Th. Brandt

Differential effects of central versus peripheral vision on egocentric and exocentric motion perception

SummaryOptokinetic stimuli allow for two perceptual interpretations. The observer may perceive himself as being stationary in a moving surround (egocentric motion perception) or he may experience an illusion of self-motion, so that the actually moving surroundings appear to be stable (exocentric motion perception).Results1.Circular motion of the entire surroundings (rotating drum) invariably leads to an apparent self-rotation (circularvection: CV), which is indistinguishable from an actual chair rotation.2.Following stimulus onset, CV begins after a few seconds latency and slowly increases its apparent velocity until its saturation. CV may outlast the visual stimulus by as much as 30 sec. Latencies are independent of stimulus velocity.3.Even with drum accelerations up to 15°/sec2, stationary subjects cannot infer from the lack of vestibular input that only the drum is rotating.4.With stimulation of the entire visual field or sufficiently large parts of the peripheral retina, the velocity of apparent self-rotation matches stimulus speed up to 90–120°/sec. At higher speeds, CV velocity lags behind stimulus speed and results in additional egocentric motion perception.5.Masking the central visual field by black disks up to 120° in diameter scarcely diminishes CV. Conversely, if peripheral vision is precluded, stimulation of the central field up to 30° in diameter results in exclusive egocentric motion perception of the surround. With a central and peripheral stimulus equivalent in area, the peripheral stimulus predominates CV.6.Simultaneous presentation of conflicting central and peripheral optokinetic stimuli (i.e., stimuli rotating in opposite directions) has shown that exocentric orientation depends on the peripheral stimulus whereas optokinetic nystagmus and egocentric motion perception rely on the center of the visual field.

Motion habituation: inverted self-motion perception and optokinetic after-nystagmus.

SummaryThe oculomotor and perceptual after-effects (AE) of optokinetic motion stimulation as well as the adaptive changes during stimulation were studied. The intensity and duration of optokinetic after-nystagmus (OKAN) and self-motion after-sensation (CV) are a function of stimulus duration. The direction is a result of two competing processes: positive tonus continuing the actual response to the stimulus and negative tonus causing a reversal in direction. Positive AEs increase with stimulus durations up to 1 min; the negative AEs increase up to the longest stimulus duration tested (15 min) and by antagonizing the positive AEs shorten their duration once stimulus duration exceeds 3 min. Negative AEs are interpreted as the consequence of a central counter-regulation to the actual stimulus effects: motion habituation.During prolonged stimulation, motion habituation causes an apparent decrease in perceived velocity and may result in the sensation of periodic reversals of the direction of perceived self-motion, concurrent with a shift in average eye position towards the direction of the apparent reversal of self-motion, i.e. the nystagmic “Schlagfeld” reverses from the normal rapid-phase-side to the slow-phase as does also the CV.Oculomotor and perceptual AEs similarly depend on stimulus qualities (e.g. duration, area of the moving stimulus and its location in the visual field). It is argued that positive AEs are due to an imbalance induced in the vestibular nuclei by the stimulus, and it is hypothezised that motion habituation acts upon the vestibular nuclei.

The spatial frequency effect on perceived velocity

Abstract The effect of the spatial frequency of a vertically oriented, horizontally moving stripe pattern on perceived speed was investigated. Perceived velocity increased linearly with both angular speed and spatial frequency. The spatial frequency effect was independent of the relative angular width of light and dark stripes and was also found to apply to the case of a single moving bar. Evidence for weighted frequency averaging was obtained for more complex patterns. The results are consistent with a model involving both a spatial frequency dependent input mediated by temporal frequency and an angular speed input relating to the movement of a single edge through the visual field.

Arthrokinetic nystagmus and ego-motion sensation

SummaryA compelling illusion of body rotation and nystagmus can be induced when the horizontally extended arm of a stationary subject is passively rotated about a vertical axis in the shoulder joint.Lateral nystagmus with the fast phase beating in the opposite direction to the arm movement was found consistently; the mean slow phase velocity increased with increasing actual arm velocity and reached about 15 °/sec; the mean position of the eyes was deviated towards the fast phase as in optokinetic nystagmus, and the nystagmus continued after the cessation of stimulation (arthrokinetic after-nystagmus).The existence of an arthrokinetic circularvection and nystagmus indicates a convergence of vestibular and somatosensory afferents from joint receptors. It is concluded that information about joint movements plays an important role within the multisensory processes of self-motion perception.

The Aubert-Fleischl phenomenon: A temporal frequency effect on perceived velocity in afferent motion perception

SummaryApparent velocities of moving visual stimuli are known to be different depending on whether the subject pursues the stimulus (efferently controlled motion perception) or whether the eye is stationary and the image moves across the retina (afferent motion perception). Afferent motion perception of a periodic pattern or a moving single object causes overestimation of velocity (magnitude estimations) as compared to smooth pursuit. This socalled Aubert-Fleischl phenomenon is shown to depend on local temporal frequency stimulation on the retina caused by the repetitive passage of contrast borders of the moving periodic pattern. This is evidenced by the fact that for a given stimulus speed the amount of overestimation is a function of the spatial frequency of the pattern (or the angular subtend of a single moving object) and that the Aubert-Fleischl phenomenon is not observed if a single edge moves. Background characteristics seem not to influence the apparent velocity during smooth pursuit.

Perceived distance and the perceived speed of self-motion: Linear vs. angular velocity?

Experiments are reported in which it was found that, with the angular speed of a visual surround held constant, the perceived speed of rotary self-motion increased linearly with increasing perceived distance of this surround. This finding was in agreement with a motion constancy equation derived from a consideration of object-referred motion perception. Since information concerning distance is necessary for the perception of linear but not angular speed, this finding supports the conclusion that visually perceived rotary self-motion perception is dependent upon perceived linear surround motion at least in the horizontal plane. The visual motion constancy mechanism which operates for object-referred motion can apparently not be switched off for the special case of self-motion perception.

[Visually induced pseudocoriolis-effects and circularvection. A contribution to opto-vestibular interaction].

SummaryCircular vection and Coriolis effects were investigated with combined as well as with separate optokinetic and vestibular rotational stimuli using a rotary chair located inside a cylindrical rotatable drum.Coriolis effects which were elicited by tilting of the head were measured by means of the magnitude estimation technique. Bye movements, ECG, and respiration rate were simultaneously recorded. Results1.Chair and drum rotation could not be distinguished subjectively. In both cases the experience of self-rotation (circular vection) predominated. Furthermore additional stationary acoustical stimuli were integrated into this experience.2.Tilting of the head during pure optokinetic stimulation (rotation of the drum) produced a Pseudocoriolis effect which could not be qualitatively distinguished from the Coriolis effect produced by pure vestibular stimulation (rotation of the chair).3.Optical-optomotor movement control (with the eyes open) inhibited the Coriolis effect produced by vestibular stimuli. This inhibition was directionally specific.4.The visual Pseudocoriolis effect as well as the visually induced inhibition of vestibular afference outlasted the visual stimulus by up to 30 sec. 5. The strongest Coriolis-effects occurred when visual and vestibular movement information did not match.The results are discussed in terms of their significance for visual-vestibular integration in movement perception.ZusammenfassungCircularvektion und Coriolis-Phänomene wurden mit kombinierten und isolierten optokinetischen und vestibulären Drehreizen untersucht. Diese wurden durch einen Drehstuhl und eine konzentrisch dazu angeordnete zylindrische Drehtrommel dargeboten.Die durch Kopfneigung ausgelösten Coriolis-Effekte wurden durch Größenskalierung (magnitude estimation) bestimmt und Augenbewegungen, EKG sowie Atmung simultan registriert. Ergebnisse1.Stuhl- und Trommelrotation können subjektiv nicht unterschieden werden. In beiden Fällen tritt dominant eine Eigendrehempfindung (Circularvektion) auf. Zusätzliche ortsstabile akustische Reize werden in die Eigendrehempfindung integriert.2.Durch Kopfneigungen bei rein optokinetischem Reiz (Trommelrotation) werden Pseudocoriolis-Effekte ausgelöst, die qualitativ nicht von den vestibulären Coriolis-Effekten unterschieden werden können.3.Die optisch-optomotorische Bewegungskontrolle (bei offenen Augen) hemmt die vestibulär ausgelösten Coriolis-Effekte richtungsspezifisch.4.Optische Pseudocoriolis-Effekte und die Hemmung der visuellen auf die vestibuläre Afferenz sind bis zu 30 sec nach Ende des optischen Reizes nachweisbar. 5. Die stärksten Coriolis-Effekte treten bei Richtungsinkongruenz optischer und vestibulärer Bewegungsinformationen auf.Die Ergebnisse werden für die optisch-vestibuläre Integration bei Bewegungswahrnehmung und Schwindel diskutiert.

Visuelle Prävention der Bewegungskrankheit im Auto

SummaryThe differential effects of vision on motion sickness in cars were tested under real road conditions using linear accelerations, in order to confirm earlier laboratory results on visual modulation of vestibular nausea induced by angular accelerations of the body.The 18 voluntary subjects were exposed to repetitive braking maneuvers (linear accelerations: 0.1–1.2 g) on a highway. The simultaneous visual stimulus conditions for the 3 separate days were: I) eyes open, visual control of car motion; II) eyes closed; III) eyes open, artificial stationary visual field (reading).The severity of motion sickness (magnitude estimation 1–10) was a function of the visual stimulus condition with significant differences among these conditions: I) moderate nausea (<1) with adequate visual motion perception; II) medium nausea (≈2) with eyes closed and somatosensory-vestibular excitation only; III) strong nausea (>5) with conflicting sensory input, when vestibular acceleration is in disagreement with the visual information of no movement. Providing ample peripheral vision of the relatively moving surround is the best strategy to alleviate car sickness.ZusammenfassungMit Hilfe von Autoversuchen wurde die früher im Labor für Winkelbeschleunigungen gefundene visuelle Modulation vestibulären Schwindels auf ihre praktische Bedeutung zur physikalischen Prävention von Bewegungskrankheit, vorwiegend durch Linearbeschleunigungen auf der Straße, überprüft.Achtzehn freiwillige Versuchspersonen wurden an drei nicht aufeinanderfolgenden Tagen als Beifahrer in einem Kraftfahrzeug auf einer geraden Autobahn-Teststrecke über 4 × 1,7 km einem festgelegten Muster richtungswechselnder Linearbeschleunigungen (0,1–1,2 g) unter Variation der gleichzeitigen visuellen Reizbedingungen ausgesetzt: I) Augen auf, visuelle Kontrolle der Fahrzeugbeschleunigungen; II) Augen zu; III) Augen auf, künstlicher stationärer Ganzfeldreiz (Kartenlesen).Die Stärke der durch die alternierenden Beschleunigungen ausgelösten Bewegungskrankheit (magnitude estimation 1–10) wurde signifikant durch simultane visuelle Reizbedingungen bestimmt: a) geringe Übelkeit (<1) unter adäquater visueller Bewegungswahrnehmung; b) mittlere Übelkeit (≈2) bei rein vestibulärer Reizung und geschlossenen Augen; c) starke Übelkeit (>5), wenn die visuelle Information scheinbarer Unbewegtheit den labyrinthären Beschleunigungsreizen widerspricht. Bewegungskrankheit in Autos entsteht vorwiegend durch visuell-vestibuläre Reizkonflikte und läßt sich wirkungsvoll durch visuelle Kontrolle der auftretenden Fahrzeugbeschleunigungen unterdrücken.

The European vestibular experiments in spacelab-1

A series of experiments were performed in the Spacelab-1 mission on November/December, 1983, pre-, in-, and postflight. These experiments covered various aspects of the functions of the vestibular system, the inflight tests comprising threshold measurements for linear movements in three orthogonal axes, optokinetic stimulation, vestibulo-ocular reflexes under linear and angular accelerations, caloric stimulation with and without linear accelerations; pre- and postflight tests repeated the inflight protocol with the addition of subjective vertical and eye counter-rotation measurements using a tilt table. One of the most surprising and significant results was the caloric test: strong caloric nystagmus on the two subjects tested was recorded inflight; this was contrary to what was expected from Baranys convection hypothesis for caloric nystagmus.

Spatial frequency effect on the pulfrich stereophenomenon

Abstract The results of two experiments are reported. In the first it was found that the magnitude of the Pulfrich phenomenon is dependent upon the spatial frequency of the moving stimulus pattern: the greater the spatial frequency for a constant filter density and angular speed, the greater the apparent displacement in depth. In the second study, the magnitude of the Pulfrich effect was found to decrease with increasing angular width of moving single stripes up to an angular width of 27°. The data were interpreted as consistent with the view that for the Pulfrich effect the retinal disparity between the moving stimulus and the fixated stationary stimulus is not given by the retinal points actually stimulated at any instant in time, but rather by the registered rate of motion of the stimulus.