorporating this simulated viewpoint oscillation into the self-motion displays themselves was also found to improve vection. Average onset latencies were reduced from 8-9s in the no oscillating control condition to as little as 4.6 s (for external displays) or 1.7 s (for HMDs) in the combined oscillation condition (when both the visual prime and the main self-motion display were oscillating). As these display manipulations did not appear to increase the likelihood or severity of motion sickness in the current study, they could possibly be used to enhance computer generated simulation experiences and training in the future, at no additional cost

Phase Diffusion in Localized Spatio-Temporal Amplitude Chaos

We present numerical simulations of coupled Ginzburg-Landau equations describing parametrically excited waves which reveal persistent dynamics due to the occurrence of phase slips in sequential pairs, with the second phase slip quickly following and negating the first. Of particular interest are solutions where these double phase slips occur irregularly in space and time within a spatially localized region. An effective phase diffusion equation utilizing the long term phase conservation of the solution explains the localization of this new form of amplitude chaos.Comment: 4 pages incl. 5 figures uucompresse

Attractive Interaction Between Pulses in a Model for Binary-Mixture Convection

Recent experiments on convection in binary mixtures have shown that the interaction between localized waves (pulses) can be repulsive as well as {\it attractive} and depends strongly on the relative {\it orientation} of the pulses. It is demonstrated that the concentration mode, which is characteristic of the extended Ginzburg-Landau equations introduced recently, allows a natural understanding of that result. Within the standard complex Ginzburg-Landau equation this would not be possible.Comment: 7 pages revtex with 3 postscript figures (uuencoded

Measuring Vection in a Large Screen Virtual Environment

This paper describes the use of a large screen virtual environment to induce the perception of translational and rotational self-motion. We explore two aspects of this problem. Our first study investigates how the level of visual immersion (seeing a reference frame) affects subjective measures of vection. For visual patterns consistent with translation, self-reported subjective measures of self-motion were increased when the floor and ceiling were visible outside of the projection area. When the visual patterns indicated rotation, the strength of the subjective experience of circular vection was unaffected by whether or not the floor and ceiling were visible. We also found that circular vection induced by the large screen display was reported subjectively more compelling than translational vection. The second study we present describes a novel way in which to measure the effects of displays intended to produce a sense of vection. It is known that people unintentionally drift forward if asked to run in place while blindfolded and that adaptations involving perceived linear self-motion can change the rate of drift. We showed for the first time that there is a lateral drift following perceived rotational self-motion and we added to the empirical data associated with the drift effect for translational self-motion by exploring the condition in which the only self-motion cues are visual

Reicht optischer Fluß wirklich nicht zum Heimfinden?

Die Literatur legt nahe, daß selbst für einfache Orientierungs- und Heimfindeaufgaben die durch optischen Fluß gegebene Information unzureichend ist und vestibuläre und kinästhetische Reize benötigt werden. Um diese Behauptung zu testen, führten wir Dreiecksvervollständigungsexperimente in einer virtuellen Umgebung durch, die als einzige Informationsquelle optischen Fluß anbot. Die simulierte Eigenbewegung wurden visuell auf einer halbzylindrischen 180° Projektionsleinwand (7m Durchmesser) dargeboten und über Maus-Tasten gesteuert. Damit die Versuchspersonen zur Navigation nur Pfadintegration und keine Landmarkeninformation verwenden konnten, bestand die simulierte Welt lediglich aus einer 3D Punktewolke. Diese enthielt keinerlei hilfreiche Orientierungspunkte (Landmarken), vermittelte jedoch ein überzeugendes Gefühl von Eigenbewegung (Vektion). In Exp 1 sollten die Versuchspersonen Drehungen um bestimmte Winkel ausführen sowie Distanzen reproduzieren, wobei die Geschwindigkeiten randomisiert wurden. Exp 2 3 waren Dreiecksvervollständigungsexperimente: Versuchspersonen folgten zwei Schenkeln eines Dreiecks und sollten dann selbstständig zum nicht markierten Ausgangspunkt zurückfinden. In Exp 2 wurden fünf verschiedene gleichschenklige Dreiecke für Links- und Rechtsdrehungen verwendet, in Exp 3 hingegen 60 verschiedene Dreiecke mit randomisierten Schenkellängen und Winkeln. Unabhängig von der Bewegungsgeschwindigkeit konnten untrainierte Versuchspersonen in Exp 1 Drehungen und Distanzen mit nur geringfügigem systematischen Fehler ausführen. Wir fanden in Exp 2 3 generell eine lineare Korrelation zwischen ausgeführten und korrekten Werten für die Meßgrößen Drehwinkel und zurückgelegte Distanz. Für die weitere Analyse verwendeten wir deshalb für beide Meßgrößen die Steigungen der Regressionsgeraden (“Kompressionsrate”) und die Abweichungen vom korrekten Wert (signed error). Exp 2 zeigte keine signifikanten Fehler (d.h. generelle Über- oder Unterschätzung) für Drehungen oder Distanzen. Distanzantworten waren stark in Richtung Mittelwert verschoben (Kompressionsrate 0.58), Winkelantworten jedoch kaum (0.91). Für randomisierte Dreiecksgeometrien in Exp 3 reduzierte sich diese Tendenz zu mittleren Antworten für Distanzen (0.86), verstärkte sich jedoch für Drehungen (0.77). In ähnlichen Experimenten zur Dreiecksvervollständigung unter Beschränkung auf visuelle Information (Virtual Reality: Péruch et al., Perc. ‘97; Duchon et al., Psychonomics ‘99) und auf propriozeptive Reize (blindes gehen: Loomis et al., JEP ‘93) zeigte sich eine starke Tendenz zu mittleren Drehwinkeln (Kompressionsrate < 0.5), die wir nicht fanden. Die Tendenz, bei reinen Drehaufgaben in visuellen virtuellen Umgebungen nicht weit genug zu drehen (Péruch ‘97; Bakker, Presence ‘99) konnte ebenfalls nicht beobachtet werden (Exp 1). Pfadintegration aufgrund optischen Flusses erwies sich in unseren Experimenten als ausreichend und verläßlich für Orientierungs- und Heimfindeaufgaben. Vestibuläre und kinästhetische Information waren hierfür nicht erforderlich

Visually induced linear vection is enhanced by small physical accelerations

Wong & Frost (1981) showed that the onset latency of visually induced self-rotation illusions (circular vection) can be reduced by concomitant small physical motions (jerks). Here, we tested whether (a) such facilitation also applies for translations, and (b) whether the strength of the jerk (degree of visuo-vestibular cue conflict) matters. 14 naïve observers rated onset, intensity, and convincingness of forward linear vection induced by photorealistic visual stimuli of a street of houses presented on a projection screen (FOV: 75°×58°). For 2/3 of the trials, brief physical forward accelerations (jerks applied using a Stewart motion platform) accompanied the visual motion onset. Adding jerks enhanced vection significantly; Onset latency was reduced by 50, convincingness and intensity ratings increased by more than 60. Effect size was independent of visual acceleration (1.2 and 12m/s^2) and jerk size (about 0.8 and 1.6m/s^2 at participants’ head for 1 and 3cm displacement, respectively), and showed no interactions. Thus, quantitative matching between the visual and physical acceleration profiles might not be as critical as often believed as long as they match qualitatively and are temporally synchronized. These findings could be employed for improving the convincingness and effectiveness of low-cost simulators without the need for expensive, large motion platforms