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PubMed2006

Contributions of the inside and outside leg to maintenance of curvilinear motion on a natural turf surface.

Little is understood of the mechanisms of locomotion if human subjects are not moving in a straight path. The identification of contributory variables to curved motion would also underpin other non-linear actions such as cutting and turning. The performance of such tasks has relevance to both success in sports and exercise, and accident avoidance in an occupational setting. Comparison of ground reaction force values in successive footstrikes would allow an understanding of the contribution of each limb's movement to motion in a curved path. For ecological validity to field games, two natural-turf covered force platforms were located outdoors in a field. Six males (age 25+/-4.73 years; mass 79.7+/-7.17 kg) wearing standard six-stud soccer boots performed straight and curved trials (radius 5m) at velocities of 4.5 and 5.5 ms(-1). Ground reaction force measures were collected on successive footstrikes at 500 Hz, whilst kinematics of the lower extremity were measured at 50 Hz. Results for two successive footfalls showed greater average total force in straight motion (3.53BW versus 3.08BW), with the outside leg contributing most to the movement pattern in curvilinear motion. Ballistic airtime was reduced from straight to curvilinear motion, creating a greater proportional foot contact time during curved running. This, with lowered total force values, suggested a lower centre of gravity during curved motion to minimise drift towards the tangent of the curve. In curved motion, all vertical force measures were greater for the outside leg, with anterior-posterior forces showing the outside leg provided greater propulsion forces and impulse. Improvement in performance in curvilinear motion should therefore be focused at the outside limb.

Adult↗
PubMed2005

Optimizing independent finger flexion with zone V flexor repairs using the Massachusetts General Hospital flexor tenorrhaphy and early protected active motion.

PURPOSE: Independent FDS action has been cited to be problematic with repair of multiple tendons in zone V owing to adhesion formation between the flexor digitorum superficialis (FDS) and the flexor digitorum profundus (FDP) tendons. Of the several described flexor repair techniques the ideal tendon repair should be strong enough to allow for early active motion to minimize adhesion formation and maximize tendon healing. Biomechanical studies have proven the Massachusetts General Hospital (MGH) repair to be strong enough to allow for early active motion. The purpose of this study was to examine the use of the MGH technique for zone V flexor tendon injuries to allow for early protected active motion to achieve independent finger flexion through better differential gliding of the tendons. METHODS: We performed a retrospective review 168 zone V finger flexor tendon repairs for 29 patients performed consecutively over 4 years when early active motion was not contraindicated. The same early protected active motion protocol was used for all of these patients. We reviewed total active motion, independent flexion, rupture, and need for tenolysis. These injuries involved 103 FDS and 65 FDP tendons to 103 fingers. The median follow-up period was 24 weeks. Of these 29 patients 19 were men and 10 were women. The average patient age was 28 years. RESULTS: The total active motion for these zone V repairs was 236 degrees +/- 5 degrees Overall 97 of 103 digits attained good to excellent function and 88 of 103 developed some differential glide. One of these patients required a tenolysis. Three repairs ruptured in 1 patient owing to suture breakage that was associated with noncompliance with the dorsal extension block splint. CONCLUSIONS: Our retrospective review of 168 consecutive flexor tendon repairs showed that the MGH technique allowed for early protected active motion, which provided good to excellent functional outcomes with 88 of 103 developing independent finger flexion at an acceptably low complication risk.

Adult↗
PubMed2005

13C NMR relaxation studies of RNA base and ribose nuclei reveal a complex pattern of motions in the RNA binding site for human U1A protein.

The widespread importance of induced fit and order-disorder transition in RNA recognition by proteins and small molecules makes it imperative that RNA motional properties are characterized quantitatively. Until now, however, very few studies have been dedicated to the systematic characterization of RNA motion and to their changes upon protein or small-molecule binding. The U1A protein-RNA complexes provide some of the best-studied examples of the role of RNA motional changes upon protein binding. Here, we report (13)C NMR relaxation studies of base and ribose dynamics for the RNA internal loop target of human U1A protein located within the 3'-untranslated region (3'-UTR) of the mRNA coding for U1A itself. We also report the semi-quantitative analysis of both fast (nano- to picosecond) and intermediate (micro- to millisecond) motions for this paradigmatic RNA system. We measure (13)C T(1), T(1rho) and heteronuclear nuclear Overhauser effects (NOEs) for sugar and base nuclei, as well as the power dependence of T(1rho) at 500 MHz and 750 MHz, and analyze these results using the model-free formalism. The results provide a much clearer picture of the type of motions experienced by this RNA in the absence of the protein than was provided by the analysis of the structure based solely on NOEs and scalar couplings. They define a model where the RNA internal loop region "breathes" on a micro- to millisecond timescale with respect to the double-helical regions. Superimposed on this slower motion, the residues at the very tip of the loop undergo faster (nano- to picosecond) motions. We hypothesize that these motions allow the RNA to sample multiple conformations so that the protein can select a structure within the ensemble that optimizes intermolecular contacts.

Base Sequence↗
PubMed2005

The human brain's algorithm for extrapolating motion, and its possible gender-dependence.

Some athletes accomplish feats requiring a timing accuracy 100 times better than their reaction time. This capability implies that the brain can accurately extrapolate the motion of objects. We hypothesize that the brain uses a simple algorithm to accomplish this extrapolation, and that the algorithm is influenced by the subject's gender and recent observations of motion. We describe an experiment in timing the motion of a dot across a computer screen designed to discover the motion extrapolation algorithm. Different types of motion of the dot were studied. The experiment was conducted with 126 college students (two-thirds female), who each performed 1000 trials. By using as many as 126,000 trials, the random noise inherent in individual trials averages out, allowing the underlying algorithm to be revealed. The results show that motion extrapolation is done using the average velocity of a moving object with no correction for changes in velocity during the motion, but with an ad hoc adjustment based on recently observed motions and on gender-males having on average a smaller error than females. A future controlled experiment will be needed to establish whether the observed gender difference is due to the greater experience of males with such related tasks as video games and sports.

Algorithms↗
PubMed2005

Nonlinearity of the population activity to transparent motion.

How to represent transparent motion with neuronal populations is important problem for the theory of multiple motion detection. Previous models are based on the assumption that the population activity to transparent motion is proportional to a linear combination of the responses to individual motions. However, there is a possibility that the population activity becomes a nonlinear combination of each motion's component due to the interference, or cross-talk, between two moving patterns. Here we show the model analysis of how a neuronal population represents multiple motions with the spatiotemporal energy model. The model analysis indicates there is a special case that the interference leads to the nonlinearity in the population response, although the linear combination assumption is satisfied in general. This special case corresponds to locally-paired-dot (LPD) stimuli that produce no transparency. Computer simulations show that a simple model for motion detection fails to discriminate two overlapping motions in this case due to the nonlinearity in population responses, and this failure is similar to human perception in LPD stimuli. This result suggests that non-transparency perception in LPD stimuli is naturally explained by the nonlinear property of neuronal responses.

Algorithms↗
PubMed2005

Parallel networks operating across attentional deployment and motion processing: a multi-seed partial least squares fMRI study.

Anticipatory deployment of attention may operate through networks of brain areas that modulate the representations of to-be-attended items in advance of their occurrence through top-down control. Luks and Simpson (2004) (Luks, T.L., Simpson, G.V., 2004. Preparatory deployment of attention to motion activates higher order motion-processing brain regions. NeuroImage 22, 1515-1522) found activations in both control areas and sensory areas during anticipatory deployment of attention to visual motion in the absence of stimuli. In the present follow-up analysis, we tested which network activity during anticipatory deployment of attention is functionally connected with task-related network activity during subsequent selective processing of motion stimuli. Following a cue (anticipatory phase), participants monitored a sequence of complex motion stimuli for a target motion pattern (task phase). We analyzed fMR signal using a partial least squares analysis with previously identified cue- and motion-related voxels as seed regions. The method identified two networks that covaried with the activity of seed regions during the cue and motion-stimulus-processing phases of the task. We suggest that the first network, involving ventral intraparietal sulcus, superior parietal lobule and motor areas, is related to anticipatory and sustained visuomotor attention. Operating in parallel to this visuomotor attention network, there is a second network, involving visual occipital areas, frontal areas as well as angular and supramarginal gyri, that may underlie anticipatory and sustained visual attention processes.

Adult↗
PubMed2004

Dosimetric effect of respiratory motion in external beam radiotherapy of the lung.

BACKGROUND AND PURPOSE: To study the effect of breathing motion on gross tumor volume (GTV) coverage for lung tumors using dose-volume histograms and relevant dosimetric indices. PATIENTS AND METHODS: Treatment plans were chosen for 12 patients treated at our institution for lung carcinoma. GTV volumes of these patients ranged from 1.2 to 97.3 cm(3). A margin of 1-2 cm was used to generate the planning target volume (PTV). Additional margins of 0.6-1.0 cm were added to the PTV when designing treatment portals. For the purposes of TCP calculation, the prescription dose was assumed to be 70 Gy to remove the effects of prescription differences. Setup error was incorporated into the evaluation of treatment plans with a systematic component of sigma(RL) = 0.2 cm, sigma(AP) = 0.2 cm, and sigma(SI) = 0.3 cm and a random component of sigma(RL) = 0.3 cm, sigma(AP) = 0.3 cm, and sigma(SI) = 0.3 cm. Breathing motion was incorporated into these plans based on an independent analysis of fluoroscopic movies of the diaphragm for 7 patients. The systematic component of breathing motion (sigma(RL) = 0.3 cm, sigma(AP) = 0.2 cm, and sigma(SI) = 0.6 cm) was incorporated into the treatment plans on a slice by slice basis. The intrafractional component of breathing motion (sigma(RL) = 0.3 cm, sigma(AP) = 0.2 cm, and sigma(SI) = 0.6 cm) was incorporated by averaging the dose calculation over all displacements of the breathing cycle. Each patient was simulated 500 times to discern the range of possible outcomes. The simulations were repeated for a worst case scenario which used only breathing data with a large diaphragmatic excursion, both with and without intrafractional breathing motion. RESULTS: Dose to 95% of the GTV (D95), volume of the GTV receiving 95% of the prescription dose (V95) and TCP changed an average of -1.4+/-4.2, -1.0+/-3.3, and -1.4+/-3.8%, respectively, with the incorporation of normal breathing effects. In the worst case scenario (heavy breathers), D95 and V95 changed an average of -9.8+/-10.1 and -8.3+/-11.3%, respectively, and TCP changed by -8.1+/-9.1%. GTVs with volumes greater than 60 cm(3) showed stronger sensitivity to breathing especially if the shape was non-ellipsoidal. In the normal breathing case, the probability of a decrease in D95, V95, or TCP of a magnitude greater than 10% is less than 4%, and in the worse case scenario this probability is approximately 30-40% with intrafractional breathing motion included, and less than 10% with intrafractional breathing motion not included. CONCLUSIONS: With the PTV margins routinely used at our center, the effects of normal breathing on coverage are small on the average, with a less than 4% chance of a 10% or greater decrease in D95, V95, or TCP. However, in patients with large respiration-induced motion, the effect can be significant and efforts to identify such patients are important.

Artifacts↗
PubMed2006

A new robotic needle insertion method to minimise attendant prostate motion.

BACKGROUND AND PURPOSE: The purpose of this study is to investigate the efficacy of a new needle insertion method (tapping instead of pushing) in reducing attendant tissue motion. This can be useful in applications where tissue motion due to needle insertion is problematic such as e.g. MRI-guided prostate brachytherapy and breast biopsies. In this study we will focus on prostate motion due to needle insertion. MATERIAL AND METHODS: Prostate motion due to needle insertion was measured in 30 patients, who were transperineally implanted with fiducial gold markers for position verification in prostate intensity modulated radiotherapy. In total 32 needles were manually pushed into the prostate and 29 were tapped with a prototype robotic system. The prostate motion in the cranio-caudal direction was measured on the video record of the ultrasound images. Differences in prostate motion between the two needle insertion methods were analysed making use of SPSS. RESULTS: The mean prostate motion was 5.6mm (range 0.3-21.6) when the needle was pushed and 0.9 mm (range 0-2.0) when the needle was tapped into the prostate (p<0.001). CONCLUSION: Prostate motion was significantly less when the needle was tapped into the prostate compared to when the needle was pushed. This result is important for the development of a tapping, MRI-guided, prostate implant robotic system.

Biopsy↗
PubMed2005

Visual motion integration in schizophrenia patients, their first-degree relatives, and patients with bipolar disorder.

Many schizophrenia patients show degraded detection of coherent motion. This visual deficit may (1) be a consequence of having a specifically schizophrenic psychosis, (2) be a non-specific effect of suffering from a severe illness (i.e., "generalized deficit"), or (3) reflect properties of the visual motion processing system that play an antecedent, possibly causal role in the pathophysiology of a disposition to schizophrenia. To distinguish among these possibilities, we measured the accuracy of detecting the direction of coherent motion in 29 schizophrenia patients, 20 first-degree relatives of schizophrenia patients, 19 patients with bipolar disorder and 33 normal controls. The task requires the integration of dynamic signals from stochastic random dot patterns in order to discern the direction of their motion. Schizophrenia patients, as a group, showed significantly elevated thresholds for detecting the direction of coherent motion, but relatives of schizophrenia patients and patients with bipolar disorder did not differ from normal controls on this task. The results indicate that visual motion integration, normally mediated in motion-sensitive brain areas such as the Middle Temporal Area, is impaired in patients with a clinically manifest schizophrenic psychosis, but is intact in patients with a non-schizophrenic psychosis (bipolar disorder) and in the relatives of schizophrenia patients. Our findings suggest that deficiencies in integrating motion signals, while specific for schizophrenia, do not seem to be a co-familial trait.

Adult↗
PubMed2004

Motion repulsion is monocular.

Motion repulsion is the illusory enlargement of the angle between objects moving in two different directions of motion. Previous work suggests that motion repulsion occurs under dichoptic conditions, and therefore is binocular. In reference repulsion the direction of motion is misperceived even if only a single direction of motion is presented. In an experiment I show that repulsion under dichoptic conditions is correlated with reference repulsion, but not with binocular motion repulsion. This suggests that motion repulsion proper, which occurs over and beyond reference repulsion, does not occur under dichoptic conditions, implying that motion repulsion is monocular.

Humans↗
PubMed2004

Attenuation of perceived motion smear during vergence and pursuit tracking.

When the eyes move, the images of stationary objects sweep across the retina. Despite this motion of the retinal image and the substantial integration of visual signals across time, physically stationary objects typically do not appear to be smeared during eye movements. Previous studies indicated that the extent of perceived motion smear is smaller when a stationary target is presented during pursuit or saccadic eye movements than when comparable motion of the retinal image occurs during steady fixation. In this study, we compared the extent of perceived motion smear for a stationary target during smooth pursuit and vergence eye movements with that for a physically moving target during fixation. For a target duration of 100 ms or longer, perceived motion smear is substantially less when the motion of the retinal image results from vergence or pursuit eye movements than when it results from the motion of a target during fixation. The reduced extent of perceived motion smear during eye movements compared to fixation cannot be accounted for by different spatio-temporal interactions between visual targets or by unequal attention to the moving test spot under these two types of conditions. We attribute the highly similar attenuation of perceived smear during vergence and pursuit to a comparable action of the extra-retinal signals for disjunctive and conjugate eye movements.

Convergence, Ocular↗
PubMed2004

Illusory motion reversal is caused by rivalry, not by perceptual snapshots of the visual field.

In stroboscopic conditions--such as motion pictures--rotating objects may appear to rotate in the reverse direction due to under-sampling (aliasing). A seemingly similar phenomenon occurs in constant sunlight, which has been taken as evidence that the visual system processes discrete "snapshots" of the outside world. But if snapshots are indeed taken of the visual field, then when a rotating drum appears to transiently reverse direction, its mirror image should always appeared to reverse direction simultaneously. Contrary to this hypothesis, we found that when observers watched a rotating drum and its mirror image, almost all illusory motion reversals occurred for only one image at a time. This result indicates that the motion reversal illusion cannot be explained by snapshots of the visual field. The same result is found when the two images are presented within one visual hemifield, further ruling out the possibility that discrete sampling of the visual field occurs separately in each hemisphere. The frequency distribution of illusory reversal durations approximates a gamma distribution, suggesting perceptual rivalry as a better explanation for illusory motion reversal. After adaptation of motion detectors coding for the correct direction, the activity of motion-sensitive neurons coding for motion in the reverse direction may intermittently become dominant and drive the perception of motion.

Humans↗
PubMed2004

Figure-ground segregation can rely on differences in motion direction.

If the elements within a figure move synchronously while those in the surround move at a different time, the figure is easily segregated from the surround and thus perceived. Lee and Blake (1999) [Visual form created solely from temporal structure. Science, 284, 1165-1168] demonstrated that this figure-ground separation may be based not only on time differences between motion onsets, but also on the differences between reversals of motion direction. However, Farid and Adelson (2001) [Synchrony does not promote grouping in temporally structured displays. Nature Neuroscience, 4, 875-876] argued that figure-ground segregation in the motion-reversal experiment might have been based on a contrast artefact and concluded that (a)synchrony as such was 'not responsible for the perception of form in these or earlier displays'. Here, we present experiments that avoid contrast artefacts but still produce figure-ground segregation based on purely temporal cues. Our results show that subjects can segregate figure from ground even though being unable to use motion reversals as such. Subjects detect the figure when either (i) motion stops (leading to contrast artefacts), or (ii) motion directions differ between figure and ground. Segregation requires minimum delays of about 15 ms. We argue that whatever the underlying cues and mechanisms, a second stage beyond motion detection is required to globally compare the outputs of local motion detectors and to segregate figure from ground. Since analogous changes take place in both figure and ground in rapid succession, this second stage has to detect the asynchrony with high temporal precision.

Artifacts↗
PubMed2005

Attenuation of perceived motion smear during the vestibulo-ocular reflex.

Previous studies indicated that less motion smear is perceived when a physically stationary target is presented during voluntary eye movements than when similar retinal-image motion occurs during steady fixation. In this study, we assessed whether the perception of motion smear is attenuated also during the involuntary vestibulo-ocular reflex (VOR). Normal observers matched the length of perceived smear in two experimental conditions that were designed to produce similar trajectories of retinal image motion. In the fixation condition, a small bright target was presented for a duration of 50-200 ms in rightward or leftward motion, while the observer remained stationary and maintained fixation. In the VOR condition, the target moved along with the observer, who underwent full-body rotation around a vertical axis in darkness. Horizontal eye movement recordings during VOR trials allowed us to calculate the velocity of retinal image motion on each VOR trial. The principal result was that the extent of perceived motion smear was significantly less during VOR than fixation trials, particularly for target durations of 100 ms or longer. These findings support the conclusion that extra-retinal signals during the involuntary VOR contribute to a reduction of perceived motion smear.

Analysis of Variance↗
PubMed2005

Selective attention and cyclopean motion processing.

The effect of diverted selective attention on the induction of the cyclopean motion aftereffect (aftereffect induced from dynamic disparity information) was investigated. The luminance motion aftereffect was examined for comparison. During diverted-attention trials, observers ignored background adapting motion and performed a low-load or high-load rapid serial visual presentation (RSVP) task presented in the center of the motion display. Baseline motion aftereffects were obtained with no diverted attention. The results showed that the cyclopean motion aftereffect, similar to the luminance motion aftereffect, declined only modestly under diverted-attention conditions. Selective attention appears to play a modest role in the visual processing of cyclopean motion.

Adaptation, Ocular↗
PubMed2005

An illusory transformation of optic flow fields without local motion interactions.

The focus of expansion (FOE) of a radially expanding optic flow pattern that is overlapped by unidirectional laminar flow is perceptually displaced in the direction of that laminar flow. There is continuing debate on whether this effect is due to local or global motion interactions. Here, we show psychophysically that under conditions without local motion transparency the illusion becomes weaker but can still be observed. In our experiments, the radial and laminar-flow fields were not presented with overlap but separately to the left and right halves of the visual field with a blank vertical strip of 15 degrees horizontal width in between. The illusory shift observed in this condition cannot be explained by local motion interactions because (a) no transparent motion was present in the stimulus, and (b) the receptive fields of cortical cells involved in the analysis of local motion cross the vertical midline of the visual field to a limited extent. We conclude that global motion detectors that integrate motion from both halves of the visual field play a role in shifting the perceived position of the FOE and that local motion interactions may be sufficient, but are not necessary for the optic flow illusion to occur.

Adult↗
PubMed2005

Repetitive TMS over posterior STS disrupts perception of biological motion.

Biological motion perception, the recognition of human action depicted in sparse dot displays, is supported by a network of brain areas including the human posterior superior temporal sulcus (pSTS). We have used repetitive transcranial magnetic stimulation (rTMS) to temporarily disrupt cortical activity within the pSTS and subsequently measured sensitivity to biological motion. Sensitivity was measured for canonical (upright) point-light animations and for animations inverted 180 deg, a manipulation that renders biological motion more difficult to recognize. Observers were markedly less sensitive to upright biological motion following pSTS stimulation. In contrast, performance remained normal for inverted biological motion following pSTS stimulation, and normal for upright and inverted biological motion following stimulation over visual motion sensitive area MT+/V5. In connection with previous brain imaging results, our findings demonstrate that normal functioning of the posterior STS is required for intact perception of biological motion.

Adult↗
PubMed2005

Bistable Glass-pattern motion reveals two different processes.

Examining the two motion processes is an elusive task due to the difficulty of finding a proper stimulus paradigm. A rotational Glass pattern created with a random-dot array by superimposing its rotated version on the top of it can provide such a paradigm. If we displace only its rotated part in the vertical or horizontal direction, a bistable motion occurs; local dot motion in the same direction and Glass-pattern motion in the orthogonal direction. From two experiments, we found local dot motion is predominant in short spatiotemporal range and global pattern motion in long spatiotemporal range. Since the stimulus allows us to maintain all of its properties identical except for the changes in spatiotemporal parameters, this result shows more robustly that the energy-based first-order motion favors short spatiotemporal ranges while the pattern-based second-order motion favors long spatiotemporal ranges.

Humans↗