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PubMed1997

The perception of motion and structure in structure-from-motion: comparisons of affine and Euclidean formulations.

I investigated the discrimination of rigid from nonrigid structure and the perception of affine stretches along the line of sight [Norman & Todd (1993). Perception and Psychophysics, 53, pp. 279-291]. Investigations of performance at discriminating rigid from nonrigid structure showed that performance improved when number of views and amount of simulated three-dimensional nonrigidity increased. Investigations of rotations about the vertical which include affine stretches along the line of sight compared Euclidean interpretations of affine-stretching stimuli to human perception. These Euclidean interpretations were obtained from a simple algorithm which recovered structure and motion from this limited class of stimuli under the assumption that distances to the axis of rotation did not change. The algorithm predicted that stretches along the line of sight would be perceived as nearly rigid and have variable angular velocity. These predictions were supported by subjects' reports of occurrences of nonrigidity and minima of angular velocity. The Euclidean algorithm also provided measures of nonrigidity and motion coherence, and experimental results were consistent with a prediction of when perception of nonrigidity would be independent of perception of coherence. The results are discussed relative to the advantages and shortcomings of both the affine and Euclidean approaches to structure-from-motion.

Algorithms↗
PubMed1998

Motion blur and motion sharpening: temporal smear and local contrast non-linearity.

Blurred images may appear sharper when drifting than when stationary. But, paradoxically, moving sharp edges may appear more blurred. To resolve this paradox, the perceived sharpness of drifting, blurred, square wave gratings was compared with that of their static analogues over a range of speeds, blurs and spatial frequencies. Both motion blur and motion sharpening occurred, depending upon the physical blur of the patterns. For large extents of blur (> 10 min arc) moving patterns always appeared sharper than their static analogues, but for small blurs (< 10 min arc) moving edges appeared more blurred than stationary ones. We present a quantitative model for the distortion of waveforms in motion based on two factors: (i) visual temporal integration that smears moving images, and (ii) a local contrast non-linearity that increasingly sharpens the effective profile of edges as speed and contrast increase. We suggest that a plausible account of the speed-dependent non-linearity is the differential recruitment of M and P cells at different speeds.

Contrast Sensitivity↗
PubMed2000

A hierarchical structure of motion system revealed by interocular transfer of flicker motion aftereffects.

Interocular transfer of the motion aftereffect (MAE) has been extensively investigated for the purpose of analysing the binocularity of the underlying motion mechanism. Previous studies unanimously reported that the transfer of the classical static MAE is partial, but there is a controversy as to whether the transfer of the flicker MAE (MAE measured using counterphase gratings) is partial or perfect. To gain insight into the discrepancy between studies, we investigated whether the interocular transfer of the flicker MAE is influenced by the MAE measurement method, retinal eccentricity and attention. Our results showed that the transfer was perfect or nearly so when the MAE duration was measured in the central visual field with observers paying attention to the adaptation stimulus, but the transfer was partial when the MAE nulling strength was measured, when the MAE duration was measured in the peripheral visual field, or when the observers' attention was distracted by a secondary task. These results not only resolve discrepancies between previous studies, but also suggest that the flicker MAE reflects adaptation at multiple stages in the hierarchical architecture of motion processing.

Adaptation, Physiological↗
PubMed1998

The initiation and sequence of digital joint motion. A three-dimensional motion analysis.

We studied the initiation and sequence of digital joint motion during unrestricted flexion and extension using a 3-D motion analysis of all fingers moving simultaneously. Our results showed that motion started in a single joint in 83%, of flexion and 80%, of extension cycles. The DIP joint initiated flexion and extension in the index, middle, and ring fingers, but in the little finger, flexion started in the PIP joint, and extension in the MP joint. The two most frequent sequences of joint movement during flexion of the three radial fingers were DIP-PIP-MP and PIP-DIP-MP. The two most frequent sequences during extension of the three radial fingers were DIP-MP-PIP followed by DIP-MP/PIP. In the little finger, however, the most frequent sequences during flexion were PIP-DIP-MP followed by DIP-PIP-MP and during extension, DIP-MP/PIP followed by PIP/DIP-MP.

Adult↗
PubMed2003

Relationship between motion VEP and perceived velocity of gratings: effects of stimulus speed and motion adaptation.

The N200 amplitude of the motion-onset VEP evoked by a parafoveal grating of variable speed (0.25-13.5 degrees/s), constant spatial frequency (2 cpd), contrast (4%), and direction (horizontally rightward) was studied before and after adaptation to a stationary or drifting grating (1 or 4 degrees/s). Psychophysical measurements were made simultaneously of the perceived speed. In the unadapted condition the slope of the N200 amplitude versus speed function is positive, but lower for high compared to low speeds. The N200 amplitude increases slightly after stationary adaptation. An increase in perceived speed is also evident after stationary adaptation. This increase is more pronounced for low compared to high speeds. Motion adaptation reduces N200 amplitudes over the entire speed range, whereas perceived speeds change from under-estimation to over-estimation when the speed exceeds 1.8 degrees/s after 1 degree/s adaptation and 4.5 degrees/s after 4 degrees/s adaptation. The simultaneous evaluation of motion VEP and psychophysical results supports the view that the neurons generating the N200 component are also involved in speed perception. The data suggest the existence of a limited number (three or more) speed channels.

Adaptation, Physiological↗
PubMed1998

Cognitive motion extrapolation and cognitive clocking in prediction motion task.

An interruption paradigm was used to measure judgments that rely on cognitive extrapolation of approach and lateral motion. In some conditions the pattern of errors was consistent with that obtained with time-to-contact (TTC) judgments measured with a prediction motion (PM) task. Also, the slope of the relationship between estimated and actual TTC in judgments of approaching objects decreased when visual information about the environment between the observer and the display was minimized. Moreover, the accuracy of relative duration judgments of visual (but not auditory) stimuli decreased when a PM task was performed concurrently. Results are consistent with the notion that PM tasks involve cognitive motion extrapolation rather than solely a clocking process that counts down TTC.

Analysis of Variance↗
PubMed1977

Visual motion aftereffect induced by simulated rectilinear motion.

Visual motion aftereffect characteristics comparable to those associated with rotary and translatory movement of a test field are demonstrated for simulated rectilinear motion of the observer. The intensity and time duration of the phenomenon are shown to be positively correlated. The implications of this for individual observers are considered. The results of this experiment are correlated with those for adaptation and for recovery from adaptation that were obtained from the same group of observers. The findings are shown to support the hypothesis that visual motion affereffect is a manifestation of the adaptation recovery function of velocity sensitive mechanisms.

Adult↗
PubMed2000

Mechanisms for seeing transparency-from-motion and orientation-from-motion.

Structure-from-motion (SFM) perception is hypothesised to be mediated by units that sense the near-far relationships in transparency-from-motion (TFM) and orientation-from-motion (OFM). The frequency of subjective reversals during observation of ambiguous SFM displays is considerably decreased when either the direction of rotation or the surface orientation is oscillated during the inspection. Such manipulations impede adaptation of units selectively sensitive to TFM and OFM. The results show that both OFM and TFM units are direction-selective, and that the reversal rate is unaffected by reducing TFM to zero; and support the view that depth order, when both TFM and OFM are present, is estimated by common neural units.

Adaptation, Physiological↗
PubMed1993

The effect of marker placement deviations on spinal range of motion determined by video motion analysis.

BACKGROUND AND PURPOSE: Spinal range of motion (ROM) is an important indicator of spinal function and is used in the determination of disability and compensation. One technology that has been used to assess spinal ROM is video motion analysis. No studies, however, have been done to investigate the effects of marker placement on ROM. The purpose of this study was to investigate the effect of deviations in reflective marker placement on ROM measurements obtained via video motion analysis. METHODS: A model of the spine was constructed and used to obtain ROM measurements from three segments of the model to isolate error from marker placement without the confounding effects of subject error. A standard placement and six altered placements were used to determine the effect of moving reflective markers on ROM. RESULTS: Results indicated statistically significant effects of marker placement for a number of flexion/extension and lateral side-bending ROM measurements. When the mean differences were compared with data obtained in human test-retest studies with the same equipment, the differences from a 2.5-cm marker deviation did not appear to be clinically meaningful. CONCLUSION AND DISCUSSION: We conclude that small marker deviations (2.5 cm) are not likely to adversely affect clinical information obtained when using this type of apparatus.

Disability Evaluation↗
PubMed1993

Intrasubject reliability of spinal range of motion and velocity determined by video motion analysis.

BACKGROUND AND PURPOSE: The purpose of this study was to investigate the repeatability of spinal range of motion (ROM) and movement velocity measurements of patients with chronic low back pain, using a two-dimensional motion analysis system. This apparatus uses reflective markers placed on anatomical landmarks and video digitization to derive ROM measurements from three segments of the spine and associated velocities through the respective ROMs. SUBJECTS: Forty-two patients with chronic LBP underwent ROM and movement velocity testing. METHODS: Each subject was tested twice without removal of the markers to minimize error contribution from differences in marker placement. RESULTS: Results indicated that both the ROM measures and the velocity measures were highly repeatable. Intraclass correlations for the ROM measures ranged from .77 to .96. Velocity measures were also reliable, with intraclass correlation coefficients ranging from .75 to .97. CONCLUSION AND DISCUSSION: Overall, the results seem to indicate that the video motion analysis system used in this study yields repeatable ROM and velocity measures on a clinical population. In practice, however, the measures may reflect greater errors due to the need of examiners to relocate markers at different testing sessions. These systems also offer distinct advantages over other means of obtaining ROM and velocity measures. The results of this study indicate that these measures may be obtained without undue concern for measurement artifact due to the instrumentation reliability.

Adult↗
PubMed1997

The effect of a plaster cast on lumbosacral joint motion. An in vivo assessment with precision motion analysis system.

STUDY DESIGN: This study was conducted to assess the effect of a plaster cast on the mobility of the lumbosacral joint in 10 patients with chronic low back pain. During static and dynamic exercises, movements between the proximal vertebra (L4 or L5) and the sacrum were registered in 10 patients without a support and after the application of a plaster cast, and with and without unilateral hip immobilization, respectively. OBJECTIVES: To investigate whether plaster casts actually immobilize the lumbosacral joint. SUMMARY OF BACKGROUND DATA: The presumed stabilizing effect of a lumbar orthosis on the lumbosacral joint has been the subject of many studies in the past years, and contradictory reports have been published. METHODS: The measurements were performed by means of Precision Motion Analysis System, an optoelectronic three-dimensional motion analysis system using infrared light. The patients were asked to perform maximal spinal flexion to extension, maximal pelvic tilt (static test conditions), and to walk within the measurement volume (dynamic test condition). This procedure was repeated with the patients wearing a plaster cast with and without unilateral hip fixation. Mobility was expressed in translations and rotations around three axes. For statistical analysis, repeated measurements two-way analysis of variance was used. RESULTS: Considerable rotations were found only in the sagittal plane. Both plaster casts appeared to decrease mobility during the static test conditions. During the dynamic test condition, however, no significant decrease of mobility of the lumbosacral joint by either of the casts could be observed. In both cast conditions, considerably more sagittal rotation was found during walking than with the other two exercises. CONCLUSION: In the sagittal plane, a plaster cast with or without unilateral hip immobilization can decrease motion during spinal flexion-extension. This stabilizing effect on the lumbosacral joint could not be observed during walking.

Adult↗
PubMed2005

Integration of geometric elements, Euclidean relations, and motion curves for parametric shape and motion estimation.

This paper presents an approach to shape and motion estimation that integrates heterogeneous knowledge into a unique model-based framework. We describe the observed scenes in terms of structured geometric elements (points, line segments, rectangles, 3D corners) sharing explicitly Euclidean relationships (orthogonality, parallelism, colinearity, coplanarity). Camera trajectories are represented with adaptative models which account for the regularity of usual camera motions. Two different strategies of automatic model building lead us to reduced models for shape and motion estimation with a minimal number of parameters. These models increase the robustness to noise and occlusions, improve the reconstruction, and provide a high-level representation of the observed scene. The parameters are optimally computed within a sequential Bayesian estimation procedure that gives accurate and reliable results on synthetic and real video imagery.

Algorithms↗
PubMed1995

Motion detectors and motion segregation.

The response of motion detectors necessarily confound image velocity with image structure. In particular, even a rigidly moving image (with a uniform velocity field) will give rise to non-uniform detector responses. A mathematical framework has been proposed on how to intrinsically compare motion detectors' responses so that their differences will reflect the true differences in image velocity (Zhang and Wu, Proc. Natl. Acad. Sci. USA 87, 7819-7823, 1990). Here, this notion of 'intrinsic differentiation' was implemented by introducing a gamma-matrix determined by the image spatial gradients. The perceptual phenomenon of random-dot motion segregation was successfully simulated.

Humans↗
PubMed2005

Effect of a novel motion desensitization training regime and controlled breathing on habituation to motion sickness.

To study whether controlled breathing, known to ameliorate motion sickness, speeds habituation to nauseogenic motion when used in a novel accelerated training regime, 30 participants (13 men, 17 women, ages 18-51 years) were randomized to either a Breathing group or a Control group. Randomization was balanced for rotation tolerance measured during a first exposure to off-vertical axis rotation (OVAR 72 degrees sec.(-1)). Participants subsequently received four exposures to OVAR in 1-hr. (accelerated training). The Breathing group followed taped instructions to control their breathing during training and when retested the next day. There was overall habituation with stimulus repetition, shown by an increase in tolerance for motion, a reduction in symptoms, and speeded recovery times on retesting. There was a tendency for greater habituation with controlled breathing.

Adolescent↗
PubMed1992

Properties of the recombination of one-dimensional motion signals into a pattern motion signal.

We have examined the human ability to determine the direction of movement of a variety of plaid patterns. The plaids were composed of two orthogonal sine-wave gratings. When the plaid components are of unequal spatial frequency or sometimes of unequal contrast, observers judge the direction of movement incorrectly. In terms of the two-stage model of Adelson and Movshon (1982), these errors may result from either a misjudgment in the perceived speeds of each of the components or a failure in the combination of one-dimensional component movements into a coherent direction of motion of the two-dimensional plaid pattern, or both. A comparison of the perceived direction of motion of plaids with the relative perceived speeds of the plaid component gratings suggest that both failures occur, but in different circumstances. The relative perceived speed of the plaid components was measured with a spatial and a temporal forced-choice technique, the former leading to larger differences. Our results support the notion that the visual system decomposes a moving plaid into oriented components and subsequently recombines the component motions.

Adult↗
PubMed1993

Stereo-motion cooperation and the use of motion disparity in the visual perception of 3-D structure.

When an observer views a moving scene binocularly, both motion parallax and binocular disparity provide depth information. In Experiments 1A-1C, we measured sensitivity to surface curvature when these depth cues were available either individually or simultaneously. When the depth cues yielded comparable sensitivity to surface curvature, we found that curvature detection was easier with the cues present simultaneously, rather than individually. For 2 of the 6 subjects, this effect was stronger when the component of frontal translation of the surface was vertical, rather than horizontal. No such anisotropy was found for the 4 other subjects. If a moving object is observed binocularly, the patterns of optic flow are different on the left and right retinae. We have suggested elsewhere (Cornilleau-Pérès & Droulez, in press) that this motion disparity might be used as a visual cue for the perception of a 3-D structure. Our model consisted in deriving binocular disparity from the left and right distributions of vertical velocities, rather than from luminous intensities, as has been done in classical studies on stereoscopic vision. The model led to some predictions concerning the detection of surface curvature from motion disparity in the presence or absence of intensity-based disparity (classically termed binocular disparity). In a second set of experiments, we attempted to test these predictions, and we failed to validate our theoretical scheme from a physiological point of view.

Acceleration↗
PubMed1991

Residual motion perception in a "motion-blind" patient, assessed with limited-lifetime random dot stimuli.

A neurological patient (L.M.) suffering a specific loss of visual motion perception (Zihl et al., 1983) due to extrastriate cortical damage was studied using random dot "limited-lifetime" stimuli with a direction discrimination task. With a stimulus like that of Newsome and Pare (1988), the patient exhibited a severe deficit for motion perception, only being able to perform well for very high values of coherence. Different versions of the stimulus were employed to separate out the effects of limited lifetime versus the effects of additive noise as coherence was lowered. When all "signal" dots had a fixed, specified value of lifetime, and varying percentages of "noise" dots were added, the patient showed a profound deficit. In contrast, a stimulus consisting of no noise dots at all, and signal dots having fixed values of lifetime, revealed relatively good performance for surprisingly brief dot lifetimes. Thus, it is the presence of noisy, incoherent dot motion, rather than brief lifetimes, that causes such poor performance on the stimulus of Newsome and Pare (1988). Most surprising was the finding that the presence of even very small percentages of stationary noise dots was sufficient to disrupt totally direction discrimination of moving signal dots. The findings reported here suggest that one major role of extrastriate cortical processing might be the interpretation of stimuli that suffer from an impaired signal-to-noise ratio; the most commonly encountered form of "noise" would presumably be contamination by irrelevant directional spatio-temporal frequency components.

Humans↗