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PubMed1995

Motion integration across differing image features.

To interpret the projected image of a moving object, the visual system must integrate motion signals across different image regions. Traditionally, researchers have examined this process by focusing on the integration of equally ambiguous motion signals. However, when the motions of complex, multi-featured images are measured through spatially limited receptive fields, the resulting motion measurements have varying degrees of ambiguity. In a series of experiments, we examine how human observers interpret images containing motion signals of differing degrees of ambiguity. Subjects judged the perceived coherence of images consisting of an ambiguously translating grating and an unambiguously translating random dot pattern. Perceived coherence of the dotted grating depended upon the degree of concurrence between the velocities of the grating terminators and dots. Depth relationships also played a critical role in the motion integration process. When terminators were suppressed with occlusion cues, coherence increased. When dots and gratings were presented at different depth planes, coherence decreased. We use these results to outline the conditions under which the visual system uses unambiguous motion signals to interpret object motion.

Depth Perception↗

PubMed1995

The effect of flicker on foveal and peripheral thresholds for oscillatory motion.

This study evaluated the influence of superimposed luminance flicker on the detection of oscillatory motion. Thresholds for oscillatory motion were determined in the fovea and at 2, 6 and 25 deg in the right field for a small luminous target with and without sinusoidal luminance flicker. At the fovea, flicker modulation up to 80% at frequencies from 1.5 to 9 Hz had no effect on motion detection, except for oscillatory motion at a frequency of 8 Hz, for which thresholds were elevated by about 0.2 log units. In the periphery, flicker elevated motion thresholds up to 0.3-0.4 log units at low and moderate frequencies of oscillation at all locations tested. However, both foveal and peripheral motion thresholds were unaffected by flicker when the luminance of the target was reduced. The absence of a robust effect of target flicker on motion thresholds may be accounted for in part by the comparison of activity across a large population of motion-detecting neurons with different direction preferences. Another contributing factor may be the existence of foveal velocity- and position-detecting mechanisms with similar sensitivities.

Female↗

PubMed1995

Detecting a trajectory embedded in random-direction motion noise.

Human observers can easily detect a signal dot moving, in apparent motion, on a trajectory embedded in a background of random-direction motion noise. A high detection rate is possible even though the spatial and temporal characteristics (step size and frame rate) of the signal are identical to the noise, making the signal indistinguishable from the noise on the basis of a single pair of frames. The success rate for detecting the signal dot was as high as 90% when the probability of mismatch from frame-to-frame, based on nearest-neighbor matching, was 0.3. Control experiments showed that trajectory detection is not based on detecting a "string" of collinear dots, i.e. a stationary position cue. Nor is a trajectory detected because it produces stronger signals in single independent motion detectors. For one thing, trajectory detection improves with increases in duration, up to 250-400 msec, a duration longer than the integration typically associated with a single motion detector. For another, the signal dot need not travel in a straight line to be detectable. The signal dot was as reliably detected when it changed its direction a small amount (about 30 deg or less) each frame. Consistent with this, circular paths of sufficiently low curvature were as detectable as straight trajectories. Our data suggest that trajectory motion is highly detectable in motion noise because the component local motion signals are enhanced when motion detectors with similar directional tuning are stimulated in a sequence along their preferred direction.

Cues↗

PubMed1996

The interpretation of visual motion: evidence for surface segmentation mechanisms.

The independent motions of objects in a visual scene are commonly manifest as overlapping retinal motions. A consequence of this overlap is the creation of spurious retinal image features--such as corners and terminated contours--that bear no direct relation to the motions of the objects that give rise to them. To reconstruct object motions, these emergent features must be distinguished from the retinal motions of real object features. This process can be studied using visual stimuli known as plaid patterns, which provide a laboratory archetype for the ubiquitous real-world circumstance of two surfaces with overlapping retinal projections. By adjusting luminance relationships in a plaid pattern it is possible to influence the perceptual interpretation of image features, such that they are seen as either an emergent consequence of occlusion or as real variations in surface reflectance. In the former case, the plaid is most likely to be to perceived as two independently moving surfaces, whereas the latter generally elicits a percept of a single moving surface. This dependence of motion perception on luminance configuration can be viewed as evidence for the involvement of surface segmentation mechanisms, which distinguish between real and emergent image features by promoting a depth-ordered neural representation of surfaces. An alternative interpretation, which does not demand such depth-ordering and feature classification, asserts that the effect of luminance configuration can be accounted for by attendant variations in the distribution of moving Fourier components. To evaluate these two proposed mechanisms, we designed novel plaid stimuli in which surface segmentation cues could be varied independently of changes in the distribution of Fourier components. Perceived motion was found to be highly correlated with the presence of appropriate segmentation cues and uncorrelated with the distribution of Fourier components. These results refute the Fourier components hypothesis, and they support our proposal that surface segmentation plays a critical role in the interpretation of visual motion signals.

Contrast Sensitivity↗

PubMed1995

Isolation and characteristics of a steady-state visually-evoked potential in humans related to the motion of a stimulus.

We have examined the visual potential evoked by two motion stimuli. In the first stimulus (termed coherent motion) a random-dot pattern oscillated between phases of coherent and incoherent ("snowstorm") motion, and in the second a random-dot pattern alternated in direction of motion (termed direction change). We found that the response to the coherent motion stimulus is low-pass with respect to speed, has low contrast sensitivity and increases steadily with the contrast of the stimuli. The direction change visually-evoked potential (VEP) is band-pass with respect to speed, has high contrast sensitivity but then saturates and even reduces as the stimulus contrast is raised above 0.1. The behaviour of the direction change VEP is similar in nature to results from psychophysical experiments of motion perception and to the known properties of directionally selective cells of the cortex. On the other hand the behaviour of the coherent motion VEP suggests this may not be mediated by a mechanism specific to motion.

Contrast Sensitivity↗

PubMed1995

Attentional modulation of adaptation to two-component transparent motion.

We have studied the effects of voluntary attention on the induction of motion aftereffects (MAEs). While adapting, observers paid attention to one of two transparently displayed random dot patterns, moving concurrently in opposite directions. Selective attention was found to modulate the susceptibility to motion adaptation very substantially. To measure the strength of the induced MAEs we modulated the signal-to-noise ratio of a real motion signal in a random dot pattern that was used to balance the aftereffect. Results obtained for adapting to single motion vectors show that the MAE can be represented as a shift of the psychometric function for motion direction discrimination. Selective attention to the different components of transparent motion altered the susceptibility to adaptation. Shifting attention from one component to the other caused a large shift of the psychometric curves, about 70-75% of the shift measured for the separate components of the transparent adapting stimulus. We conclude that attention can differentiate between spatially superimposed motion vectors and that attention modulates the activity of motion mechanisms before or at the level where adaptation gives rise to MAEs. The results are discussed in light of the role of attention in visual perception and the physiological site for attentional modulation of MAEs.

Adaptation, Physiological↗

PubMed1983

An appraisal of the value of vitamin B12 in the prevention of motion sickness.

Unpublished reports have suggested that hydroxycobalamin (B12, i.m.) prevents motion sickness. Some biomedical evidence supports this contention in that B12 influences the metabolism of histidine and choline; dietary precursors to neurotransmitters with established roles in motion sickness. Susceptibility to motion sickness was evaluated after B12 (1000 micrograms, i.m.). Subjects initially completed vestibular function and motion sickness susceptibility tests to establish normal vestibular function. The experimental motion stressor was a modified coriolis sickness susceptibility test. Subjects executed standardized head movements at successively higher RPM until a malaise III endpoint was reached. Following two baseline tests with this motion stressor, subjects received a B12 injection, a second injection two weeks later, and a final motion sickness test three weeks later. No significant differences in susceptibility were noted after B12. Hematological parameters revealed no B12 deficiency before injection. The possibility that patients with B12 deficiencies are more susceptible to motion sickness cannot be ruled out.

Aerospace Medicine↗

PubMed1995

Processing of visual motion direction in the fronto-parallel plane in the stationary or moving observer.

To examine the effect of concurrent self-motion on the perception of the direction of object-motion, random-dot kinematograms were employed in which the strength of the directional signal was manipulated by varying the percentage of coherently moving pixels. The subject's task was to indicate the motion direction of briefly presented displays while undergoing whole body rotations with angular accelerations of 0, 5, 15, or 45 degrees/s2. The perception of the direction of visual motion in the horizontal plane was impaired only when visual and vestibular motion directions were incongruous. The impairment increases with both increasing angular acceleration and decreasing percentage of coherently moving pixels. For object-motion in the vertical plane, an impairment was found for both congruous and incongruous combination of visual and vestibular stimulation, although not as pronounced for the latter (i.e., visual upward, vestibular downward stimulation, and vice versa). These results are discussed in terms of postnatal development and neurophysiological optimization processes resulting from intersensory 'updating' through every-day experience of object-motion during self-motion.

Acceleration↗

PubMed1991

8-OH-DPAT does not interfere with habituation to motion-induced emesis in cats.

Experiments were performed to determine if suppression of motion-induced emesis (motion sickness) by 8-OH-DPAT altered the development or retention of habituation to the motion stimulus. Cats received 8-OH-DPAT followed by provocative motion on three consecutive treatment days. A drug-free test on the fourth day resulted in an incidence of emesis that was not different from that obtained on the fourth consecutive day of drug-free motion testing. Three consecutive days of treatment with 8-OH-DPAT without motion had no effect on the incidence of motion sickness on the fourth day. It was concluded that suppression of motion sickness by 8-OH-DPAT does not alter the acquisition or retention of habituation.

8-Hydroxy-2-(di-n-propylamino)tetralin↗

PubMed1992

Flexor digitorum profundus tendon excursions during controlled motion after flexor tendon repair in zone II: a prospective clinical study.

Intratendinous metal markers were used to study flexor digitorum profundus tendon excursions during early controlled motion with dynamic flexion traction and to evaluate their significance for results after flexor tendon repair in zone II. The mean excursion was 1 mm along the middle phalanx and 5.6 mm along the proximal phalanx. This corresponded to a mean excursion per 10 degrees of controlled distal and proximal interphalangeal joint motion of 0.3 and 1.2 mm, respectively. Compared to active motion, controlled motion of the distal interphalangeal joint mobilized the tendon with an efficiency of 36% and controlled motion of the proximal interphalangeal joint mobilized the tendon with an efficiency of 90%. Controlled-motion excursions induced by the distal interphalangeal joint along the middle phalanx had little influence on subsequent active range of motion in the distal interphalangeal joint, whereas excursions along the proximal phalanx (for which the proximal interphalangeal joint was largely responsible) did have a significant influence on subsequent total active interphalangeal range of motion.

Adolescent↗

PubMed1993

Motion after metacarpophalangeal joint reconstruction in rheumatoid disease.

The outcome of reconstruction of the rheumatoid metacarpophalangeal joint may deteriorate with time, especially with respect to active motion. This study assesses active finger motion after crossed intrinsic transfer and Swanson implant arthroplasty at increasing durations of follow-up to determine the effect of time. In a total of 58 patients, 21 hands had the crossed intrinsic transfer operation and 49 had the arthroplasty. Follow-up time averaged 6 years for the crossed intrinsic transfers and 21 months for the arthroplasties. Measurement of metacarpophalangeal, proximal interphalangeal, and distal interphalangeal joint active motion at each follow-up interval were analyzed by the univariate repeated measures analysis of variance method. After crossed intrinsic transfer the overall average active range of motion decreased significantly (18 degrees) at the metacarpophalangeal joint. Proximal interphalangeal and distal interphalangeal average range of motion significantly increased during the first 5 years as a result of increases in flexion. After implant arthroplasty, the overall average metacarpophalangeal range of motion analysis at the different follow-up intervals showed that the metacarpophalangeal average range of motion significantly increased during the first 2 years and then gradually declined through the duration of follow-up. Active proximal interphalangeal flexion was also significantly increased during the first 2 postoperative years. The effects of metacarpophalangeal joint reconstruction on active finger joint motion are related to the duration of postoperative follow-up; this concept should be considered when one is planning metacarpophalangeal joint reconstruction in rheumatoid patients.

Arthritis, Rheumatoid↗

PubMed1994

Pseudofractures of the mandible secondary to motion artifact.

The case of a patient with a false-positive fracture on the panoramic view of the mandible is presented. The patient motion produced a spurious image that perfectly mimicked a fracture without any evidence of motion. To better assess motion artifact, panoramic views of a "phantom" human skull were developed with movement during the exposure. These radiographs were analyzed with the assistance of a radiologist, and diagnostic features of motion artifact are discussed. Some radiographs were created by movement that mimicked fractures without the telltale signs of motion artifact. These "motion pseudofractures" are diagnosed clinically if the examiner knows that motion can mimic fractures, and all x-ray findings are carefully correlated with clinical findings. Diagnosis of a motion pseudofracture will avoid the additional expense and time of a specialty consultation.

Adult↗

PubMedDate not supplied

The incidence and effects of motion sickness among medical attendants during transport.

Motion sickness is a common and often debilitating problem. The purpose of this study was to determine the incidence and effects of the motion sickness syndromes, the Nausea and Sopite Syndromes, among medical transport personnel. Members of the Transport Teams of the University of North Carolina Hospitals completed a questionnaire to identify a history of susceptibility to motion sickness. An additional questionnaire evaluated each individual for symptoms of motion sickness during transport. The Digit Span Test portion of the Mini-Mental Status Examination (DST-MMSE) was used to evaluate cognitive function after transport. Control data on each subject were obtained by testing during nontransport shifts. The Nausea Syndrome was observed during transport in 46% of subjects; 65% experienced symptoms consistent with the Sopite Syndrome. Pretransport surveys were predictive of the Nausea Syndrome, but not of the Sopite Syndrome. The Nausea Syndrome was related to subjective assessments of the severity of motion experienced; the Sopite Syndrome did not correlate with the severity of motion. The DST-MMSE scores after transport were significantly lower than scores during nontransport periods in 85% of personnel. We conclude that transport personnel are susceptible to motion sickness manifested by both the Nausea Syndrome and the Sopite Syndrome. The presence of motion sickness is associated with a significant decline in performance on tests of attention and concentration.

Air Ambulances↗

PubMed2004

Annular geometry and motion in human ischemic mitral regurgitation: novel assessment with three-dimensional echocardiography and computer reconstruction.

BACKGROUND: Annular geometry and motion in functional ischemic mitral regurgitation are incompletely understood. Three-dimensional echocardiography demonstrates saddle-shaped annular geometry, but standard methodology does not enable quantification of annular motion. Therefore, a novel technique using three-dimensional echocardiography and computer software was used to characterize alterations in mitral annular geometry and motion in patients with ischemic mitral regurgitation. METHODS: We developed a computer program to reconstruct the mitral annulus based on spatial coordinates from three-dimensional echocardiography. Data were obtained at end-diastole and end-systole in 7 patients with ischemic mitral regurgitation and 5 normal control subjects. Mitral annular motion was quantified by calculating the displacement area of the annulus between end-diastole and end-systole. RESULTS: Comparison of ischemic mitral regurgitation and control patients revealed differences in annular geometry and motion at end-diastole. Annular perimeter was greater in ischemic mitral regurgitation patients (10.7 +/- 0.7 cm versus 8.6 +/- 0.2 cm in control group; p < 0.03), with increased intertrigonal distance in ischemic mitral regurgitation patients (2.8 +/- 0.3 cm versus 2.1 +/- 0.1 cm; p < 0.06). These changes resulted in increased annular orifice area in ischemic mitral regurgitation patients (9.1 +/- 1.2 cm2 versus 5.7 +/- 0.3 cm2; p < 0.03). Ischemic mitral regurgitation patients had altered annular motion, with reduced movement of the posterior annulus (5.4 +/- 0.7 cm2 versus 8.7 +/- 1.1 cm2; p < 0.03). CONCLUSIONS: Computer analysis of data obtained from three-dimensional echocardiography demonstrates altered annular geometry and motion in patients with ischemic mitral regurgitation. Patients with ischemic mitral regurgitation have annular dilatation, with an increase in anterior and posterior annular perimeters; this is accompanied by an increase in the intertrigonal distance and restriction of annular motion.

Aged↗

PubMed2005

Relation between motion sickness susceptibility and vasovagal syncope susceptibility.

Motion sickness is common in the population, especially in children, but its physiopathology is only partially understood and the true nature of the particular susceptibility of certain subjects remains completely unknown. Some symptoms of motion sickness, like pallor and cold sweating, are of an autonomic nature and the role of the autonomic nervous system in vasovagal syncope is well known. Our aim was therefore to study the relationship between motion sickness susceptibility and vasovagal syncope susceptibility. Questionnaires about susceptibility to motion sickness and to vasovagal syncope or presyncope in adulthood and childhood, filled in by 899 students (20.4 +/- 2.1 years, 405 men), were analysed. Motion sickness susceptibility in childhood was 31.1% and in adulthood 7.9% (p < 0.001). Vasovagal syncope susceptibility in childhood was 36.4% and in adulthood 33.9% (NS). A relationship between motion sickness susceptibility in adulthood and vasovagal syncope susceptibility in childhood and adulthood (p = 0.004 and 0.005, respectively) was found. Despite the limitations of a retrospective study this relationship between motion sickness susceptibility and vasovagal syncope susceptibility may indicate that a common mechanism exists, explaining the particular susceptibility of some subjects to both disorders. This paradigm may prove useful in better understanding the true nature of motion sickness and vasovagal syncope.

Aging↗

PubMed2004

Analysis of passive motion characteristics of the ankle joint complex using dual Euler angle parameters.

OBJECTIVE: To apply the dual Euler angles method to investigate the passive motion characteristics of the human ankle joint complex. DESIGN: Three-dimensional kinematic data of the ankle joint complex was collected from 10 knee-below foot cadaver specimens. BACKGROUND: Besides the Euler angles and screw axis methods, the dual Euler angles method has been proposed as an alternative approach to quantify general spatial human joint motion. The dual Euler angles method provides a way to combine rotational and translational joint motions and to interpret motions in Cartesian coordinate systems, which can avoid the problems caused by the use of the joint coordinate system due to non-orthogonality. METHODS: A non-metal experimental setup was fabricated to generate motion in foot cadaver specimens. The kinematic data during passive dorsiflexion-plantarflexion was measured using an electromagnetic tracking device. RESULTS: The kinematic coupling characteristics and the respective contribution of the ankle joint and the subtalar joint to the gross motion of the foot with respect to the shank were analyzed based on dual Euler angle parameters. The results obtained in this study are generally in agreement with the observations reported previously. CONCLUSIONS: The dual Euler angles method is suitable for analyzing the motion characteristics of the ankle joint complex. The motion at the ankle joint complex involves rotations about and translations along three axes.

Algorithms↗

PubMed2004

Motion-sensitive neurones in V5/MT modulate perceived spatial position.

Until recently, it was widely believed that object position and object motion were represented independently in the visual cortex. However, several studies have shown that adaptation to motion produces substantial shifts in the perceived position of subsequently viewed stationary objects. Two stages of motion adaptation have been proposed: an initial stage at the level of V1 and a secondary stage thought to be located in V5/MT. Indeed, selective adaptation can be demonstrated at each of these levels of motion analysis. What remains unknown is which of these cortical sites are involved in modulating the positional representation of subsequently viewed objects. To answer this question directly, we disrupted cortical activity by using transcranial magnetic stimulation (TMS) immediately after motion adaptation. When TMS was delivered to V5/MT after motion adaptation, the perceived offset of the test stimulus was greatly reduced. In marked contrast, TMS of V1 had no effect on the changes that normally occur in perceived position after motion adaptation. This result demonstrates that the anatomical locus at which motion and positional information interact is area V5/MT rather than V1/V2.

Brain Mapping↗

PubMed2005

Separate processing of different global-motion structures in visual cortex is revealed by FMRI.

The visual system has the remarkable ability to extract several types of meaningful global-motion signals, such as radial motion, translation motion, and rotation, for different visual functions and actions. In the monkey brain, different groups of cells in MST respond best to different types of global motion [1, 2] whereas in lower cortical areas including MT, no such differential responses have been found. Here, we show that an area (or areas) lower than MST in the human brain [3] responds to different types of global motion. A series of human functional magnetic resonance imaging (fMRI) experiments, in which attention was controlled for, indicated that the center of radial motion activates the corresponding location in the V3A representation, whereas translation motion activates mainly in a more peripheral representation of V3A. These results suggest that in the human brain, V3A is an area that differentially responds according to the type of global motion.

Adult↗