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.     

Influence of body roll on visually induced sensations of self-tilt and rotation

Illusory self-tilt and illusory self-motion (vection) produced by rotation of a 360 degrees visual scene about the subject's roll axis was measured as a function of the presence or absence of actual rotation of the subject during acceleration of the visual scene. Rotation of the subject to a tilt of 15 degrees was at two levels of acceleration (onset) and with or without a delay between initial rotation and subsequent return (washout) to the vertical position. In one set of conditions, visual motion and subject motion were in opposite directions (concordant) and in another set they were in the same direction (discordant). In two control conditions, the subject was rotated while the visual scene remained stationary. For concordant motion the main effect of body rotation was to reduce the time taken by the subject to indicate self-tilt as compared with the response time to visual motion alone. The magnitude of estimated self-tilt was increased by actual body tilt as could be expected from addition of the perceived actual body tilt and the illusory body tilt induced by visual rotation. This effect of augmented body tilt did not persist after the body was returned to the vertical. The magnitude of vection was not markedly influenced by body rotation and washout. For discordant motion of body and the visual scene, subjects were confused and their responses were very variable, suggesting a nonlinear visual--vestibular interaction.     

The role of visual and nonvisual information in the control of locomotion

During locomotion, retinal flow, gaze angle, and vestibular information can contribute to one's perception of self-motion. Their respective roles were investigated during active steering: Retinal flow and gaze angle were biased by altering the visual information during computer-simulated locomotion, and vestibular information was controlled through use of a motorized chair that rotated the participant around his or her vertical axis. Chair rotation was made appropriate for the steering response of the participant or made inappropriate by rotating a proportion of the veridical amount. Large steering errors resulted from selective manipulation of retinal flow and gaze angle, and the pattern of errors provided strong evidence for an additive model of combination. Vestibular information had little or no effect on steering performance, suggesting that vestibular signals are not integrated with visual information for the control of steering at these speeds.     

Influences of the perception of self-motion on postural parameters.

We examined how spatial and temporal characteristics of the perception of self-motion, generated by constant velocity visual motion, was reflected in orientation of the head and whole body of young adults standing in a CAVE, a virtual environment that presents wide field of view stereo images with context and texture. Center of pressure responses from a force plate and perception of self-motion through orientation of a hand-held wand were recorded. The influence of the perception of self-motion on postural kinematics differed depending upon the plane and complexity of visual motion. Postural behaviors generated through the perception of self-motion appeared to contain a confluence of the cortically integrated visual and vestibular signals and of other somatosensory inputs. This would suggest that spatial representation during motion in the environment is modified by both ascending and descending controls. We infer from these data that motion of the visual surround can be used as a therapeutic tool to influence posture and spatial orientation, particularly in more visually sensitive individuals following central nervous system (CNS) impairment.     

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.     

When Walking Makes Perception Better

ABSTRACT— When we move, the visual world moves toward us. That is, self-motion normally produces visual signals (flow) that tell us about our own motion. But these signals are distorted by our motion: Visual flow actually appears slower while we are moving than it does when we are stationary and our surroundings move past us. Although for many years these kinds of distortions have been interpreted as a suppression of flow to promote the perception of a stable world, current research has shown that these shifts in perceived visual speed may have an important function in measuring our own self-motion. Specifically, by slowing down the apparent rate of visual flow during self-motion, our visual system is able to perceive differences between actual and expected flow more precisely. This is useful in the control of action.     

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.     

Perception of visual speed while moving

During self-motion, the world normally appears stationary. In part, this may be due to reductions in visual motion signals during self-motion. In 8 experiments, the authors used magnitude estimation to characterize changes in visual speed perception as a result of biomechanical self-motion alone (treadmill walking), physical translation alone (passive transport), and both biomechanical self-motion and physical translation together (walking). Their results show that each factor alone produces subtractive reductions in visual speed but that subtraction is greatest with both factors together, approximating the sum of the 2 separately. The similarity of results for biomechanical and passive self-motion support H. B. Barlow's (1990) inhibition theory of sensory correlation as a mechanism for implementing H. Wallach's (1987) compensation for self-motion.     

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.     

Narcissistic people cannot be moved easily by visual stimulation

We examined the relationship between personality and visually induced self-motion perception (latency, duration, and magnitude). A psychological experiment with radially expanding patterns that induced self-motion perception along the fore and aft axis was conducted, followed by personality assessments. We found that all the measures of self-motion perception we examined correlated negatively with the degree of narcissistic traits.     

Balancing awareness: Vestibular signals modulate visual consciousness in the absence of awareness

The processing of visual and vestibular information is crucial for perceiving self-motion. Visual cues, such as optic flow, have been shown to induce and alter vestibular percepts, yet the role of vestibular information in shaping visual awareness remains unclear. Here we investigated if vestibular signals influence the access to awareness of invisible visual signals. Using natural vestibular stimulation (passive yaw rotations) on a vestibular self-motion platform, and optic flow masked through continuous flash suppression (CFS) we tested if congruent visual–vestibular information would break interocular suppression more rapidly than incongruent information. We found that when the unseen optic flow was congruent with the vestibular signals perceptual suppression as quantified with the CFS paradigm was broken more rapidly than when it was incongruent. We argue that vestibular signals impact the formation of visual awareness through enhanced access to awareness for congruent multisensory stimulation.     

Optical flow and viewpoint change modulate the perception and memorization of complex motion

Participants observed a point-light character (PLC) performing a gymnastic movement. They either memorized the final PLC orientation from the initial viewpoint, to match it to a test posture (memory task), or judged whether the biological motion appeared continuous (perceptual task), despite a viewpoint change. The observer could be either static or virtually in motion (pan or track) while looking at the movement from the initial viewpoint. The presence of a spatial layout during virtual self-motion induced a global optical flow specifying the translational component of the PLC movement, rendering the event more predictable for the participants. A representational momentum effect was observed in the memory task, suggesting that when a visual stimulation, such as a PLC motion, is abruptly stopped, its dynamics survive. In contrast, structural and transformational invariants specifying the PLC motion were sufficient to solve the perceptual task accurately. Finally, both the remembering of the final posture and the perception of continuity degraded with an increase in viewpoint change due to tilt/slant posture orientation matching, indicating that orientation processes interfered with event perception.     

Induced self-motion in central vision

Previous research on visually induced self-motion found that stimulation of the central visual field (up to 30 degrees in diameter) results in perceived object motion while self-motion requires peripheral stimulation. In the present study, perceived self-motion was induced with a radially expanding pattern simulating observer motion through a space filled with dots, with visual angles of 7.5 degrees, 10.6 degrees, 15 degrees, and 21.2 degrees. Speed and texture density were also varied. The duration of reported self-motion (a) decreased with increased speed, (b) failed to increase with increased visual angle, and (c) decreased with visual angle at the highest speed level. In a second experiment, subjects rated the perceived depth of the displays. The speed and speed/area interaction effects on judged depth matched those found for induced self-motion. These results suggest an extension of the focal/ambient theory: In addition to a more primitive ambient processing mode that requires peripheral vision, there is a higher level system concerned with ambient processing that functions in the central visual field and uses more complex stimulus information, such as internal depth represented in a radially expanding pattern.     

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.     

To pass or not to pass: More a question of body orientation than visual cues

This study investigated the influence of pitch body tilt on judging the possibility of passing under high obstacles in the presence of an illusory horizontal self-motion. Seated subjects tilted at various body orientations were asked to estimate the possibility of passing under a projected bar (i.e., a parking barrier), while imagining a forward whole-body displacement normal to gravity. This task was performed under two visual conditions, providing either no visual surroundings or a translational horizontal optic flow that stopped just before the barrier appeared. The results showed a main overestimation of the possibility of passing under the bar in both cases and most importantly revealed a strong influence of body orientation despite the visual specification of horizontal self-motion by optic flow (i.e., both visual conditions yielded a comparable body tilt effect). Specifically, the subjective passability was proportionally deviated towards the body tilt by 46% of its magnitude when facing a horizontal optic flow and 43% without visual surroundings. This suggests that the egocentric attraction exerted by body tilt when referring the subjective passability to horizontal self-motion still persists even when anchoring horizontally related visual cues are displayed. These findings are discussed in terms of interaction between spatial references. The link between the reliability of available sensory inputs and the weight attributed to each reference is also addressed.     

Perceiving object motion using vision and touch

In a previous experiment, we showed that bistable visual object motion was partially disambiguated by tactile input. Here, we investigated this effect further by employing a more potent visuotactile stimulus. Monocular viewing of a tangible wire-frame sphere (TS) rotating about its vertical axis produced bistable alternations of direction. Touching the TS biased simultaneous and subsequent visual perception of motion. Both of these biases were in the direction of the tactile stimulation and, therefore, constituted facilitation or priming, as opposed to interference or adaptation. Although touching the TS biased visual perception, tactile stimulation was not able to override the ambiguous visual percept. This led to periods of sensory conflict, during which visual and tactile motion percepts were incongruent. Visual and tactile inputs can sometimes be fused to form a coherent percept of object motion but, when they are in extreme conflict, can also remain independent.     

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.     

自身运动认知的神经机制

通过光流信息来指导个体在环境中有效移动是我们视觉神经系统的一项核心任务。在灵长类的大脑皮层, 视觉运动的信息加工是由位于背侧通路的一系列脑区来完成的, 这一信息通路主要参与运动和空间动作的分析。在高级视皮层, 视觉系统很可能利用非视觉信息来补偿因眼动造成的光流模式扭曲, 以重建对自身运动方向的正确表征。根据目前研究进展, MST和VIP这两个位于顶叶的脑区都参与了自身运动认知过程, 并且对精确的自身运动方向判断是不可或缺的。本文系统介绍了近些年来在自身运动认知神经机制研究领域的进展, 尤其是神经生理学家们利用非人灵长类动物模型在自身运动认知皮层处理机制方面的成果。同时也提出了一些深入研究急需解决的关键问题。     

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.     

A novel automatic procedure for measuring ocular counterrolling: A computeranalytical method to determine the eye’s roll angle while subjects work on perceptual tasks

In investigations of the perception of space, the consideration of ocular counterrolling-the movement of the eye around its visual axis in response to body movement-is crucially important. The angle of this movement must be known in order for one to determine the precise retinal coordinates of a distal object. Following transformation, this stimulus serves as a reliable cue for visual direction. The otolith organs provide information about body tilt and are responsible for ocular counterrolling. A novel, noninvasive method to measure ocular counterrolling, based on the cross-correlation of digitized video pictures of the eyes, is presented. The resolution attained was ≤ 0.1°. The computer analysis is fully automatic and fast, and it can be performed while subjects work on perceptual tasks. No direct access to the eyeballs is required. Data from 4 subjects showing the counterrolling profile in various body positions are presented.