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PubMed1999

Condylar cartilage response to continuous passive motion in adult guinea pigs: A pilot study.

This article reports on the development and testing of a continuous passive motion device suitable for experimental animals and on the effect of 1 week of continuous passive motion on the thickness of the condylar cartilage in adult guinea pigs. Continuous passive motion is currently used for postsurgical joint therapy and consists of moving a synovial joint passively and constantly through its normal range of motion. In this study continuous passive motion was applied to the temporomandibular joints of two experimental animals for 7 hours per day for 5 days. Two animals were restrained for the same amount of time that the experimental animals were on the continuous passive motion machines (control group 1), and two animals were allowed normal cage activity (control group 2). Six weeks later all animals were sacrificed. Each mandibular condyle was sectioned sagitally, and routine histologic sections were prepared with hematoxylin-eosin stain. Microscopic examination of the mandibular condylar cartilage of the animals placed on continuous passive motion showed a marked increase in thickness compared with the condylar cartilage found on the control animals. The condylar cartilage of the animals placed on continuous passive motion averaged 345 microm, and the controls averaged 232 microm. These findings demonstrate the application of continuous passive motion in an experimental model and provide interesting information regarding the response of the mandibular condyle to increased motion. More studies are necessary to further investigate the effect of continuous passive motion on the condylar cartilage.

Animals↗
PubMed1999

Motion sickness in public road transport: the effect of driver, route and vehicle.

Relationships between vehicle motion and passenger sickness have been investigated in a survey of 3256 passengers travelling on 56 mainland UK bus or coach journeys. Vehicle motion was measured throughout all journeys, yielding over 110 h of six-axis coach motion data from five types of coach and 17 different drivers. Overall, 28.4% of passengers reported feelings of illness, 12.8% reported nausea and 1.7% reported vomiting during coach travel. Passenger nausea and illness ratings increased with increased exposure to lateral coach motion at low frequencies (< 0.5 Hz). Motion in other axes correlated less well with sickness, although there were some intercorrelations between the motions in the different axes. Sickness levels among passengers were greater with drivers who drove to produce higher average magnitudes of fore-and-aft and lateral vehicle motion. Nausea occurrence was greater on routes classified as being predominantly cross-country where magnitudes of lateral vehicle motion were significantly higher. Lateral motion and motion sickness increased from the front to the rear of each vehicle. No significant differences in sickness were found between the five different vehicle types used in the study. The applicability of a motion sickness dose model to these data is discussed.

Humans↗
PubMed2003

Human cortical object recognition from a visual motion flowfield.

Moving dots can evoke a percept of the spatial structure of a three-dimensional object in the absence of other visual cues. This phenomenon, called structure from motion (SFM), suggests that the motion flowfield represented in the dorsal stream can form the basis of object recognition performed in the ventral stream. SFM processing is likely to contribute to object perception whenever there is relative motion between the observer and the object viewed. Here we investigate the motion flowfield component of object recognition with functional magnetic resonance imaging. Our SFM stimuli encoded face surfaces and random three-dimensional control shapes with matched curvature properties. We used two different types of an SFM stimulus with the dots either fixed to the surface of the object or moving on it. Despite the radically different encoding of surface structure in the two types of SFM, both elicited strong surface percepts and involved the same network of cortical regions. From early visual areas, this network extends dorsally into the human motion complex and parietal regions and ventrally into object-related cortex. The SFM stimuli elicited a face-selective response in the fusiform face area. The human motion complex appears to have a central role in SFM object recognition, not merely representing the motion flowfield but also the surface structure of the motion-defined object. The motion complex and a region in the intraparietal sulcus reflected the motion state of the SFM-implicit object, responding more strongly when the implicit object was in motion than when it was stationary.

Adult↗
PubMed2003

Eye movement, vection, and motion sickness with foveal and peripheral vision.

BACKGROUND: Both motion sickness and the illusion of self-motion (i.e., vection) can be induced by moving visual scenes. The results of a previous study imply that motion sickness is primarily dependent on visual motion in foveal vision while vection is primarily dependent on motion in peripheral vision. HYPOTHESIS: It was hypothesized that similar motion sickness would be produced when tracking a single moving dot and a full screen of moving dots, but that vection would be greater when tracking multiple moving dots. METHOD: Sixteen subjects viewed moving images presented on a virtual reality head-mounted display. In one condition a single dot moved from left to right at 27 degrees x s(-1) over a distance of 18 degrees before returning instantly to its starting point. This motion was repeated continuously. In a second condition, five horizontal rows of dots, each 18 degrees apart, moved continuously across the screen at 27 degrees x s(-1); subjects were instructed to track each dot in the central row as it passed. RESULTS: In both conditions, there were nystagmic eye movements with an approximate amplitude of 18 degrees at 27 degrees x s(-1). Vection differed significantly between the two conditions, with more vection in the condition with five rows of dots. Subjects experienced motion sickness symptoms with both the single moving dot and the five rows of dots, with no significant difference in sickness between the two conditions. Subject ratings of motion sickness and vection were not correlated with each other in either of the two conditions. CONCLUSIONS: Motion sickness and vection can vary independently. Vection appears to be influenced by peripheral vision, as there was an increase in vection with full-field stimulation. Motion sickness induced by moving visual scenes may be influenced by foveal visual stimulation or by eye movements, as these were the same in both conditions.

Eye Movements↗
PubMed1991

The response of area MT and V1 neurons to transparent motion.

An important use of motion information is to segment a complex visual scene into surfaces and objects. Transparent motions present a particularly difficult problem for segmentation because more than one velocity vector occurs at each local region in the image, and current machine vision systems fail in these circumstances. The fact that motion transparency is prevalent in natural scenes, and yet artificial systems display an inability to analyze it, suggests that the primate visual system has developed specialized methods for perceiving transparent motion. Also, the currently prevalent model of physiological mechanisms for motion-direction selectivity employs inhibitory interactions between neurons; such interactions would silence neurons under transparent conditions and render the visual system blind to transparent motion. To examine how the primate visual system solves this transparency problem, we recorded the activity of direction-selective cells in the first (area V1) and in a later (area MT) stage in the cortical motion-processing pathway in behaving monkeys. The visual stimuli consisted of random dot patterns forming single moving surfaces, transparent surfaces, and motion discontinuities. We found that area V1 cells responded to their preferred direction of movement even under transparent conditions, whereas area MT cells were suppressed under the transparent condition. These data suggest a simple solution to the transparency problem at the level of area V1. More than one motion vector can be represented at a single retinal location by different subpopulations of neurons tuned to different directions of motion; these subpopulations may represent the early stage for segmenting different, transparent surfaces. The results also suggest that facilitatory mechanisms, which unlike inhibitory interactions are largely unaffected by transparent conditions, play an important role in direction selectivity in area V1. The inhibitory interactions for different motion directions for area MT neurons may contribute to a mechanism for smoothing or averaging the velocity field, computations thought to be necessary for reducing noise and interpolating moving surfaces from sparse information.

Animals↗
PubMed1994

Non-Fourier motion analysis.

It has been realized for some time that the visual system performs at least two general sorts of motion processing. First-order motion processing applies some variant of standard motion analysis (i.e. spatiotemporal Fourier energy analysis) directly to stimulus luminance, whereas second-order motion processing applies standard motion analysis to one or another grossly non-linear transformation of stimulus luminance. We have developed a method for disentangling the different sorts of mechanisms that may operate in human vision to detect second-order motion. This method hinges on an empirical condition called transition invariance that may or may not be satisfied by a family psi of textures. Any failure of this condition indicates that more than one mechanism is involved in detecting the motion of stimuli composed of the textures in psi. We have shown that the family of sinusoidal gratings oriented orthogonally to the direction of motion and varying in contrast and spatial frequency is transition invariant. We modelled the results in terms of a single-channel motion computation. We have new results indicating that a specific class of textures differing in texture element density and texture element contrast decisively fails the test of transition invariance. These findings suggest that in addition to the single second-order motion channel required by our earlier results there exists at least one other second-order motion channel. We argue that the preprocessing transformation used by this channel is a pointwise non-linearity that maps stimulus contrasts of absolute value less than some relatively high threshold tau onto 0, but increases with magnitude of c-tau for contrasts. c of absolute value greater than tau.

Animals↗
PubMed1996

Friction and stem stiffness affect dynamic interface motion in total hip replacement.

Large cyclic movements between the femoral stem and bone during the first weeks after total hip arthroplasty may hamper bone ingrowth and adversely affect the eventual success of the arthroplasty. Little is known, however, about the magnitude of the motions and its relationship to design and surgical factors. A two-dimensional finite element model of a cementless prosthesis inserted into the proximal femur was constructed to study the effects of two mechanical variables--the stiffness of the implant and the coefficient of friction between bone and implant--on the magnitude of the motions. We investigated the influences of these variables on the subsidence of the prosthesis, the magnitudes of the cyclic motions, and the level of the interface stresses. The presence of friction reduced cyclic motions by about 85% compared with a frictionless interface. Once friction was assumed, varying the coefficient of friction had little effect. The effect of friction on the interface stress state and gross subsidence of the prosthesis was not as great as on cyclic motion. Implant stiffness also affected the magnitudes and distributions of the cyclic motions along the interface. A flexible stem generated motions about three to four times larger proximally than those of a stiff stem, which generated larger motions distally. The influence of stem stiffness on interface stresses and prosthetic subsidence was less than on cyclic motion. The location of the peak shear stresses at the interface around a bonded prosthesis corresponded to the location where cyclic interface motion was maximal for an unbonded prosthesis. However, no direct relationship was found between the magnitudes of peak stresses and the amplitudes of cyclic motions.

Elasticity↗
PubMed1989

Motion perception prominence alters anticipatory slow eye movements.

Perceived motion may be a stimulus for anticipatory slow eye movements. To test this possibility, the production of anticipatory slow eye movements in humans was studied using apparent motion stimuli. Short range apparent motion was produced with random dot stimuli and the anticipatory slow eye movements were isolated from the smooth pursuit responses by occasionally including trials in which the random dot stimulus did not appear. Long range apparent motion was produced with subjective contour stimuli. Both short range and long range apparent motion were found to be effective stimuli for anticipatory slow eye movements. The prominence of perceived motion was altered by changing the spatiotemporal displacement intervals in the short range apparent motion stimuli. Changing the subjective contours also changed the motion percepts of the long range apparent motion stimuli. With both stimuli, the peak anticipatory slow eye velocities that were achieved decreased as the prominence of the motion percepts decreased, while the time-course of the anticipatory responses were similar under the different conditions. These findings indicate that the expectation of perceived motion is necessary for anticipatory slow eye movements.

Adult↗
PubMed2003

Isolating motion responses in visual evoked potentials by preadapting flicker-sensitive mechanisms.

Onset of visual motion evokes a component in the EEG, the motion onset VEP. Exploring its motion specificity with a direction-specific adaptation paradigm, previous work demonstrated that less than 50% of the motion onset VEP represents actual motion detection. Here, we tested whether preadaptation of flicker-sensitive mechanisms can help to isolate motion-specific responses in the VEP. Flicker preadaptation was accomplished by limiting dot lifetime in the random-dot kinematograms that we used to study the direction specificity of motion adaptation. With unlimited dot lifetime, motion adaptation reduced the VEP amplitude to 35% (adapted direction) and 50% (opposite direction). With the shortest dot lifetime (40 ms), motion adaptation reduced the amplitude to 55% (adapted direction) and 70% (opposite direction). These findings suggest that random-dot kinematograms with short dot lifetimes could improve the investigation of human motion processing, be it in electrophysiology or other fields. While such stimuli successfully preadapt flicker-related components, they still evoke a sizable response, of which an estimated 70% is motion-specific.

Electrooculography↗
PubMed2005

Motion adaptation: net duration matters, not continuousness.

Motion processing is strongly adaptable. Adaptation strength generally increases with motion duration. Little is known, though, about the effect of motion onsets and offsets, which might be relevant if adaptation is not based on motion duration per se, but on the recent cumulated activity of motion-processing mechanisms. Thus, we presented intermittent motion with three different onset rates for adaptation. The duty cycle was kept constant at 33% while the rate of motion onsets was either 1.4, 2.8, or 5.6 per second. Stationary stimuli and continuous motion were used as reference conditions. The amplitude of the N2 component of human motion visual evoked potentials was used to quantify adaptation. All three onset rates induced virtually identical amounts of adaptation (occipitally, P=0.71; occipito-temporally, P=0.27), suggesting that the continuousness of the stimulus does not play an important role in motion adaptation. This was confirmed by measuring the motion aftereffect psychophysically.

Adaptation, Physiological↗
PubMed1998

Superiority of triple-detector single-photon emission tomography over single- and dual-detector systems in the minimization of motion artefacts.

A patient motion-related artefact is one of the most important artefacts in single-photon emission tomography (SPET) imaging. This study evaluated the effect of the number and configuration of SPET detectors on motion artefacts. The following acquisition conditions were simulated based on original 360 degrees projection images: (1) single-detector 180 degrees rotation (S180), (2) a dual-detector rectangular (L-shaped) 180 degrees acquisition (D180L), (3) dual-detector cameras mounted opposite each other with 360 degrees acquisition (D360) and (4) triple-detector 360 degrees acquisition (T360). The motion artefacts were introduced using a syringe and a myocardial phantom. Clinical cases with technetium-99m methoxyisobutylisonitrile and thallium-201 studies were analysed to confirm the validity of this phantom simulation. The effect of continuous alternate rotation acquisition and summing the projections on the reduction of motion artefacts was investigated in each model. The effect of motion depended on the number and the configuration of the SPET detectors. A 1-pixel (6.4 mm) motion in the S180, D180L and D360 models generated only slight artefacts, and a 2-pixel motion led to an apparent decrease in activity or created hot areas in the myocardium. On the other hand, a T360 rotation created few artefacts even with a 2-pixel motion of the last quarter of the projections. Despite the difference in attenuation with 201Tl and 99mTc, similar artefact patterns were observed with both radionuclides in selected patient model studies. Continuous alternate rotation could reduce artefacts caused by less than a 2-pixel motion. In conclusion, calculating the average of the sum of the projections of triple-detector 360 degrees rotations with alternate rotation is the best method to minimize motion artefacts. This "averaging" effect of motion artefacts is a key to this simulation.

Gamma Cameras↗
PubMed1989

Saccadic suppression of low-level motion.

We measured the detection of motion before, during and after a saccade to explore the effects of a saccade on motion perception. To isolate the low-level motion mechanism, the stimulus was a random-dot field displaced by small distance (0.3 deg) within a stationary frame. The displacement signaled motion clearly if eyes were fixated, but for the displacement during a saccade, motion was not detected whether the displacement was defined in spatial coordinates (expt 1) or in retinal coordinates (expt 2). Since motion could be seen with ISIs longer than the duration of a saccade (expt 3), the suppression cannot be attributed to visual loss during the saccade. Experiment 3 also showed that motion was never seen for a displacement that occurred during a saccade, even though the random dots were replaced by a uniform field during the eye movement thereby eliminating any masking effect of the sweep of the image across the retina. The purpose of the saccadic suppression of motion may be to block out unreliable motion signals that would be produced by a saccade. Since saccade distances are very often greater than the maximum distance over which the low-level motion mechanism can produce accurate direction discrimination for fine textures, motion signals would generally indicate false directions if they were not suppressed.

Eye Movements↗
PubMed1990

ISI produces reverse apparent motion.

A moving random-dot stimulus was presented in two sequential frames separated by an interstimulus interval (ISI) during which the field was spatially uniform with luminance equal to either the average luminance of the stimulus field (grey) or that of the black dots (black). In Experiment 1, black ISIs did not affect perception of motion direction but grey ISIs produced motion in the direction opposite to the physical displacement (reverse motion). In Experiment 2, the contrast of the stimulus was reversed simultaneously with the displacement of the random-dot fields so that reverse motion would be seen with no ISI [Anstis & Rogers, Vision Research, 15, 957, 1975]. In this condition, grey ISIs reversed the reverse motion to produce a veridical perception. Finally, in Experiment 3, we examined whether the negative image that follows the stimulus offset was the source of the reversal in motion direction. A gradual offset of the stimulus necessarily reduces the amplitude of the negative response at stimulus offset and also reduced the frequency of seeing reverse motion, suggesting that the apparent reversal of motion direction with ISI can be attributed to the negative phase of a biphasic impulse response function. A simulation of the temporal response to the displacements of random-dot fields demonstrated that the negative phase of a biphasic impulse response function is sufficient to produce the reverse motion. We therefore claim that there is a significant biphasic temporal response function that precedes the analysis of motion in the visual system. This indicates that the overall temporal response function of the visual system is the result of a cascade of functions from early through late stages and that only a portion of the overall temporal response function can be attributed to stages involved in motion analysis.

Contrast Sensitivity↗
PubMed1992

Visual persistence of figures defined by relative motion.

In order to measure visual persistence of figures that were solely defined by relative motion (motion-defined figures or motion figures), random-dot kinematograms were used to form stimulus figures in the two-frame, missing element task introduced by Di Lollo, V. (1977 Nature, 257, 241-243). Experiment 1 showed that motion-defined figures persisted for about 130 msec after the termination of the stimulus presentation (i.e. after the dots stopped moving). This was similar to but several tens of milliseconds longer than the visual persistence of figures which were defined by a luminance difference (luminance-defined figures or luminance figures) in the same random-dot pattern. Since motion detectors are not found in the retina or lateral geniculate in primates, our results strongly suggest that visual persistence is not only a retinal phenomenon but also a cortical one. Experiment 2 investigated the possible influence of motion aftereffects on the visual persistence of motion figures. The results showed that coherent movement of the dots over the whole display after the stimulus offset did not reduce the visual persistence of motion figures, suggesting that the source of this persistence is not a motion aftereffect. In Experiment 3, visual persistence for the motion-defined figures was shown to be longer than that for luminance-defined figures independently of the contrast of the stimulus figure as long as the stimuli could be seen clearly enough. This suggests that different mechanisms are involved in the visual persistence of motion-defined and luminance-defined figures.

Afterimage↗
PubMed1993

Spatial localization of motion-defined and luminance-defined contours.

Thresholds for the vernier alignment of contours defined by luminance and coherent random-dot motion were measured. The luminance-defined contours were localized with a precision better than the receptor grain, while the motion-defined contours were localized more poorly than this limit. When motion-defined and luminance-defined targets were matched for dot density, vernier thresholds were equivalent at low densities. When the targets were also equated for perceived contrast, the vernier thresholds became equivalent at higher densities as well. These results suggest that the precision with which motion-defined contours are localized is contrast and sample limited. Next, the localization mechanism for motion-defined targets was investigated. Length summation limits were similar for motion-defined and luminance-defined targets, suggesting that these targets could be localized by a common mechanism. Vernier targets were then flanked by two additional bars. Motion-defined flanks interfered with the localization of motion-defined targets and luminance-defined flanks interfered with the localization of luminance-defined targets. However, motion-defined and luminance-defined bars did not interact to produce spatial interference. This result indicates that the mechanisms for localizing luminance-defined and motion-defined targets are independent. We suggest that parallel mechanisms govern the vernier localization of motion-defined and luminance-defined targets.

Contrast Sensitivity↗
PubMedDate not supplied

Spatiotemporal properties of motion perception for random-check contrast modulations.

To clarify the mechanism of detecting the motion of contrast modulations, the spatiotemporal properties of direction discrimination for contrast motion were examined. The stimulus was a microbalanced random stimulus [Chubb and Sperling (1988) Journal of the Optical Society of America A 5, 1986-2007], termed random-window kinematogram (RWK), a shifting random checkerboard pattern in which each check was either a patch of random dots (uncorrelated between frames) or a patch of uniform gray having the mean luminance of the random dots. The effect of exposure duration (ED) on RWK discrimination could be described as stimulus onset asynchrony (SOA) dependency when EDs of the first and second frames were the same, but the performance was better than predicted from SOA when the first ED was short while the second was long. RWK could be seen at longer inter-stimulus intervals than random-dot kinematogram (RDK) having similar stimulus parameters (e.g. check size, effective contrast). Incoherent motion (e.g. reversed phi) could be seen for RWK. Maximum displacement limit (Dmax) for RWK was comparable to that of RDK, but it increased in proportion to check size, while Dmax for RDK did not. These results suggest that the contrast motion mechanism extracts motion locally, and involves a correlation-type motion extraction stage similar to the luminance motion mechanism. In addition, the spatial ranges of the contrast motion detectors are comparable to those of the luminance motion detectors, but their temporal range is larger. The contrast motion mechanism is more scale-invariant than the luminance motion mechanism.

Contrast Sensitivity↗
PubMed1995

Speed discrimination of motion-in-depth using binocular cues.

Although it is well known that motion-in-depth can be detected using binocular cues, it is not known whether those cues can be used to judge the speed of an object moving in depth. There are at least two possible binocular cues that could be used by the visual system to calculate three dimensional (3-D) speed: the rate of change of binocular disparity, or a comparison of the speeds of motion in the two eyes. We tested which of these cues is used to discriminate the speed of motion-in-depth. First, speed discrimination was measured for a dot moving away from the observer in depth (along the z-axis) and for a random dot stereogram in which a central square moved away from the observer in depth. These stimuli contained both disparity and monocular motion cues. Speed discrimination thresholds were as good for 3-D motion as for monocular sideways motion. Second, a dynamic random dot stereogram (in which the random dot pattern was replaced by a new dot pattern every frame) was used to remove consistent monocular cues. 3-D speed discrimination was now very poor, suggesting that the rate of change of disparity is not a good cue for 3-D speed. Finally, we tested whether observers were able to use the monocular motion cue from one eye to perform the speed discrimination task, or whether there had to be a comparison of the two eyes' monocular cues. By adding a small x-axis velocity component (with random direction) to the z-axis motion, it was possible to disrupt the monocular motion signals without altering the speed of the motion in 3-D. This manipulation did not disrupt the observers' performance, suggesting that monocular speed cues were not being used independently but that there was a comparison of monocular motion signals from the two eyes.

Cues↗
PubMed1994

Directional anisotropy of motion sensitivity across the visual field.

There is an implicit assumption in most models of movement direction perception that sensitivity to motion is directionally isotropic, i.e. equal for movement in all directions. However, most previous research on directional effects on human motion perception have measured responses (e.g. manual reaction times) to suprathreshold stimuli rather than motion sensitivity. I investigated this possibility by measuring monocular sensitivity to motion coherence in small field random-dot kinematograms with global leftwards or rightwards motion as a function of eccentricity along the horizontal meridian in each eye of six observers. Although foveal motion sensitivity was isotropic, small but significant differences (about 0.1 log units) in sensitivity in favour of centripetal motion were observed at eccentricities between 5.0 and 12.5 deg. Motion anisotropy was significantly larger in the temporal than the nasal visual hemifield. In a second experiment, motion coherence thresholds for upwards and downwards movement were measured foveally and at +/- 5 deg on the vertical meridian. At the fovea, no difference in sensitivity to upwards vs downwards motion was observed but these vertical axis thresholds were significantly higher than foveal thresholds for movement along the horizontal axis. Directional anisotropy in favour of centripetal motion was present in the inferior visual field but directional isotropy was found for the superior visual field. Perhaps this generally heightened sensitivity to centripetal directions may function normally to facilitate figure/ground segmentation in the presence of centrifugally-moving background contours that typically accompany forward locomotion.

Adolescent↗