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).     

Chromaticity, spatial complexity, and self-motion perception

The effects of visual field color and spatial complexity on self-motion perception were investigated by placing observers inside a large rotating cylinder (optokinetic drum). Under optokinetic-drum conditions visually induced self-motion (vection) is typically perceived within 30 s, even though all forms of sensory input (eg vestibular, proprioceptive, auditory), except vision, indicate that the observer is stationary. It was hypothesized that vection would be hastened and vection magnitude increased by adding chromatic colors and spatial complexity to the lining of an optokinetic drum. Addition of these visual-field characteristics results in an array that shares more visual-field characteristics with our typical environment that usually serves as a stable frame of reference regarding self-motion perception. In the color experiment, participants viewed vertical stripes that were: (i) black and white, (ii) various gray shades, or (iii) chromatic. In the spatial complexity experiment, participants were presented with: (i) black-and-white vertical stripes, or (ii) a black-and-white checkerboard pattern. Drum rotation velocity was 5 rev. min(-1) (30 degrees s(-1)), and both vection onset and magnitude were measured for 60 s trials. Results indicate that chromaticity and spatial complexity hasten the onset of vection and increase its perceived magnitude. Chromaticity and spatial complexity are common characteristics of the environments in which our visual system evolved. The presence of these visual-field features in an optic flow pattern may be treated as an indicator that the scene being viewed is stationary and that the observer is moving.     

Linear vection in the central visual field facilitated by kinetic depth cues.

Illusory self-motion (vection) is thought to be determined by motion in the peripheral visual field, whereas stimulation of more central retinal areas results in object-motion perception. Recent data suggest that vection can be produced by stimulation of the central visual field provided it is configured as a more distant surface. In this study vection strength (tracking speed, onset latency, and the percentage of trials where vection was experienced) and the direction of self-motion produced by displays moving in the central visual field were investigated. Apparent depth, introduced by using kinetic occlusion information, influenced vection strength. Central displays perceived to be in the background elicited stronger vection than identical displays appearing in the foreground. Further, increasing the eccentricity of these displays from the central retina diminished vection strength. If the central and peripheral displays were moved in opposite directions, vection strength was unaffected, and the direction of vection was determined by motion of the central display on almost half of the trials when the centre was far. Near centres produced fewer centre-consistent responses. A complete understanding of linear vection requires that factors such as display size, retinal locus, and apparent depth plane are considered.     

Type of motion in inverted self-motion perception induced by a foreground stimulus

Slowly moving foreground induces an illusory self-motion perception in the same direction as its motion direction (inverted vection). In this study, the effects of motion type of the foreground stimulus on inverted vection were investigated using a sample of 3 men and 1 woman. As indices of perceived strength of the inverted vection, duration and estimated magnitude were measured. Analysis of the psychophysical experiment indicated that a translating foreground induced inverted linear vection in the same direction as the stimulus motion. However, a rotating foreground did not induce an inverted roll vection. Statistical analyses indicate that there is a significant difference between two foreground motion conditions (Duration: t3=14.54, p <.01; Estimation: t3=16.92, p<.01). This result supports the hypothesis that eye-movement information is responsible for the occurrence of inverted vection.     

The perception of self-motion induced by central and peripheral visual stimuli moving in opposite directions

The effects of the size of a stimulus and its eccentricity (central or peripheral) on the visually induced perception of horizontal translational self-motion (vection) were investigated. The central and peripheral areas of the observers' visual field were simultaneously stimulated by random dot patterns that moved in opposite directions. The results of two experiments indicated that the effects of central and peripheral presentations of the moving visual pattern are equivalent, and that vection strength is determined by the stimulus size and speed but not by its eccentricity. These results are consistent with the findings of previous studies that suggested that there are no qualitative differences in the vection-inducing potentials of the central and peripheral areas of the visual field, and are counter to the more traditional hypothesis, which has assumed that the perception of self-motion is specifically assigned to peripheral vision.     

Critical role of foreground stimuli in perceiving visually induced self-motion (vection)

The effects of a foreground stimulus on vection (illusory perception of self-motion induced by a moving background stimulus) were examined in two experiments. The experiments reveal that the presentation of a foreground pattern with a moving background stimulus may affect vection. The foreground stimulus facilitated vection strength when it remained stationary or moved slowly in the opposite direction to that of the background stimulus. On the other hand, there was a strong inhibition of vection when the foreground stimulus moved slowly with, or quickly against, the background. These results suggest that foreground stimuli, as well as background stimuli, play an important role in perceiving self-motion.     

Attentional modulation of self-motion perception

Attentional effects on self-motion perception (vection) were examined by using a large display in which vertical stripes containing upward or downward moving dots were interleaved to balance the total motion energy for the two directions. The dots moving in the same direction had the same colour, and subjects were asked to attend to one of the two colours. Vection was perceived in the direction opposite to that of non-attended motion. This indicates that non-attended visual motion dominates vection. The attentional effect was then compared with effects of relative depth. Clear attentional effects were again found when there was no relative depth between dots moving in opposite directions, but the effect of depth was much stronger for stimuli with a relative depth. Vection was mainly determined by motion in the far depth plane, although some attentional effects were evident even in this case. These results indicate that attentional modulation for vection exists, but that it is overridden when there is a relative depth between the two motion components.     

Inhibition of vection by red

We investigated the effects of colors on vection induction. Expanding optical flows during one’s forward self-motion were simulated by moving dots. The dots and the background were painted in equiluminant red and green. Experiments 1 and 2 showed that vection was weaker when the background was red than when the background was green. In addition, Experiment 3 showed that vection was weaker when the moving dots were red than when the dots were green. Experiment 4 demonstrated that red dots on a red background induced very weak vection, as compared with green dots on a green background. In Experiments 5 and 6, we showed that the present results could not be explained by a luminance artifact. Furthermore, Experiment 7 showed that a moving red grating induced weaker vection than did a green one. We concluded that a red visual stimulus inhibits vection.     

Jitter and size effects on vection are immune to experimental instructions and demands

Both coherent perspective jitter and explicit changing-size cues have been shown to improve the vection induced by radially expanding optic flow. We examined whether these stimulus-based vection advantages could be modified by altering cognitions and/or expectations about both the likelihood of self-motion perception and the purpose of the experiment. In the main experiment, participants were randomly assigned into two groups-one where the cognitive conditions biased participants towards self-motion perception and another where the cognitive conditions biased them towards object-motion perception. Contrary to earlier findings by Lepecq et al (1995 Perception 24 435-449), we found that identical visual displays were less likely to induce vection in 'object-motion-bias' conditions than in 'self-motion bias' conditions. However, significant jitter and size advantages for vection were still found in both cognitive conditions (cognitive bias effects were greatest for non-jittering same-size control displays). The current results suggest that if a sufficiently large vection advantage can be produced when participants are expecting to experience self-motion, it is likely to persist in object-motion-bias conditions.     

Induction and impairment of saturated yaw and surge vection

A flight simulator was used to investigate the perception of self-motion and visual scene motion during the induction of saturated 10 deg/sec yaw and 50 m/sec surge vection, and during subsequent impairment of saturated vection by inertial motions. The subjects (n = 5) did not perceive any self-acceleration or visual scene deceleration during the induction of saturated vection but perceived a rather sudden change in self-velocity and visual scene velocity. The mean group times to saturated vection were 3.0 sec for yaw and 2.7 sec for surge. Above certain inertial motion amplitudes, the subjects reported additional self-motion from the applied inertial motions while experiencing saturated vection. To impair saturated yaw vection, these amplitudes were 0.6 m/sec2, 0.4 m/sec2, 8 deg/sec2, and 5 deg/sec2, for surge, sway, roll and yaw motions, respectively. To impair saturated surge vection, these amplitudes were 0.6 m/sec2, 0.3 m/sec2, 5 deg/sec2, and 4 deg/sec2, respectively. The results indicate that saturated vection is more robust for translations than for rotations because the rotational inertial amplitudes were closer to the amplitudes at which the applied inertial motion was perceived than the translational inertial amplitudes.     

Inertial acceleration as a measure of linear vection: An alternative to magnitude estimation

The present study focused on the development of a procedure to assess perceived self-motion induced by visual surround motion—vection. Using an apparatus that permitted independent control of visual and inertial stimuli, prone observers were translated along their headx-axis (fore/aft). The observers’ task was to report the direction of self-motion during passive forward and backward translations of their bodies coupled with exposure to various visual surround conditions. The proportion of “forward” responses was used to calculate each observer’s point of subjective equality (PSE) for each surround condition. The results showed that the moving visual stimulus produced a significant shift in the PSE when data from the moving surround condition were compared with the stationary surround and no-vision condition. Further, the results indicated that vection increased monotonically with surround velocities between 4 and 40°/sec. It was concluded that linear vection can be measured in terms of changes in the amplitude of whole-body inertial acceleration required to elicit equivalent numbers of “forward” and “backward” self-motion reports.     

Stimulus eccentricity and spatial frequency interact to determine circular vection.

While early research suggested that peripheral vision dominates the perception of self-motion, subsequent studies found little or no effect of stimulus eccentricity. In contradiction to these broad notions of 'peripheral dominance' and 'eccentricity independence', the present experiments showed that the spatial frequency of optic flow interacts with its eccentricity to determine circular vection magnitude--central stimulation producing the most compelling vection for high-spatial-frequency stimuli and peripheral stimulation producing the most compelling vection for lower-spatial-frequency stimuli. This interaction appeared to be due, in part at least, to the effect that the higher-spatial-frequency moving pattern had on subjects' ability to organise optic flow into related motion about a single axis. For example, far-peripheral exposure to this high-spatial-frequency pattern caused many subjects to organise the optic flow into independent local regions of motion (a situation which clearly favoured the perception of object motion not self-motion). It is concluded that both high-spatial-frequency and low-spatial-frequency mechanisms are involved in the visual perception of self-motion--with their activities depending on the nature and eccentricity of the motion stimulation.     

Effects of stimulus eccentricity on vection reevaluated with a binocularly defined depth1

Abstract: The effects of stimulus eccentricity (central or peripheral) on vection (visually induced self‐motion perception) were investigated using a stimulus combination consisting of a static foreground and a moving background, the depths of which were defined by binocular disparity. By using these stimulus settings, the effect of stimulus eccentricity can be assessed without any artifacts in the perceived depth of the stimulus, which would covary with the stimulus eccentricity. The results of this psychophysical experiment indicated that stimulus eccentricity cannot affect the strength of vection, and that both the central and peripheral stimuli can induce self‐motion perception with equal magnitudes if the stimulus sizes are equalized. The present investigation, which used a controlled stimulus depth condition, clearly negated the idea of the peripheral dominance of vection, which has been accepted for a long time.     

Cyclopean stimulation can influence sensations of self-motion in normal and stereoblind subjects

Subjects experienced an illusion of self-motion when viewing the randomly patterned inner surface of a cylinder rotating about their main body axis. This sensation of rotation in a direction opposite to the direction of cylinder rotation is known as circular vection. An experiment was conducted to ascertain if the production of circular vection involved a binocular process in the visual system. Using dichoptic strobe illumination, stimuli were created that were identical monocularly but different binocularly. Groups of normal and stereoblind subjects were tested. The presence of purely binocular (cyclopean) stimulation increased the reported magnitude of vection for both groups. We conclude that a binocular process is involved in the production of circular vection and that this process retains its binocularity in stereoblind subjects.     

Spatiotemporal boundaries of linear vection

Thresholds for the perception of linear vection were measured. These thresholds allowed us to define the spatiotemporal contrast surface sensitivity and the spatiotemporal domain of the perception of rectilinear vection (a visually induced self-motion in a straight line). Moreover, a Weber’s law was found, such that a mean relative differential threshold in angular velocity of about 41% is necessary to perceive curvilinear vection. This visually induced self-motion corresponds to the sensation of moving in a curved path. It is proposed that curvilinear vection is induced when the apparent velocity difference is detectable. The spatiotemporal domain of perception of rectilinear vection and its spatiotemporal contrast surface sensitivity are centered on low spatial frequencies. Concurrently, the values which correspond to the relative differential thresholds of curvilinear vection are low spatial frequencies. Accordingly, the peripheral ambient visual system seems to be involved in perceiving linear vection. It is argued further that the central ambient system might also be involved in the processing of linear vection.     

Inconsistent locomotion inhibits vection

We measured the strength of illusory self-motion perception (vection) with and without locomotion on a treadmill. The results revealed that vection was inhibited by inconsistent locomotion, but facilitated by consistent locomotion.     

Properties of curvilinear vection

Approximately linear relationships were observed between contrast, spatial frequency, temporal frequency, or velocity of stimulation and perceived velocity of curvilinear vection&#x2014;that is, a visually induced self-motion in a curved path. Similarly, linear relationships were also found between the perceived degree of curvature of curvilinear vection and spatial frequency or velocity of stimulation. Since the perceived velocity of curvilinear vection varies with contrast, spatial frequency, temporal frequency, and angular velocity, and the perceived degree of curvature of curvilinear vection varies only with spatial frequency and angular velocity, peripheral vision is not sufficient for computing accurately the curvilinear component of induced self-motion in a curved path. Concurrently, it was shown that the perceived direction of curvilinear vection is not always unambiguously perceived (Sauvan & Bonnet, 1989). Consequently, it is suggested that two different types of visual processing, which involve the peripheral or the central vision, underlie the processing of curvilinear vection.     

Effect of stationary objects on illusory forward self-motion induced by a looming display

It has previously been shown that when a moving and a stationary display are superimposed, illusory self-rotation (circular vection) is induced only when the moving display appears as the background. Three experiments are reported on the extent to which illusory forward self-motion (forward vection) induced by a looming display is inhibited by a superimposed stationary display as a function of the size and location of the stationary display and of the depth between the stationary and looming displays. Results showed that forward vection was controlled by the display that was perceived as the background, and background stationary displays suppressed forward vection by about the same amount whatever their size and eccentricity. Also, the perception of foreground-background properties of competing displays determined which controlled forward vection, and this control was not tied to specific depth cues. The inhibitory effect of a stationary background on forward vection was, however, weaker than that found with circular vection. This difference makes sense because, for forward body motion, the image of a distant scene is virtually stationary whereas, when the body rotates, it is not.     

Accelerating self-motion displays produce more compelling vection in depth

We examined the vection in depth induced when simulated random self-accelerations (jitter) and periodic self-accelerations (oscillation) were added to radial expanding optic flow (simulating constant-velocity forward self-motion). Contrary to the predictions of sensory-conflict theory frontal-plane jitter and oscillation were both found to significantly decrease the onsets and increase the speeds of vection in depth. Depth jitter and oscillation had lesser, but still significant, effects on the speed of vection in depth. A control experiment demonstrated that adding global perspective motion which simulated a constant-velocity frontal-plane self-motion had no significant effect on vection in depth induced by the radial component of the optic flow. These results are incompatible with the notion that constant-velocity displays produce optimal vection. Rather, they indicate that displays simulating self-acceleration can often produce more compelling experiences of self-motion in depth.     

The latency of circular vection during different accelerations of the optokinetic stimulus

Subjects were seated inside a full-field optokinetic cylinder which was accelerated with values between. 1 and 100 deg/sec2. Subjects indicated when motion was first detected. Latency for onset of self-motion shows a minimum of around 5 deg/sec2 and increases for lower and faster accelerations of the visual surround. In the low acceleration range, up to 5 deg/sec2, all movement is perceived as circular vection, that is, self-rotation. With higher accelerations, motion of the visual surround is perceived initially; over seconds, this gradually transforms to circular vection. Velocity estimation during low acceleration is better than during comparable vestibular acceleration. During subject rotation in the light, that is, when both the visual and vestibular inputs combine to generate a velocity signal, detection of motion has the shortest latency and represents actual velocity over a wider range than it does with each stimulus alone.