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At least 1,441 records · Page 80Linked to original sources
PubMed2000

Anterior cervical fusion: a finite element model study on motion segment stability including the effect of osteoporosis.

STUDY DESIGN: Three-dimensional, nonlinear finite element models were used to evaluate the stability of the mid cervical spine after anterior fusion in patients with and without osteoporosis. OBJECTIVES: The objective of this study was to compare the change in flexibility of C5-C6 after anterior discectomy with both loose-fitting and tight-fitting fusion graft. SUMMARY OF BACKGROUND DATA: Many factors such as surgical technique, osteoporosis, and excess neck motion during the postoperative period may contribute to fusion failure. Knowledge about changes in biomechanical properties after the surgical procedure is important for selection of grafts with appropriate strength and for guiding patients in postoperative care and rehabilitation. METHODS: Analyses with anterior fusion models with both loose-fitting and tight-fitting graft were performed in a normal and an osteoporotic spine. The motion of the C5 vertebra in relation to the C6 vertebra were calculated, after multidirectional moment loads of 0.5 Nm combined with a compressive preload of 105 N. RESULTS: Loose-fitting graft produced both an increase and a decrease in motion under various external moment loads, with graft compressive stress below the compressive strength of the graft material. A reduction in motion was observed under all moment loads when a tight-fitting graft was used. The compressive stress in the tight-fitting graft was higher than the strength of the graft material. Osteoporosis increased the principal motions with both the loose-fitting graft and tight-fitting graft. Maximum increase in motion with a loose-fitting graft construct was observed under extension and axial torsion moment loads. CONCLUSIONS: Anterior discectomy and insertion of the loose graft resulted in increased motion. A tight-fitting graft is beneficial in reducing motion, but the stress within the graftincreases beyond the graft strength. The presence of osteoporosis was nominally significant when the graft was tight fitting.

Adult↗
PubMed2001

Maximal versus feigned active cervical motion in healthy patients: the coefficient of variation as an indicator for sincerity of effort.

STUDY DESIGN: Maximal and submaximal (feigned) cervical motions in healthy patients were compared. OBJECTIVE: To test the efficiency of the coefficient of variation in differentiating maximal (sincere) from submaximal (feigned) cervical motion in healthy patients. SUMMARY OF BACKGROUND DATA: Although limitation of cervical motion is a recognized impairment, no well-founded approach for verifying the degree to which a patient is maximizing his or her performance is available currently. METHODS: A new ultrasound-based system for three-dimensional motion analysis of the head was used to test 25 healthy patients (22 women and 3 men) ages 26 to 48 years. During the first test, (Test 1), the patients were asked initially to move the head maximally at a self-determined velocity in all the primary directions: flexion, extension, right and left rotation, and right and left lateral flexion. They then were presented with a short vignette describing a fictitious accident and asked, using the same protocol, to perform the same types of cervical motions as if they had experienced an injury. No further instructions were provided. A retest (Test 2) in reverse order (feigned effort first) took place 1 to 16 weeks (mean, 3.3 weeks) later. RESULTS: The range of motion and average velocity were significantly smaller (P = 0.0001) in the feigned than in the maximal performance in all directions and on both tests. Feigned range of motion and velocity also were significantly reduced in Test 2 (P = 0.006), as compared with those in Test 1 (P = 0.0001). The range of motion coefficient of variation in the feigned performance (CVf) remained stable on the retest, but was significantly larger on both tests (P < 0.001) than the corresponding CV derived from maximal performance (CVm). Furthermore, a case-by-case analysis showed that whereas the American Medical Association guidelines identified only 16% of the feigned cases, the use of CVf and CVm resulted in a corresponding rate of 87%. Tolerance intervals at 95% and 99% indicated total separation between the distributions of CVf and CVm, respectively. The average velocity-based CVf and CVm were not of a comparable differentiating power. CONCLUSIONS: This study indicates that in healthy patients, feigned performance may be differentiated from maximal (sincere) performance effectively and reproducibly using the coefficient of variation.

Adult↗
PubMed2002

Development and validation of a new technique for assessing lumbar spine motion.

STUDY DESIGN: Dynamic lumbar flexion-extension motions were assessed by an electrogoniometer and a videofluoroscopy unit simultaneously. OBJECTIVE: To develop and validate a new technique for the assessment of lumbar spine motion. SUMMARY OF BACKGROUND DATA: Spine instability, a clinical condition that is common but difficult to diagnose, has been suggested to involve a characteristic change in the relation between vertebrae during motion. Assessment of lumbar instability using functional radiographs is controversial. Information regarding dynamic spine kinematics in vivo is limited. METHODS: A lumbar spine motion analysis system was developed, and its reliability was assessed. Simultaneous total flexion range of motion and segmental motion of the lumbar spine were assessed in 30 healthy volunteers. Lumbar images were captured in 10 degrees intervals during flexion-extension. Intervertebral flexion-extension of each vertebral level was calculated. RESULTS: In flexion, the lumbar vertebrae flexed with a descending order from L1 to L5 throughout the motion. Conversely, the concavity of lumbar lordosis increased steadily in extension. No statistically significant difference in the pattern of motion was found between genders. CONCLUSIONS: The results from this study showed that the newly developed technique is reliable. It may have potential value for evaluating spine instability in clinical practice.

Adult↗
PubMed2002

Biomechanical study on the effect of cervical spine fusion on adjacent-level intradiscal pressure and segmental motion.

STUDY DESIGN: A biomechanical study was performed using cadaveric cervical spine specimens. OBJECTIVE: To determine the effect of cervical spine fusion on adjacent-level intradiscal pressure. SUMMARY OF BACKGROUND DATA: Clinical studies have reported that patients with spinal fusion are at greater risk of pathology and early disc degeneration at adjacent levels. It is hypothesized that eliminating motion at one level leads to hypermobility and increased forces at adjacent levels, thus increasing the rate of disc degeneration. METHODS: Six cadaveric cervical spine specimens were tested. Specimens were stabilized at T1 and loaded at C3 to 20 degrees of flexion and 15 degrees of extension. Intradiscal pressures and segmental motion at C4-C5 and C6-C7 were recorded first on intact specimens, and then after anterior cervical plating at C5-C6. Changes in intradiscal pressure and segmental motion were calculated and statistically analyzed using a paired Student t test. RESULTS: Intradiscal pressures were significantly increased during flexion at both adjacent levels. The pressure increased by 73.2% at C4-C5 (P = 0.002), and by 45.3% at C6-C7 (P = 0.006). Intradiscal pressures increased at both adjacent levels during extension, but not significantly. During flexion, segmental motion increased at both adjacent levels, with greater increases at C4-C5. During extension, segmental motion increased at both adjacent levels, with greater increases at C6-C7. CONCLUSIONS: Clinical studies have reported increased rates of disc degeneration at levels adjacent to fusion. It is believed that eliminating motion through fusion shifts the load to the adjacent levels, causing earlier disc degeneration. This study has shown that significant increases in intradiscal pressure and segmental motion occur at levels adjacent to fusion during normal range of motion. These results may partially explain the mechanism of early disc degeneration at levels adjacent to cervical spine fusion.

Biomechanical Phenomena↗
PubMed2003

Cervical disc replacement-porous coated motion prosthesis: a comparative biomechanical analysis showing the key role of the posterior longitudinal ligament.

STUDY DESIGN: Benchtop cadaveric biomechanical comparative testing and caprine animal model in vivo implantation. OBJECTIVE: To evaluate the role of the posterior longitudinal ligament in cervical arthroplasty and to understand the relative contribution of this ligament in nonfusion applications. SUMMARY OF BACKGROUND DATA: Rauschning refers to the posterior longitudinal ligament as "The Kleenex Ligament" due to its apparent anatomic insignificance. White and Panjabi found the posterior longitudinal ligament ranked only fourth in importance in tensile load-to-failure biomechanical testing. In the postoperative situation following anterior cervical diskectomy fusion, posterior longitudinal ligament integrity is overlooked by physicians because the entire disc space usually fuses into a homogeneous block of bone. PURPOSE: This biomechanical study was undertaken to determine the relative importance of the posterior longitudinal ligament following two different degrees of anterior decompression, anterior disc replacement, and anterior arthrodesis procedures. METHODS: A total of seven fresh frozen human cadaveric cervical spines (C3-C7) (mean age 68 +/- 19 years) were used for biomechanical testing. Each vertebra was equipped with three non-colinear light emitting diodes designed for detection by an optoelectronic motion measurement system (3020 Optotract System). To determine the multidirectional flexibility, six pure moments (flexion, extension, right + left lateral bending, right + left axial rotation) and axial compression were applied using a servohydraulic 858 Bionix testing device configured with a six-degree-of-freedom spine simulator. Range of motion was defined as the peak displacement from the initial neutral position to the maximum load, whereas the neutral zone represents the motion from the initial neutral position to the unloaded position at the beginning of the third cycle. Seven groups of (N = 7 each) constructs at C5-C6 were: 1) intact "native" C5-C6 level; 2) anterior diskectomy (posterior longitudinal ligament intact); 3) a Low Profile Porous Coated Motion cervical disc replacement; 4) posterior longitudinal ligament resected; 5) Porous Coated Motion cervical disc replacement fixed with anterior flanges and screws; 6) tricortical structural allograft; and 7) an anterior cervical translational plate + allograft. The caprine model was evaluated for suitability as an animal model with 12 goats undergoing C3-C4 anterior cervical Porous Coated Motion disc replacement. RESULTS: Group 2 (anterior diskectomy alone) was significantly more stable than Group 4 (anterior diskectomy + posterior longitudinal ligament resection) in flexion-extension, 18.7 +/- 4.76 degrees versus 24.8 +/- 4.42 degrees (P < 0.05) and in lateral bending, 5.9 +/- 1.79 degrees versus 10.7 +/- 2.8 degrees (P < 0.05). The comparison for the two conditions for axial rotation, 10.4 +/- 13.9 degrees versus 13.9 +/- 2.7 degrees, and axial compression, 1.19 +/-.98 degrees versus 1.52 +/- 1.14 degrees, showed the same trend. Twelve goats undergoing porous coated motion cervical disc replacement had no evidence of prosthesis loosening, neurologic complications, or experienced inflammatory reactions from particulate wear debris after 6 months of implantation. DISCUSSION: This study confirms the pivotal role of the posterior longitudinal ligament in postsurgical stability of the cervical spine following anterior diskectomy. This is because the lateral anulus, uncovertebral ligaments, and lateral capsular ligaments are stretched and plastically deformed in the surgical distraction process of restoring the disc space height following anterior surgical decompression. There should be a separate determination of the range of motion of cervical disc replacements depending of the integrity and the amount of the posterior longitudinal ligament that has been resected. CLINICAL RELEVANCE: There are two basic types of total knee replacements, posterior cruciate ligament-preserving and posterior cruciate ligament-sacrificing designs. In the cervical spine, an analogous situation exists biomechanically depending on whether the posterior longitudinal ligament needs to be removed in its entirety as part of the spinal cord decompression part of the procedure--it may be helpful to conceptually differentiate between posterior longitudinal ligament-preserving and posterior longitudinal ligament-sacrificing total cervical disc replacements.

Aged↗
PubMed2006

Cervical motion in patients with chronic disorders of the cervical spine: a reproducibility study.

STUDY DESIGN: Test-retest of cervical motion in patients with chronic disorders of the cervical spine. OBJECTIVES: To determine the reproducibility of cervical motion and examine the feasibility of its representation by a single parameter. SUMMARY OF BACKGROUND DATA: Reproducibility of cervical motion findings has been largely limited to normal subjects, leaving a conspicuous void regarding the measurement error in clinical groups. METHODS: There were 2 groups of 25 chronic patients with whiplash and degenerative changes of the cervical spine tested twice (4-7 days). Head movement was measured along the 6 directions, as well as during rotation out of flexion and extension (cervical degenerative changes only). RESULTS: Compared to normal subjects, both groups had a 25% to 35% reduction in cervical motion. High intraclass correlation coefficients (ICCs) (range 0.8-0.92) were derived for all directions. The ICCs for rotation out of flexion and extension were low. The relative standard error of measurement ranged from 15% to 28% for all directions, whereas the corresponding scores of the total cervical motion excursion were 10.6 (cervical degenerative changes) and 13.6% (whiplash). CONCLUSIONS: Judged by the ICCs cervical motion, findings were reproducible. However, in view of the measurement error as well as the homogenous reductions, total cervical range of motion should be considered a suitable parameter for interpretation of cervical motion limitations in these patients.

Adult↗
PubMed2006

Three-dimensional in vivo measurement of lumbar spine segmental motion.

STUDY DESIGN: Fifteen asymptomatic volunteers were externally rotated and CT scanned to determine lumbar segmental motion. OBJECTIVES: To measure three-dimensional segmental motion in vivo using a noninvasive measurement technique. SUMMARY OF BACKGROUND DATA: Spinal instability has been implicated as a potential cause of low back pain, especially, axial rotational instability. Typically, flexion-extension lateral radiographs were used to quantify instability, but inaccurately measured translations and inability to capture out-of-plane rotations are limitations. METHODS: Using a custom-calibrated rotation jig, L1-S1 CT reconstructions were created of volunteers in each of 3 positions: supine and left and right rotations of the torso with respect to the hips. Segmental motions were calculated using Euler angles and volume merge methods in three major planes. RESULTS: Segmental motions were small (< 4 degrees or 6 mm) with the greatest motions seen in axial rotation (range, 0.6 degrees to 2.2 degrees ), lateral bending (range, -3.6 degrees to 3.0 degrees ), and frontal translation (-1.2 mm to 5.4 mm). Largest motions were in the levels: L1-L2 to L3-L4. CONCLUSIONS: Complex coupled motions were measured due to external torsion and could be indicative of instability chronic patients with low back pain. The presented data provide baseline segmental motions for future comparisons to symptomatic subjects.

Adult↗
PubMed2001

Motion detection in human vision: a unifying approach based on energy and features.

Most studies of human motion perception have been based on the implicit assumption that the brain has only one motion-detection system, or at least that only one is operational in any given instance. We show, in the context of direction perception in spatially filtered two-frame random-dot kinematograms, that two quite different mechanisms operate simultaneously in the detection of such patterns. One mechanism causes reversal of the perceived direction (reversed-phi motion) when the image contrast is reversed between frames, and is highly dependent on the spatial-frequency content of the image. These characteristics are both signatures of detection based on motion energy. The other mechanism does not produce reversed-phi motion and is unaffected by spatial filtering. This appears to involve the tracking of unsigned complex spatial features. The perceived direction of a filtered dot pattern typically reflects a mixture of the two types of behaviour in any given instance. Although both types of mechanism have previously been invoked to explain the perception of motion of different types of image, the simultaneous involvement of two mechanisms in the detection of the same simple rigid motion of a pattern suggests that motion perception in general results from a combination of mechanisms working simultaneously on different principles in the same circumstances.

Energy Metabolism↗
PubMed2001

Detection of motion in hybrid PET/SPECT imaging based on the correlation of partial sinograms.

This paper describes a motion detection method specific to hybrid positron emission tomography/single photon emission computed tomography systems. The method relies on temporal fractionation of the acquisition into three data sets followed by an algorithm based on the cross correlation (CC) of partial sinograms from successive sets at different rotations of the camera. Spatial inconsistencies due to motion are detected by decreases in the CC between two sets. This permits to separate data into premotion and postmotion sets of consistent data that are reconstructed independently then registered and summed. Rigid motions greater than 1-cm translation or 10 degrees rotation were detected with this method from experimental data obtained by manually moving phantoms made of radioactive spheres as well as from a patient lung study corrupted by artificial motion. The different motion studies showed that the image contrast does not seem to be a limiting factor and that the motion is best detected when the gantry is parallel to the direction of motion. The registration and fusion of the reconstructed premotion and postmotion sets lead in all cases to a reduction of the motion artifacts and an increase in signal-to-noise ratio.

Algorithms↗
PubMed2004

Highly scalable video compression with scalable motion coding.

A scalable video coder cannot be equally efficient over a wide range of bit rates unless both the video data and the motion information are scalable. We propose a wavelet-based, highly scalable video compression scheme with rate-scalable motion coding. The proposed method involves the construction of quality layers for the coded sample data and a separate set of quality layers for the coded motion parameters. When the motion layers are truncated, the decoder receives a quantized version of the motion parameters used to code the sample data. The effect of motion parameter quantization on the reconstructed video distortion is described by a linear model. The optimal tradeoff between the motion and subband bit rates is determined after compression. We propose two methods to determine the optimal tradeoff, one of which explicitly utilizes the linear model. This method performs comparably to a brute force search method, reinforcing the validity of the linear model itself. Experimental results indicate that the cost of scalability is small. In addition, considerable performance improvements are observed at low bit rates, relative to lossless coding of the motion information.

Algorithms↗
PubMed2006

Concurrent 3-D motion segmentation and 3-D interpretation of temporal sequences of monocular images.

The purpose of this study is to investigate a variational method for joint multiregion three-dimensional (3-D) motion segmentation and 3-D interpretation of temporal sequences of monocular images. Interpretation consists of dense recovery of 3-D structure and motion from the image sequence spatiotemporal variations due to short-range image motion. The method is direct insomuch as it does not require prior computation of image motion. It allows movement of both viewing system and multiple independently moving objects. The problem is formulated following a variational statement with a functional containing three terms. One term measures the conformity of the interpretation within each region of 3-D motion segmentation to the image sequence spatiotemporal variations. The second term is of regularization of depth. The assumption that environmental objects are rigid accounts automatically for the regularity of 3-D motion within each region of segmentation. The third and last term is for the regularity of segmentation boundaries. Minimization of the functional follows the corresponding Euler-Lagrange equations. This results in iterated concurrent computation of 3-D motion segmentation by curve evolution, depth by gradient descent, and 3-D motion by least squares within each region of segmentation. Curve evolution is implemented via level sets for topology independence and numerical stability. This algorithm and its implementation are verified on synthetic and real image sequences. Viewers presented with anaglyphs of stereoscopic images constructed from the algorithm's output reported a strong perception of depth.

Algorithms↗
PubMed2006

Optimal temporal interpolation filter for motion-compensated frame rate up conversion.

Frame rate up conversion (FRUC) methods that employ motion have been proven to provide better image quality compared to nonmotion-based methods. While motion-based methods improve the quality of interpolation, artifacts are introduced in the presence of incorrect motion vectors. In this paper, we study the design problem of optimal temporal interpolation filter for motion-compensated FRUC (MC-FRUC). The optimal filter is obtained by minimizing the prediction error variance between the original frame and the interpolated frame. In FRUC applications, the original frame that is skipped is not available at the decoder, so models for the power spectral density of the original signal and prediction error are used to formulate the problem. The closed-form solution for the filter is obtained by Lagrange multipliers and statistical motion vector error modeling. The effect of motion vector errors on resulting optimal filters and prediction error is analyzed. The performance of the optimal filter is compared to nonadaptive temporal averaging filters by using two different motion vector reliability measures. The results confirm that to improve the quality of temporal interpolation in MC, the interpolation filter should be designed based on the reliability of motion vectors and the statistics of the MC prediction error.

Algorithms↗
PubMed2004

Layered motion segmentation and depth ordering by tracking edges.

This paper presents a new Bayesian framework for motion segmentation--dividing a frame from an image sequence into layers representing different moving objects--by tracking edges between frames. Edges are found using the Canny edge detector, and the Expectation-Maximization algorithm is then used to fit motion models to these edges and also to calculate the probabilities of the edges obeying each motion model. The edges are also used to segment the image into regions of similar color. The most likely labeling for these regions is then calculated by using the edge probabilities, in association with a Markov Random Field-style prior. The identification of the relative depth ordering of the different motion layers is also determined, as an integral part of the process. An efficient implementation of this framework is presented for segmenting two motions (foreground and background) using two frames. It is then demonstrated how, by tracking the edges into further frames, the probabilities may be accumulated to provide an even more accurate and robust estimate, and segment an entire sequence. Further extensions are then presented to address the segmentation of more than two motions. Here, a hierarchical method of initializing the Expectation-Maximization algorithm is described, and it is demonstrated that the Minimum Description Length principle may be used to automatically select the best number of motion layers. The results from over 30 sequences (demonstrating both two and three motions) are presented and discussed.

Algorithms↗
PubMed2006

A system for learning statistical motion patterns.

Analysis of motion patterns is an effective approach for anomaly detection and behavior prediction. Current approaches for the analysis of motion patterns depend on known scenes, where objects move in predefined ways. It is highly desirable to automatically construct object motion patterns which reflect the knowledge of the scene. In this paper, we present a system for automatically learning motion patterns for anomaly detection and behavior prediction based on a proposed algorithm for robustly tracking multiple objects. In the tracking algorithm, foreground pixels are clustered using a fast accurate fuzzy K-means algorithm. Growing and prediction of the cluster centroids of foreground pixels ensure that each cluster centroid is associated with a moving object in the scene. In the algorithm for learning motion patterns, trajectories are clustered hierarchically using spatial and temporal information and then each motion pattern is represented with a chain of Gaussian distributions. Based on the learned statistical motion patterns, statistical methods are used to detect anomalies and predict behaviors. Our system is tested using image sequences acquired, respectively, from a crowded real traffic scene and a model traffic scene. Experimental results show the robustness of the tracking algorithm, the efficiency of the algorithm for learning motion patterns, and the encouraging performance of algorithms for anomaly detection and behavior prediction.

Algorithms↗
PubMed2006

Joint multiregion segmentation and parametric estimation of image motion by basis function representation and level set evolution.

The purpose of this study is to investigate a variational method for joint segmentation and parametric estimation of image motion by basis function representation of motion and level set evolution. The functional contains three terms. One term is of classic regularization to bias the solution toward a segmentation with smooth boundaries. A second term biases the solution toward a segmentation with boundaries which coincide with motion discontinuities, following a description of motion discontinuities by a function of the image spatio-temporal variations. The third term refers to region information and measures conformity of the parametric representation of the motion of each region of segmentation to the image spatio-temporal variations. The components of motion in each region of segmentation are represented as functions in a space generated by a set of basis functions. The coefficients of the motion components considered combinations of the basis functions are the parameters of representation. The necessary conditions for a minimum of the functional, which are derived taking into consideration the dependence of the motion parameters on segmentation, lead to an algorithm which condenses to concurrent curve evolution, implemented via level sets, and estimation of the parameters by least squares within each region of segmentation. The algorithm and its implementation are verified on synthetic and real images using a basis of cosine transforms.

Artificial Intelligence↗
PubMed2003

Motion onset captures attention.

Although visual motion may seem salient, motion per se does not automatically attract attention. We show here, however, that the onset of motion does indeed attract attention. In three experiments, subjects identified target letters in displays that contained targets and distractors. There was no advantage for moving letters among static ones, but there was an advantage for objects that had recently started to move despite the fact that the motion was uninformative. If some additional time was allowed to elapse after motion onset, inhibition of return slowed responding to the item that had started to move-a further sign that the motion onset had captured attention. Finally, detection of target letters was found to be independent of the number of distractors in the display if the target had undergone motion onset, also indicative of attentional capture. We discuss the adaptive significance of sensitivity to onsets in the presence of a relative insensitivity to ongoing motion.

Adult↗
PubMed2004

Direction tuning of human motion detection determined from a population model.

Mass responses that are obtained using electrophysiological or psychophysical techniques are inadequate to characterize motion detectors at the single-unit level. Therefore, we have modelled a population of motion detectors and fitted their mass response to motion-onset EEG data. By examining a single unit of the modelled population we could assess the range of directions and the level of adaptation an individual motion detector responded to. Stimuli were patterns of randomly distributed dots. After subjects had adapted to either a non-moving pattern or to motion in one fixed direction, the pattern moved in one of seven possible test directions. The population model assumed elementary motion detectors with a Gaussian angle-selectivity profile. The population response was calculated as the sum of all adaptation-weighted individual responses to the test direction. In all subjects, we observed sizeable effects of adaptation on test directions close to the adapted direction and small amounts of direction-independent adaptation for all test directions. The model fit explained 75% (Oz) and 94% (lateral derivation) of the total variance and revealed a motion detector bandwidth (full width at half maximum) of 72 degrees (Oz) and 62 degrees (lateral derivation). The maximal adaptation depth was estimated as 72% (Oz) and 66% (lateral derivation). Estimates inferred from the population model representing human motion detectors were found to be close to those obtained by single-cell data from non-human primates.

Electrooculography↗
PubMed2005

Differential involvement of the cerebellum in biological and coherent motion perception.

Perception of biological motion (BM) is a fundamental property of the human visual system. It is as yet unclear which role the cerebellum plays with respect to the perceptual analysis of BM represented as point-light displays. Imaging studies investigating BM perception revealed inconsistent results concerning cerebellar contribution. The present study aimed to explore the role of the cerebellum in the perception of BM by testing the performance of BM perception in patients suffering from circumscribed cerebellar lesions and comparing their performance with an age-matched control group. Perceptual performance was investigated in an experimental task testing the threshold to detect BM masked by scrambled motion and a control task testing the detection of motion direction of coherent motion masked by random noise. Results show clear evidence for a differential contribution of the cerebellum to the perceptual analysis of coherent motion compared with BM. Whereas the ability to detect BM masked by scrambled motion was unaffected in the patient group, their ability to discriminate the direction of coherent motion in random noise was substantially affected. We conclude that intact cerebellar function is not a prerequisite for a preserved ability to detect BM. Because the dorsal motion pathway as well as the ventral form pathway contribute to the visual perception of BM, the question of whether cerebellar dysfunction affecting the dorsal pathway is compensated for by the unaffected ventral pathway or whether perceptual analysis of BM is performed completely without cerebellar contribution remains to be determined.

Adult↗