Perception Of Object Motion Research Articles

Torsional eye movements are facilitated during perception of self-motion.

Visual motion in the roll plane elicits torsional optokinetic nystagmus (tOKN) with intermittent periods of illusory, contradirectional self-motion (circularvection, CV). The CV may also have a component of whole-body tilt if the axis of stimulus rotation is not aligned with the direction of gravity. We report how the characteristics of tOKN are affected by the presence of CV. Subjects had their eye movements recorded by VOG whilst viewing a full-field stimulus rotating at 30-60 degrees/s about their naso-occipital axis. They were tested in upright and supine posture and signalled the presence-absence of CV with a pushbutton. In both postures, during CV, tOKN slow-phase gain was found to be enhanced and average torsional eye position shifted in the direction opposite to stimulus rotation. When supine, slow-phase gain was greater than when upright both during the perception of object-motion and during CV. The effects may be explained in terms of a relegation of restraining vestibular input to the torsional oculomotor system during CV and illusory tilt.

The Development of Infants' Perception of Object Movement Along Inclines

Three experiments investigated 10- and 16-month-old infants' perceptions of events involving a computer-generated ball rolling up or down an incline. Experiment 1 demonstrated that infants do not have a priori preferences for either impossible or possible events. In Experiments 2 and 3, infants were habituated to either a possible or an impossible event and then shown three novel events that involved changes in individual features that may or may not correspond to changes in possibility. Ten-month-old infants responded to changes in individual features when habituated to downward movement and did not discriminate among any changes when habituated to upward movement. Sixteen-month-old infants responded to possibility changes that were accompanied by a change in direction when habituated to downward movement, and responded to changes in individual features when habituated to upward movement. These findings are discussed in terms of a framework by which infants first attend to individual features in events and later respond on basis of the combination of those features.

Motion percepts: “Sense specific,” “kinematic,” or . . . ?

In line with my model of object motion perception (Wertheim 1994) and in contradistinction to what Stoffregen (1994) states, Sauvan's data suggest that percepts of motion are not sense specific. It is here argued that percepts of object- or self-motion are neither sense specific nor do they necessarily stem from what Stoffregen calls “kinematic events.” Stoffregen's error is in believing that we can only perceive object- or self-motion relative to other objects, which implies a failure to realise that percepts of absolute object- or self-motion in space (relative to the earth's surface) do exist as well, even when the earth's surface itself is not perceived.

Attentional modulation in perception of visual motion events.

Identical visual targets moving across each other with equal and constant speed can be perceived either to bounce off or to stream through each other. This bistable motion perception has been studied mostly in the context of motion integration. Since the perception of most ambiguous motion is affected by attention, there is the possibility of attentional modulation occurring in this case as well. We investigated whether distraction of attention from the moving targets would alter the relative frequency of each percept. During the observation of the streaming/bouncing motion event in the peripheral visual field, visual attention was disrupted by an abrupt presentation of a visual distractor at various timings and locations (experiment 1; exogenous distraction of attention) or by the demand of an additional discrimination task (experiments 2 and 3; endogenous distraction of attention). Both types of distractions of attention increased the frequency of the bouncing percept and decreased that of the streaming percept. These results suggest that attention may facilitate the perception of object motion as continuing in the same direction as in the past.

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.

Bilateral vestibular failure impairs visual motion perception even with the head still.

Visual motion perception of a single object, moving with a constant angular velocity of 40 min of arc/s in four orthogonal directions, was measured in eight patients with chronic bilateral vestibular failure (BVF) with the head stationary. Perception of object motion was more severely impaired for horizontal than for vertical directions and the impairment was more pronounced in the dominant eye than the nondominant eye. Impaired motion perception in patients with BVF is best explained by a central visual mechanism that suppresses oscillopsia due to the involuntary retinal slip caused by the defective vestibulo-ocular reflex (VOR). This mechanism cannot be switched off with the head stationary (inactive VOR) and thus causes a measurable deficit of motion perception.

Direction-specific impairment of motion perception and spatial orientation in downbeat and upbeat nystagmus in humans

Downbeat and upbeat nystagmus can be classified as central vestibular syndromes in the vertical (pitch) plane of the vestibulo-ocular reflex (VOR) which are defined by ocular motor, perceptual, and postural manifestations. While the ocular motor syndrome was often studied investigations on the perceptual consequences for spatial orientation and motion perception are rare. Subjective visual straight ahead (SVA) and perception of object motion were measured in 11 patients with downbeat ( n=6) and upbeat ( n=5) nystagmus. Upward deviations of SVA (median +5.2°) were found in downbeat nystagmus, and downward deviations (median −7.8°) in upbeat nystagmus. SVA was deviated toward the slow phase of the vertical nystagmus in the pitch plane and associated with increased fore-aft body sway. Perception of object motion was more severely impaired for vertical (particularly for motion in the direction of slow nystagmus phases) than for horizontal directions in both downbeat and upbeat nystagmus. Impairment of motion perception in the vertical pitch plane of the VOR is beneficial to the extent that it alleviates disturbing oscillopsia due to the involuntary retinal slip. Thus, our findings confirm the hypothesis that downbeat and upbeat nystagmus reflect a central tone imbalance of the VOR in the vertical pitch plane with ocular motor, postural, and perceptual manifestations.

Tracking multiple nonrigid objects in video sequences

This paper presents a method to track multiple nonrigid objects in video sequences. First, we present related works on tracking methods. Second, we describe our proposed approach. We use the notion of target to represent the perception of object motion. To handle the particularities of nonrigid objects we define a target as an individually tracked moving region or as a group of moving regions globally tracked. Then we explain how to compute the trajectory of a target and how to compute the correspondences between known targets and moving regions newly detected. In the case of an ambiguous correspondence we define a compound target to freeze the associations between targets and moving regions until a more accurate information is available. Finally we provide an example to illustrate the way we have implemented the proposed tracking method for video-surveillance applications.

Motion processing for saccadic eye movements during the visually induced sensation of ego-motion in humans

During ego-motion an observer is often faced with the task of controlling his heading direction while simultaneously registering the movement of objects in order to avoid possible obstacles. Psychophysical experiments have shown that the detection of moving objects is impaired by concurrent ego-motion. We investigated the interaction between ego-motion and object-motion by examining the latencies of saccades executed to moving targets under a visually induced sensation of ego-motion. Saccadic latencies increased during this sensation, with a global or non-retinotopic effect of optic flow on motion detection. Furthermore, separating stereoscopically the moving target and the optic flow into foreground and background, respectively, still resulted in increased latencies. We propose that an inhibitory influence of the perception of self-motion exists on the perception of object-motion. These results support a model of space constancy which strives to create a stable world during locomotion.

Cortical mechanisms for visual perception of object motion and position in space

The present review is aimed at analyzing and discussing some of the cortical mechanisms possibly involved in the perception of object motion and object localization in the visual field. A comprehensive approach to these topics would be beyond the scope of this work. The highest priority, therefore, will be given to the cortical machinery involved in these processes, while very little (or nothing at all) will be said on the possible role played by subcortical structures such as the lateral geniculate nucleus and the superior colliculus which, albeit not directly involved in perception, might contribute to it.

Object motion perception during ego-motion: Patients with a complete loss of vestibular function vs. normals

Object motion perception was assessed in avestibular patients and normal controls. Two experiments were conducted, in which subjects were required to assess the motion of a visual stimulus with respect to earth. In the first experiment, we measured the velocity at which a briefly presented (200 ms) grating was perceived as earth fixed, while the subject maintained fixation on a visual target fixed relative to the body, during whole-body yaw rotation (VOR suppression). In this experimental setup, the influence of the semicircular canal signals on object motion perception was evaluated. The avestibular patients judged the grating to be stationary with respect to earth, when it was moving at the same velocity as their body, whereas for normal controls, the grating was perceived as stationary when it moved at a velocity slower than their body motion, but greater than zero. The difference between the two subject groups was significant, and showed the strong contribution of the vestibular system to object motion perception. Similarly, a measurement of the velocity at which a grating was perceived as stationary was obtained during smooth pursuit eye movements. In this experiment the contribution of the efference copy of the oculomotor signal and proprioceptive signals to object motion perception were assessed. As with the first experiment, the normal controls displayed a more veridical sense of object motion perception than the patients, although the difference was only just significant. We suggest that the difference could be an adaptive change in the patients perception of motion, which allows them to reduce the effects of oscillopsia.

Detection thresholds for object motion and self-motion during vestibular and visuo-oculomotor stimulation

We compared the detection threshold for object motion with that of self-motion in space in healthy human subjects. Stimuli consisted of horizontal rotations of subjects' body with a fixation spot kept in fixed alignment with their heads (vestibular stimulus), rotation of the fixation spot relative to the stationary subjects (visuo-oculomotor stimulus), and a combination thereof by applying rotations of subjects' body relative to the stationary object (sinusoidal oscillations, 0.025–0.4 Hz). Two series of experiments were performed. 1) One group of subjects was instructed to attend to, and to indicate the occurrence of, either object or self-motion. 2) A second group was instructed not only to detect the occurrence of a perception, but also to qualify it either as object motion or self-motion, depending on which modality dominated perceptually. With either instruction it was found that all three stimulus conditions could evoke both, either an object motion perception or a self-motion perception. The detection thresholds of both perceptions were essentially similar. Thresholds were highest with the vestibular stimulus, intermediate with the stimulus combination, and lowest with the visuo-oculomotor stimulus. The vestibular threshold depended on stimulus frequency, in that it decreased with increasing frequency. Thereby, it became similar to the visuo-oculomotor one, which was essentially constant across frequency. Probability of occurrence of the perceptions in the first experimental series was considerably higher than in the second series, suggesting an important role of attentional mechanisms. In the second series, percent frequency of occurrence of veridical perception (object motion with visuo-oculomotor stimulus, self-motion with stimulus combination) was at chance level (50%) at low stimulus frequency, but was augmented considerably at high frequency. We assume that the latter effect is brought about by a visual-vestibular conflict measure by which the visual stimulus (light spot) is qualified as representing either a moving object or a spatial reference for self-motion. While at suprathreshold stimulus intensities the conflict can determine perception magnitude, at threshold levels its influence is restricted mainly on the probability of occurrence of object and self-motion perception.

Visual and Nonvisual Contributions to Perceived Ego-Motion Studied with a New Psychophysical Method

The perception of ego-velocity (PEV) during sinusoidal linear acceleration (otolith stimulation) is investigated with a psychophysical method proposed by Wertheim (1990;1). This method is based on the threshold for object motion perception measured during ego-motion. In a first experiment, PEV was measured both with and without illumination of the experimental room. It was shown that, for the particular frequency and amplitude of ego-motion used, PEV in the light approached physical ego-velocity, whereas in darkness PEV was significantly smaller than physical ego-velocity. In a second experiment the PEV was measured again without illumination of the experimental room. It was found that in response to a sinusoidal ego-velocity stimulus, PEV was sinusoidal as well with a gain of 0.8 and a phase-lead of 4 degrees at 0.15 Hz.

Ego- and object-motion perception: Where does it take place?

Ego- and object-motion perception: Where does it take place?

Size-distance invariance: kinetic invariance is different from static invariance.

The static form of the size-distance invariance hypothesis asserts that a given proximal stimulus size (visual angle) determines a unique and constant ratio of perceived object size to perceived object distance. A proposed kinetic invariance hypothesis asserts that a changing proximal stimulus size (an expanding or contracting solid visual angle) produces a constant perceived size and a changing perceived distance such that the instantaneous ratio of perceived size to perceived distance is determined by the instantaneous value of visual angle. The kinetic invariance hypothesis requires a new concept, an operating constraint, to mediate between the proximal expansion or contraction pattern and the perception of rigid object motion in depth. As a consequence of the operating constraint, expansion and contraction patterns are automatically represented in consciousness as rigid objects. In certain static situations, the operation of this constraint produces the anomalous perceived-size-perceived-distance relations called the size-distance paradox.

Role of vestibular and neck inputs for the perception of object motion in space

The contribution of vestibular and neck inputs to the perception of visual object motion in space was studied in the absence of a visual background (in the dark) in normal human subjects (Ss). Measures of these contributions were obtained by means of a closed loop nulling procedure; Ss fixed their eyes on a luminous spot (object) and nulled its actual or apparent motion in space during head rotation in space (vestibular stimulus) and/or trunk rotation relative to the head (neck stimulus) with the help of a joystick. Vestibular and neck contributions were expressed in terms of gain and phase with respect to the visuo-oculomotor/joystick feedback loop which was assumed to have almost ideal transfer characteristics. The stimuli were applied as sinusoidal rotations in the horizontal plane (f = 0.025-0.8 Hz; peak angular displacements, 1-16 degrees). (1) During vestibular stimulation, Ss perceived the object, when kept in fixed alignment with the moving body, as moving in space. However, they underestimated the object motion; the gain was only about 0.7 at 0.2-0.8 Hz and clearly decreased at lower stimulus frequencies, while the phase exhibited a small lead. (2) During pure neck stimulation (trunk rotating relative to the stationary head), the object, when stationary, appeared to move in space counter to the trunk excursion. This neck-contingent object motion illusion was small at 0.2-0.8 Hz, but increased considerably with decreasing frequency, while its phase developed a small lag. (3) Vestibular, neck, and visuo-oculomotor effects summed linearly during combined stimulations. (4) The erroneous vestibular and neck contributions to the object motion perception were complementary to each other, and the perception became about veridical (G approximately 1, phi approximately 0 degree), when both inputs were combined during head rotation with the trunk stationary. The results are simulated by an extended version of a computer model that previously had been developed to describe vestibular and neck effects on human perception of head motion in space. In the model, the perception of object motion in space is derived from the superposition of three signals, representing "object to head" (visuo-oculomotor; head coordinates), "head on trunk" (neck; trunk coordinates), and "trunk in space" (vestibular-neck interaction; space coordinates).

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.

Infants' sensitivity to effects of gravity on visible object motion.

A preference method probed infants' perception of object motion on an inclined plane. Infants viewed videotaped events in which a ball rolled downward (or upward) while speeding up (or slowing down). Then infants were tested with events in which the ball moved in the opposite direction with appropriate or inappropriate acceleration. Infants aged 7 months, but not 5 months, looked longer at the test event with inappropriate acceleration, suggesting emerging sensitivity to gravity. A further study tested whether infants appreciate that a stationary object released on an incline moves downward rather than upward; findings again were positive at 7 months and negative at 5 months. A final study provided evidence, nevertheless, that 5-month-old infants discriminate downward from upward motion and relate downward motion in videotaped events to downward motion in live events. Sensitivity to certain effects of gravity appears to develop in infancy.

Perception & Control of Self-Motion

Contents: Part I:Phenomena, Problems, & Terms. R. Warren, Preliminary Questions for the Study of Egomotion. D.H. Owen, Lexicon of Terms for the Perception and Control of Self-Motion and Orientation. Part II:Visual Aspects. J.J. Koenderink, Some Theoretical Aspects of Optic Flow. K. Nakayama, Properties of Early Motion Processing: Implications for the Sensing of Egomotion. V. Cornilleau-P r s, J. Droulez, Three-Dimensional Motion Perception: Sensorimotor Interactions and Computational Models. L. Wolpert, Field-of-View Information for Self-Motion Perception. G.J. Andersen, Segregation of Optic Flow Into Object and Self- Motion Components: Foundations for a General Model. Part III:Vestibular & Multisensory Aspects. A.J. Benson, Sensory Functions and Limitations of the Vestibular System. A.H. Wertheim, Visual, Vestibular, and Oculomotor Interactions in the Perception of Object Motion During Egomotion. T. Mergner, W. Becker, Perception of Horizontal Self-Rotation: Multisensory and Cognitive Aspects. Part IV:Skill & Control Aspects. H. Mittelstaedt, Basic Solutions to the Problem of Head-Centric Visual Localization. D.H. Owen, Perception & Control of Change in Self-Motion: A Functional Approach to the Study of Information and Skill. J.M. Flach, G. Lintern, J.F. Larish, Perceptual Motor Skill: A Theoretical Framework. W.A. van de Grind, Smart Mechanisms for the Visual Evaluation and Control of Self-Motion. R.J.A.W. Hosman, J.C. van der Vaart, Motion Perception and Vehicle Control. G.L. Zacharias, An Estimation/Control Model of Egomotion. Part V:Special Environmental Aspects. H.E. Ross, Orientation and Movement in Divers. D.N. Lee, Getting Around With Light or Sound. G. Jansson, Non-Visual Guidance of Walking. L.R. Young, M. Shelhamer, Weightlessness Enhances the Relative Contribution of Visually-Induced Self-Motion. Part IV:Self-Motion and the Perception & Control of the Environment. J.S. Lappin, Perceiving the Metric Structure of Environmental Objects from Motion, Self-Motion and Stereopsis. R.E. Shaw, P.N. Kugler, J. Kinsella-Shaw, Reciprocities of Intentional Systems.

An Acceleration Illusion Caused by Underestimation of Stimulus Velocity during Pursuit Eye Movements: Aubert–Fleischl Revisited

When the eyes pursue a fixation point that sweeps across a moving background pattern, and the fixation point is suddenly made to stop, the ongoing motion of the background pattern seems to accelerate to a higher velocity. Experiment I showed that this acceleration illusion is not caused by the sudden change in (i) the relative velocity between background and fixation point, (ii) the velocity of the retinal image of the background pattern, or (iii) the motion of the retinal image of the rims of the CRT screen on which the experiment was carried out. In experiment II the magnitude of the illusion was quantified. It is strongest when background and eyes move in the same direction. When they move in opposite directions it becomes less pronounced (and may disappear) with higher background velocities. The findings are explained in terms of a model proposed by the first author, in which the perception of object motion and velocity derives from the interaction between retinal slip velocity information and the brain's 'estimate' of eye velocity in space. They illustrate that the classic Aubert-Fleischl phenomenon (a stimulus seems to be moving slower when pursued with the eyes than when moving in front of stationary eyes) is a special case of a more general phenomenon: whenever we make a pursuit eye movement we underestimate the velocity of all stimuli in our visual field which happen to move in the same direction as our eyes, or which move slowly in the direction opposite to our eyes.