The effect of visual-vestibular conflict on the latency of steady-state visually induced subjective rotation

Two experiments were carried out to test the hypothesis that the long onset latency of steady-state subjective rotation induced by rotating a tall striped drum around a stationary observer is the result of visual-vestibular conflict. A reduction of this conflict should, therefore, reduce the length of the latency period. In Experiment 1, visual-vestibular conflict was reduced by providing the observers with corroborating vestibular stimulation at the start of optokinetic stimulation. Onset latencies were found to be significantly shortened with corroborating vestibular stimulation, but to be unaffected by noncorroborating vestibular stimulation. In Experiment 2, testing was done on a group of patients with unilateral (right labyrinth) Ménière’s disease, which produces decreased vestibular sensitivity to rightward body rotation and increased vestibular sensitivity to leftward body rotation. Visual-vestibular conflict during subjective rotation to the right should therefore be decreased, while during leftward subjective rotation it should be increased. The prediction that the latency to steady-state subjective rotation should be shorter than normal with subjective rotation to the left was supported.     

A visually induced illusion of body tilt in a horizontal plane

Unexpected spontaneous reports of an illusion of body orientation have been observed in previous studies on the effects of a tilted overhead frame on supine observers. The present studies were designed in an attempt to describe and measure this illusion. The findings suggest that when objectively aligned with invisible side walls of the room, some subjects may experience an illusion that they are tilted in a horizontal plane with respect to the room walls in the direction opposite to frame tilt from the longitudinal body axes. The results are discussed in terms of a model of visual-vestibular interactions.     

Effect of field size, head motion, and rotational velocity on roll vection and illusory self-tilt in a tumbling room

The effect of field size, velocity, and visual fixation upon the perception of self-body rotation and tilt was examined in a rotating furnished room. Subjects sat in a stationary chair in the furnished room which could be rotated about the body roll axis. For full-field conditions, complete 360 degrees body rotation (tumbling) was the most common sensation (felt by 80% of subjects). Constant tilt or partial tumbling (less than 360 degrees rotation) occurred more frequently with a small field of view (20 deg). The number of subjects who experienced complete tumbling increased with increases in field of view and room velocity (for velocities between 15 and 30 degrees s-1). The speed of perceived self-rotation relative to room rotation also increased with increasing field of view.     

Unstable coupling of body sway with imposed motion precedes visually induced motion sickness

Motion sickness is preceded by differences in the quantitative kinematics of body sway between individuals who (later) become sick and those who do not. In existing research, this effect has been demonstrated only in measures of body sway, relative to the earth. However, body sway can become coupled with imposed oscillatory motion of the illuminated environment, and the nature of this coupling may differ between individuals who become sick and those who do not. We asked whether body sway would become coupled to complex oscillations of the illuminated environment, and whether individual differences in such coupling might be precursors of motion sickness. Standing participants (women) were exposed to complex oscillation of the illuminated environment. We examined the strength of coupling as a function of time during exposure. Following exposure, some participants reported motion sickness. The nature and temporal evolution of coupling differed between participants who later reported motion sickness and those who did not. Our results show that people can couple the complex dynamics of body sway with complex imposed motion, and that differences in the nature of this coupling are related to the risk of motion sickness.     

Influence of head orientation on visually and memory-guided arm movements

In the absence of visual supervision, tilting the head sideways gives rise to deviations in spatially defined arm movements. The purpose of this study was to determine whether these deviations are restricted to situations with impoverished visual information. Two experiments were conducted in which participants were positioned supine and reproduced with their unseen index finger a 2 dimensional figure either under visual supervision or from memory (eyes closed). In the former condition, the figure remained visible (using a mirror). In the latter condition, the figure was first observed and then reproduced from memory. Participants' head was either aligned with the trunk or tilted 30° towards the left or right shoulder. In experiment 1, participants observed first the figure with the head straight and then reproduced it with the head either aligned or tilted sideways. In Experiment 2, participants observed the figure with the head in the position in which the figure was later reproduced. Results of Experiment 1 and 2 showed deviations of the motor reproduction in the direction opposite to the head in both the memory and visually-guided conditions. However, the deviations decreased significantly under visual supervision when the head was tilted left. In Experiment 1, the perceptual visual bias induced by head tilt was evaluated. Participants were required to align the figure parallel to their median trunk axis. Results revealed that the figure was perceived as parallel with the trunk when it was actually tilted in the direction of the head. Perceptual and motor responses did not correlate. Therefore, as long as visual feedback of the arm is prevented, an internal bias, likely originating from head/trunk representation, alters hand-motor production irrespectively of whether visual feedback of the figure is available or not.     

Influence of coactors on performance of visually impaired runners

The purpose of this exploratory study was to determine the influence of coactors on the running performance of 13 visually impaired individuals. There was no significant difference for visually impaired sprint runners running alone and with a coactor. The "mere presence" of a coactor was not enough for social facilitation to occur when visual evaluation was not present.     

Depth separation between foreground and background on visually induced perception of self-motion

A uniformly moving visual pattern can induce observer's self-motion perception in the opposite direction (vection), and an additional static stimulus can modulate (facilitate or inhibit) the strength of it. The present study was designed to investigate the effects of stimulus depth order and the depth distances of the visual stimulus on the inhibition and facilitation of vection caused by the additional static stimulus, measuring duration and estimated magnitude of vection as indices of vection strength. Analysis of this psychophysical experiment with four participants indicated that the static foreground presented in front of the moving pattern can facilitate vection, whereas the static background inhibits it (Duration: F1,3= 12.06, p<.05; Estimation: F1,3= 13.87, p<.05). Furthermore, the depth distances from the observer or the depth separation between the foreground and the background did not affect the self-motion perception (F2,6 < 1.0 for duration and estimation).     

The effect of meaning on the allocation of visually induced movement

The directional characteristics of a meaningful target were found to affect its apparent motion when it was displaced relative to a neutral object. The effect was destroyed, however, when the target was surrounded by a frame. This was because the frame imparted a meaning which tended to override that conveyed by the target.     

Influence of visually induced expectation on perceived motor effort: A visual-proprioceptive interaction at the Santa Cruz Mystery Spot

It is known that dense objects seem heavier than larger, less dense objects of the same weight. We have investigated a related illusion, in which visual context biases the apparent weight of a single object. The apparatus is a cabin on a steep hillside near Santa Cruz, CA, tilted 17° from vertical. From its ceiling hangs a weight on a chain. The cabin’s tilt makes the weight appear suspended at an angle. Pushing the weight toward the visually based vertical is perceived as difficult, whereas pushing it away from the visual vertical is perceived as easy. Seven subjects pushed the weight in both directions, judging required effort on a double-anchored 1–10 scale. All experienced the effort illusion, with no significant subject effect. When subjects’ eyes were closed, the effect was smaller but still present. Apparently proprioceptive and skin inputs, equal for both directions, are ignored or underweighted as visually based expectations influence perceived effort.     

Perception of self-tilt in a true and illusory vertical plane

A tilted furnished room can induce strong visual reorientation illusions in stationary subjects. Supine subjects may perceive themselves upright when the room is tilted 90 degrees so that the visual polarity axis is kept aligned with the subject. This 'upright illusion' was used to induce roll tilt in a truly horizontal, but perceptually vertical, plane. A semistatic tilt profile was applied, in which the tilt angle gradually changed from 0 degrees to 90 degrees, and vice versa. This method produced larger illusory self-tilt than usually found with static tilt of a visual scene. Ten subjects indicated self-tilt by setting a tactile rod to perceived vertical. Six of them experienced the upright illusion and indicated illusory self-tilt with an average gain of about 0.5. This value is smaller than with true self-tilt (0.8), but comparable to the gain of visually induced self-tilt in erect subjects. Apparently, the contribution of nonvisual cues to gravity was independent of the subject's orientation to gravity itself. It therefore seems that the gain of visually induced self-tilt is smaller because of lacking, rather than conflicting, nonvisual cues. A vector analysis is used to discuss the results in terms of relative sensory weightings.     

Effects of supine body position and low radial accelerations on the visually perceived apparent zenith

The visually perceived eye level (VPEL) has been shown to shift toward the lower part of the body in upright subjects facing toward the axis of rotation on a centrifuge. This shift occurs in the same direction as the shift in the gravito-inertial forces (Gis) produced by very low radial acceleration (centrifugation) combined with gravity. The purpose of this study was to determine whether the same phenomenon affects the visually perceived apparent zenith (VPAZ) in subjects in a supine position. Twelve supine subjects were instructed to set a luminous target to the VPAZ, either while they were in total darkness and motionless or while undergoing very low centrifugation. Data showed that Gis induced a VPAZ shift similar to that observed for the VPEL. Thus, as is the case for the VPEL, the corresponding logarithmic psychophysical function of the VPAZ may be considered to be a type of oculogravic illusion phenomenon with differences in the subjects' that differs from subject to subject, depending on the subject's sensitivity to low radial accelerations. Data on VPEL and VPAZ support the notion that the subjective perception of eye level in total darkness takes into account changes--even if extremely slight-in the direction of the gravito-inertial forces produced by the combination of gravity and low radial accelerations, although subjects are unaware of the Gi shift. However, depending on the intensity of the radial acceleration and the angular deviation of Gi relative to G, the shift of the VPEL and the VPAZ can be either amplified or attenuated. Moreover, differences between VPEL and VPAZ responses suggest two explanatory assumptions--namely, that this is (1) a peripheral phenomenon dependent on the neurophysiological anisotropy of the otolithic system or (2) a central phenomenon dependent on the relevance assigned to the peripheral information by the integrative sensory functions and the associative processes.     

Coherent modulation of stimulus colour can affect visually induced self-motion perception

The effects of dynamic colour modulation on vection were investigated to examine whether perceived variation of illumination affects self-motion perception. Participants observed expanding optic flow which simulated their forward self-motion. Onset latency, accumulated duration, and estimated magnitude of the self-motion were measured as indices of vection strength. Colour of the dots in the visual stimulus was modulated between white and red (experiment 1), white and grey (experiment 2), and grey and red (experiment 3). The results indicated that coherent colour oscillation in the visual stimulus significantly suppressed the strength of vection, whereas incoherent or static colour modulation did not affect vection. There was no effect of the types of the colour modulation; both achromatic and chromatic modulations turned out to be effective in inhibiting self-motion perception. Moreover, in a situation where the simulated direction of a spotlight was manipulated dynamically, vection strength was also suppressed (experiment 4). These results suggest that observer's perception of illumination is critical for self-motion perception, and rapid variation of perceived illumination would impair the reliabilities of visual information in determining self-motion.     

The role of eye movements in the perception of visually induced motion

Changes in eye position were recorded while S experienced visually induced motion. Movement of the eye was not found to correlate, in either direction or extent, with this type of apparent motion. Induced movement was explained, therefore, in terms of a change in phenomenal rather than retinal location.     

The role of eye movements in the perception of visually induced autokinesis

Changes in eye position were recorded physiologically while S experienced visually induced autokinesis. Eye movements did not seem to sufficiently explain this phenomenon. Apparent motion was found to be based upon a change in phenomenal rather than retinal location. Special consideration was given to those parameters possibly responsible for paradoxical motion.     

Relationships between catastrophic cognitions and body sensations in anxiety disordered, mixed diagnosis, and normal subjects

Clark's (Behaviour Research and Therapy, 24, 461-470, 1986) cognitive model proposes that panic attacks result from the catastrophic misinterpretation of certain body sensations. The present study examined correlations between feared body sensations and catastrophic cognitions. It was hypothesized that regardless of diagnostic status meaningful correlations between sensations and cognitions would be obtained. Three groups--anxiety disordered patients (n = 33), nonanxiety disordered patients (n = 57), and normals (n = 60)--completed the Agoraphobic Cognitions Questionnaire and the Body Sensations Questionnaire. Results generally supported the hypothesis and the cognitive model of panic and anxiety. Limitations of the correlational methodology are discussed, and treatment implications are noted.     

Anatomically plausible illusory posture affects mental rotation of body parts

During mental rotation (MR) of body parts, people internally simulate the movement of their corresponding body segments. These sensory–motor mechanisms render MR sensitive to proprioceptive information (e.g., posture). Similar mechanisms can alter illusory hand ownership following synchronous visuotactile stimulation (e.g., the rubber hand illusion [RHI]). In the present study, we first showed that illusory ownership for a fake hand can also be induced when the posture of the fake hand (palm-up) does not correspond with the subject’s physical hand posture (palm-down). Then we tested whether illusory ownership for a fake hand in such a posture impacts the MR of hands carried out immediately and repeatedly after the RHI. The results showed that MR was altered for the view corresponding to the fake hand’s posture, but not for other views. Additionally, these effects depended on illusory ownership, as only synchronous visuotactile stimulation was found to lead to these changes, characterized by a modulation of the rotation-dependent profile of MR response times. These findings show that similar sensory–motor mechanisms are recruited during the MR of hands and illusory hand ownership manipulated through multisensory mismatch, and that bottom-up visuotactile stimulation interferes with high-level imagery processes.     

Covariation of sex differences in mental rotation with body size

Sex difference in mental rotation ability was reconsidered. The Vandenberg-Kuse figures were administered to 120 male and 76 female students from the Medical School of BlackSea Technical University in Trabzon, Turkey to assess the mental rotation ability. Students' height and weight were measured. As expected, men outperformed women on this test and had greater height and weight. Number correct on mental rotation test significantly correlated with height and weight for the total sample and for men, but only with weight for women. Using weight as covariate, the sex difference was no longer significant. The mean mental rotation score was significantly higher for heavy women than for light men. There was a positive correlation between weight and mental rotation test scores for heavy women, but height and weight were negatively correlated with mental rotation test scores for light men. These results suggest that there is no sex difference in mental rotation ability as measured.