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PubMed2001

Brain areas sensitive to coherent visual motion.

Detection of coherent motion versus noise is widely used as a measure of global visual-motion processing. To localise the human brain mechanisms involved in this performance, functional magnetic resonance imaging (fMRI) was used to compare brain activation during viewing of coherently moving random dots with that during viewing spatially and temporally comparable dynamic noise. Rates of reversal of coherent motion and coherent-motion velocities (5 versus 20 deg s-1) were also compared. Differences in local activation between conditions were analysed by statistical parametric mapping. Greater activation by coherent motion compared to noise was found in V5 and putative V3A, but not in V1. In addition there were foci of activation on the occipital ventral surface, the intraparietal sulcus, and superior temporal sulcus. Thus, coherent-motion information has distinctive effects in a number of extrastriate visual brain areas. The rate of motion reversal showed only weak effects in motion-sensitive areas. V1 was better activated by noise than by coherent motion, possibly reflecting activation of neurons with a wider range of motion selectivities. This activation was at a more anterior location in the comparison of noise with the faster velocity, suggesting that 20 deg s-1 is beyond the velocity range of the V1 representation of central visual field. These results support the use of motion-coherence tests for extrastriate as opposed to V1 function. However, sensitivity to motion coherence is not confined to V5, and may extend beyond the classically defined dorsal stream.

Brain↗
PubMed2001

Functional neuroanatomy of biological motion perception in humans.

We used whole brain functional MRI to investigate the neural network specifically engaged in the recognition of "biological motion" defined by point-lights attached to the major joints and head of a human walker. To examine the specificity of brain regions responsive to biological motion, brain activations obtained during a "walker vs. non-walker" discrimination task were compared with those elicited by two other tasks: (i) non-rigid motion (NRM), involving the discrimination of overall motion direction in the same "point-lights" display, and (ii) face-gender discrimination, involving the discrimination of gender in briefly presented photographs of men and women. Brain activity specific to "biological motion" recognition arose in the lateral cerebellum and in a region in the lateral occipital cortex presumably corresponding to the area KO previously shown to be particularly sensitive to kinetic contours. Additional areas significantly activated during the biological motion recognition task involved both, dorsal and ventral extrastriate cortical regions. In the ventral regions both face-gender discrimination and biological motion recognition elicited activation in the lingual and fusiform gyri and in the Brodmann areas 22 and 38 in superior temporal sulcus (STS). Along the dorsal pathway, both biological motion recognition and non-rigid direction discrimination gave rise to strong responses in several known motion sensitive areas. These included Brodmann areas 19/37, the inferior (Brodmann Area 39), and superior parietal lobule (Brodmann Area 7). Thus, we conjecture that, whereas face (and form) stimuli activate primarily the ventral system and motion stimuli primarily the dorsal system, recognition of biological motion stimuli may activate both systems as well as their confluence in STS. This hypothesis is consistent with our findings in stroke patients, with unilateral brain lesions involving at least one of these areas, who, although correctly reporting the direction of the point-light walker, fail on the biological motion task.

Adult↗
PubMed2005

Deficits of motion integration and segregation in patients with unilateral extrastriate lesions.

Functional neuroimaging in human subjects and single cell recordings in monkeys show that several extra-striate visual areas are activated by visual motion. However, the extent to which different types of motion are processed in different regions remains unclear, although neuropsychological studies of patients with circumscribed lesions hint at regional specialization. We, therefore, studied four patients with unilateral damage to different regions of extrastriate visual cortex on a series of visual discrimination tasks that required them, to a different extent, to integrate local motion signals in order to correctly perceive the direction of global motion. Performance was assessed psychophysically and compared with that of control subjects and with the patients' performance with stimuli presented in the visual field ipsilateral to the lesion. The results indicate considerable regional specialization in extra-striate regions for different aspects of motion processing, namely the largest displacement from frame to frame (D-max) that can sustain perception of coherent motion; perception of relative speed; the amount of coherent motion needed to sustain a percept of global motion in a particular direction; the detection of discontinuities within a moving display; the extraction of form from motion. It was also clear that a defect in local motion, i.e. D-max, can be overcome by integrating local motion signals over a longer period of time. Although no patient suffered from only one defect, the overall pattern of results strongly supports the notion of regional specialization for different aspects of motion processing.

Adult↗
PubMed2002

The neural substrates of biological motion perception: an fMRI study.

We used fMRI to identify the brain areas related to the perception of biological motion (4 T EPI; whole brain). In experiment 1, 10 subjects viewed biological motion (a human figure jumping up and down, composed of 21 dots), alternating with a control stimulus created by applying autoregressive models to the biological motion stimulus (such that the dots' speeds and amplitudes were preserved whereas their linking structure was not). The lengths of the stimulus bouts varied, and therefore the transitions between biological motion and control stimuli were unpredictable. Subjects had to indicate with a button press when each transition occurred. In a related biological motion task, subjects detected short (1 s) disturbances within these displays. We also examined the neural substrates of motion and shape perception, as well as motor imagery, to determine whether or not the cortical regions involved in these processes are also recruited during biological motion perception. Subjects viewed linear motion displays alternating with static dots and a series of common objects alternating with band-limited white noise patterns. Subjects also generated imagery of their own arm movements alternating with visual imagery of common objects. Biological motion specific BOLD signal was found within regions of the lingual gyrus at the cuneus border, showing little overlap with object recognition, linear motion or motion imagery areas. The lingual gyrus activation was replicated in a second experiment that also mapped retinotopic visual areas in three subjects. The results suggest that a region of the lingual gyrus within VP is involved in higher-order processing of motion information.

Adult↗
PubMed2003

Functional MRI studies of human visual motion perception: texture, luminance, attention and after-effects.

Motion of an object is thought to be perceived independently of the object's surface properties. However, theoretical, neuropsychological and psychophysical observations have suggested that motion of textures, called 'second-order motion', may be processed by a separate system from luminance-based, or 'first-order', motion. Functional magnetic resonance imaging (fMRI) responses during passive viewing, attentional modulation and post-adaptation motion after-effects (MAE) of these stimuli were measured in seven retinotopic visual areas (labeled V1, V2, V3, VP, V4v, V3A and LO) and the motion-sensitive area MT/MST (V5). In all visual areas, responses were strikingly similar to motion of first- and second-order stimuli. These results differ from a prior investigation, because here the motion-specific responses were isolated. Directing attention towards and away from the motion elicited equivalent response modulation for the two types. Dramatic post-adaptation (MAE) differences in perception of the two stimuli were observed and fMRI activation mimicked perceptual changes, but did not reveal the processing differences. In fact, no visual area was found to respond selectively to the motion of second-order stimuli, suggesting that motion perception arises from a unified motion detection system.

Adolescent↗
PubMed2000

Arthroscopic treatment for limitation of motion of the elbow.

This study describes the long-term clinical results and serial changes of postoperative range of motion after arthroscopic treatment for limitation of motion of the elbow. Sixty-three patients with limitation of motion of the elbow were treated with arthroscopic procedures. The total range of motion was 79 degrees before surgery. The range of motion showed a progressive increase until 1 year after surgery (mean, 121 degrees). However, after 1 year, the range of motion showed little additional increase. The range of motion acquired during surgery (mean, 122 degrees) usually was the same range that patients achieved during the rehabilitation period (mean, 122 degrees at an average 42.5 months of followup). Extension improved an average of 21 degrees, and flexion increased an average of 23 degrees. The range of motion showed more improvement in patients whose duration of symptoms was less than 1 year (49 degrees) than in those whose duration of symptoms was longer than 1 year (30 degrees). Patients with posttraumatic stiffness had more marked limitation of extension and decreased total range of motion (73 degrees) than did those with degenerative stiffness (86 degrees) before surgery. However, no significant difference existed in the postoperative total range of motion (posttraumatic stiffness, 123 degrees; and degenerative stiffness, 121 degrees). Based on the authors' experience, 92% of patients obtained significant improvement in range of motion after arthroscopic procedures. The minimally invasive nature of elbow arthroscopy is a reproducible and effective procedure for limitation of motion of the elbow with minimal morbidity.

Adolescent↗
PubMed2001

The role of fenestrations and channels on the transverse motion of a soft contact lens.

PURPOSE: Ineffectual removal of potentially harmful species from the postlens tear film (POLTF) may lead to adverse responses among extended wearers of soft contact lenses. It is apparently important to remove bacteria, cell debris, and metabolic products from the postlens tear film to the outer tear lake; the flushing or dispersion rate of these species is enhanced by increasing fluid movement in the tear film driven by periodic lens motion. The contact lens moves laterally (up-down) and transversally (in-out) due to the action of the eyelid forces during blinking. Viscous drag in the POLTF resists lens motion. Consequently, any design change in the lens that reduces viscous drag increases motion and improves flushing of unwanted species from the POLTF. We investigate quantitatively the effect of channels cut on the back surface of the lens and fenestrations (holes) drilled through the lens on transverse lens motion. METHODS: We model the lens as a curved solid body with a periodic arrangement of channels/holes. The cornea is treated as a flat surface, and the hydrodynamic equations of motion are solved for Newtonian fluid transport in the POLTF assuming lubrication and creeping flow. POLTF pressure profiles, obtained by solving these equations, are integrated to determine the lens settling velocity in the transverse direction for a given amount of applied lid force. Lens settling velocity is then compared with the same velocity in the absence of channels/fenestrations. Further, we calculate the total transverse motion in a blink for lenses with and without channels/fenestrations to estimate the possible enhancement in transverse motion due to the channels/fenestrations. RESULTS: Variables that affect the fluid mixing in the POLTF are the postlens tear film thickness, lens thickness, channel length, depth and spacing, and the hole diameter, location, and spacing. We study the effect of each of these variables on the enhancement of transverse motion for channels and holes of diameters varying from 0.1 to 2 mm with spacing varying from 1 to 5 mm. CONCLUSIONS: We demonstrate that incorporation of channels and holes reduces viscous resistance and increases transverse lens motion, and thus increases fluid mixing and dispersive flushing from the POLTF. The increase in transverse motion depends strongly on the postlens tear film thickness. Enhancement of the transverse motion varies from a factor of about 2 to 20 depending on the particular lens design and the postlens tear film thickness. Because fluid mixing increases up to the square of the transverse motion, channels/holes are expected to render flushing of the POLTF considerably more effective. We find that channels and/or fenestrations, when appropriately designed, can provide significant improvement in flushing from the POLTF. This work provides a new quantitative tool for the efficient design of channels/holes in soft contact lenses.

Biomechanical Phenomena↗
PubMed1995

The classification of anatomic- and symptom-based low back disorders using motion measure models.

STUDY DESIGN: This study observed the trunk angular motion features of healthy subjects and those experiencing chronic low back disorders as they flexed and extended their trunks in five symmetric and asymmetric planes of motion. Trunk angular position, velocity, and acceleration were evaluated during several cycles of motion. OBJECTIVE: The trunk angular motion features of the low back disorder group were normalized relative to the healthy subjects and used to 1) evaluate the repeatability and reliability of trunk motion as a measure of trunk musculoskeletal status, 2) quantify the extent of the disorder, 3) determine the extent to which trunk motion measures might be used as quantifiable means to help classify low back disorders. SUMMARY OF BACKGROUND DATA: Given the magnitude of the low back disorder problem, it is problematic that there are few quantitative methods for objectively documenting the extent of a disorder. Impairment ratings of low back disorders can vary by as much as 70% using current systems. Diagnoses and classification schemes are rarely based upon quantitative indicators and we are unable to easily assess and diagnose low back disorders. It is important to quantitatively evaluate low back disorders so that proper treatment can be administered and the risk of exacerbating the problem can be minimized. METHODS: Three-hundred-thirty-nine men and women between 20 and 70 years old who had not experienced significant back pain were recruited as the healthy subjects in this study. One hundred-seventy-one patients with various chronic low back disorders also were recruited and compared with the healthy group of subjects. All subjects wore a triaxial goniometer on their trunks that documented the angular position, velocity, and acceleration of the trunk as the subjects flexed and extended their trunks in each of five planes of motion. Trunk motion features first were normalized for subject gender and age. Several two-stage eight-variable models that account for trunk motion interactions were developed to classify the 510 healthy and low back injured subjects into one of 10 anatomic and symptom-based low back disorder classification categories. RESULTS: Using conservative cross-validation measures, it was found that the stage one eight-variable model could correctly classify more than 94% of the subjects as either healthy or having a low back disorder. One of the stage two eight-variable models was able to reasonably classify the patients with low back disorders into one of 10 low back disorder classification groups. CONCLUSION: The motion-related parameters may relate to biomechanical or learned sensitivities to spinal loading. This study suggests that higher-order trunk motion characteristics hold great promise as a quantitative indicator of the trunk's musculoskeletal status and may be used as a measure of the extent of a disorder and as a measure of rehabilitative progress. Furthermore, once the interactive nature of these trunk motion characteristics is considered, the model could help diagnose low back disorders. However, independent data sets are needed to validate these findings.

Adult↗
PubMed1997

A dynamic approach to spinal instability. Part II: Hesitation and giving-way during interspinal motion.

STUDY DESIGN: Human lumbar functional spinal units (FSUs) were moved throughout their range of motion in sagittal and lateral bending, while the dynamics of this movement were computed in vitro. Functional spinal units were tested intact and after subsequent discectomy and unilateral facetectomy. OBJECTIVE: To determine whether the patterns of small jerks observed during intersegmental motion are sensitive to spinal instability. SUMMARY OF BACKGROUND DATA: Small jerks have been observed as hesitation during increasing velocity and as giving way during decreasing velocity in the experiments described in Part I of this study. METHODS: Human lumbar functional spinal units were moved from extension to flexion, flexion to extension, left to right, and right to left, by a pure moment. Range of motion and velocity and acceleration patterns of the main and coupled motions were evaluated in six degrees of freedom by position changes of attached infrared light-emitting diodes recorded by cameras. Functional spinal units were tested in three surgical conditions (intact, discectomy, and unilateral facetectomy) under two preload conditions (no preload and 400-N preload). Discontinuous accelerations and decelerations (jerks) were computed in these motions and their location in relation to the main angular motion determined. RESULTS: Jerks were observed in almost all motions, in the intact functional spinal units and after surgery. The parameters describing the magnitude of the jerk decreased with increasing component instability. In the sagittal plane, there was a surgical condition by motion direction interaction (P < 0.014) regarding the location of the jerk. Independent from the motion direction, the jerk occurred around the neutral position (in relation to the primary angular motion) in the intact functional spinal units, whereas it shifted from the neutral position toward the beginning of the motion with increasing component instability. CONCLUSION: The results suggest that a small jerk is a normal component of fast intersegmental motion. The jerk has a certain magnitude and location in an intact functional spinal unit, whereas both of the parameters describing the jerk are sensitive to component instability.

Acceleration↗
PubMed2002

Prospective evaluation of trunk range of motion in adolescents with idiopathic scoliosis undergoing spinal fusion surgery.

STUDY DESIGN: Prospective evaluation of spinal range of motion in patients with adolescent idiopathic scoliosis undergoing a spinal fusion. OBJECTIVE: Evaluate changes in triplanar spine range of motion following spinal fusion. SUMMARY AND BACKGROUND DATA: Preoperative and postoperative radiographs have been the major form of outcome analysis of adolescent idiopathic scoliosis fusions. Although the radiographs document static positions of the skeletal system, they do not document dynamic changes. METHODS: Thirty patients with adolescent idiopathic scoliosis undergoing an instrumented spinal fusion underwent triplanar range of motion tests before surgery and at 12 and 24 months after surgery. Videography with reflective surface markers was used to capture the motions. A fused region, unfused regions above and below the fusion, and a global spinal measure were used to assess changes. RESULTS: Results indicated a loss of motion in the coronal and sagittal planes for the fused and unfused spinal regions and a loss of motion in the coronal, sagittal, and transverse planes for the global measurements. Results also indicated preoperative and continued postoperative right and left lateral flexion asymmetries. No significant correlations were found between the total fused levels and changes in range of motion. No significant correlations were found between the lowest instrumented vertebra and changes in range of motion. CONCLUSIONS: Whereas range of motion was reduced in the fused regions of the spine, it was also reduced in unfused regions. The lack of compensatory increase in motion at unfused regions contradicts current theory and suggests early postoperative range of motion therapy to facilitate motion in unfused regions.

Adolescent↗
PubMed2002

Three-dimensional motion patterns during active bending in patients with chronic low back pain.

STUDY DESIGN: The three-dimensional motion patterns of chronic low back pain (LBP) patients were studied during active motions. OBJECTIVE: To evaluate whether the motion patterns of coupling and asymmetry in chronic LBP patients differ from those in the normal population according to previous literature. SUMMARY OF BACKGROUND DATA: There exists little data that correlates vertebral motion with LBP symptoms despite extensive research. Several studies have suggested that patterns of motion are sensitive indicators of spinal pathology, including coupled motion patterns and asymmetry of motion. METHODS: In this study, 34 chronic LBP patients enrolled for an external fixation test performed active bending maneuvers, during which the three-dimensional intervertebral motions were measured continuously with an optoelectronic camera via markers attached to the percutaneous transpedicular screws. If a solid connection between each marker carrier and vertebrae was verified, the three-dimensional rotations of the vertebrae were analyzed with special reference to motion asymmetries and patterns of coupled motion. All data were compared to the normal values in the literature since the methodology is not possible in asymptomatic control subjects. RESULTS: Seven patients were removed from the analysis because of a loose screw-bone interface. In the remaining patients, three distinct patterns of motion were observed in each direction of movement. Significant differences in the extension-flexion ratio, the lateral bending asymmetry, and the coupled axial rotation-lateral bending ratio were found between the chronic LBP group and the normal literature values. CONCLUSIONS: Chronic LBP patients exhibited motion patterns altered from those of the normal population. Specific differences were observed in coupled axial rotation during lateral bending movement, in the symmetry between flexion and extension, and in the symmetry be tween right and left lateral bending.

Adult↗
PubMed2003

Vestibular testing abnormalities in individuals with motion sickness.

HYPOTHESIS: The goal of this study was to compare the results of vestibular testing in individuals with motion sickness to a group of control subjects. BACKGROUND: Studying motion sickness is difficult, because no animal model has been developed and symptoms rarely occur outside motion environments. Tests that can be performed in normal laboratory settings, which help to identify individuals with motion sickness, may be valuable in characterizing this disorder. METHODS: Twenty active duty military individuals with well-documented motion sickness were tested. The test battery included sinusoidal rotational chair testing to calculate vestibulo-ocular reflex function, step-velocity testing to calculate vestibular time constants, and posturography testing to assess vestibulo-spinal reflex status. The results of this test battery were compared with a set of age- and sex-matched controls without motion sickness. RESULTS: Vestibular test abnormalities were demonstrated in individuals with motion sickness. Vestibulo-spinal reflex function on posturography was normal in the control group but abnormal in 70% of the individuals with motion sickness. In addition, 5% of the control group demonstrated a minimal shortening of the absolute time constant, whereas 60% of the individuals with motion sickness had abnormal absolute time constants. CONCLUSION: A significant percentage of individuals with motion sickness demonstrate abnormalities in their time constant or vestibulo-spinal reflex function. These abnormalities can be detected using standard, land-based vestibular tests. These preliminary results have implications in understanding the etiology of motion sickness and may provide outcome measures to be used in treating motion sickness.

Adult↗
PubMed2004

Sources of normal and anomalous motion in retinoscopy.

PURPOSE: Besides the classic "with," "against," and "neutral" absence of motion, retinoscopic reflexes can display anomalous "with" motion in myopia. A model is presented that explains the source of this anomalous motion, as well as quantifies the appearance of retinoscopic motion in myopia and hyperopia. METHODS: Various 2 x 2 matrices were created to describe schematic eyes for a +20 D trial lens, a Gullstrand #1 schematic eye, and an infant schematic eye. Rays from the retinoscope were traced paraxially through these matrices over a full transit of the retinoscope beam across the pupil. Retinal position of the edge of the reflex visible to the observer was plotted as a function of pupil sizes from 2 mm to 16 mm for -5.00 D and +2.00 D refractive errors for the +20 D trial lens. RESULTS: The edge of the retinoscopic reflex could be formed by one of two sources: the edge of the retinoscope beam itself, or the shadow cast by the beam against the edge of the pupil. Anomalous "with" motion arose in myopia when the edge of the reflex was formed by the edge of the beam. The edge of the beam was also visible in hyperopia but did not create anomalous motion. The retinoscope peephole was not involved in the formation of the edge of the reflex. The degree of anomalous motion increased with greater myopia and pupil size. Measured pupil sizes needed to completely eliminate anomalous motion agreed well with those predicted by the model, except at the largest pupil sizes. The limit for anomalous motion depended only on pupil size, refractive error, and working distance but not on whether the system matrix represented the trial lens, a Gullstrand #1 eye, or an infant eye. CONCLUSIONS: Seeing the edge of the beam at large pupil sizes during retinoscopy creates anomalous "with" motion in myopia but may make the reflex easier to see in hyperopia. Anomalous "with" motion in myopia can be managed by adjustment of pupil size, working distance, or net corrected refractive error. Aside from possible effects of aberrations, retinoscopic motion appears to be consistent across various paraxial optical systems for a given refractive error and pupil size.

Artifacts↗
PubMed2006

Electrocardiogram-independent image reconstruction in cardiac multidetector computed tomography using retrospective motion synchronization.

OBJECTIVE: We sought to evaluate an electrocardiogram (ECG)-independent image reconstruction technique for coronary computed tomography (CT)-angiography based on cardiac motion. MATERIALS AND METHODS: The raw data from 20 patients was reconstructed with both an ECG-gated algorithm and a motion-dependent algorithm that calculates the cardiac motion-function directly from the CT raw data using a center of mass technique. Images were reconstructed in 5% steps over the R-R interval and the cardiac motion-cycle. For both approaches multiplanar reformations were created and the set of images with the least motion artifacts was used for the evaluation. Motion artifacts affecting the ascending aorta, the left main coronary artery and the entire course of the LAD, LCX and RCA were scored using a 5-point scale. RESULTS: The mean optimal reconstruction window was at 60% of the R-R interval and 30% of the cardiac motion cycle. A total of 73 of 100 vascular regions showed no motion artifacts in ECG-gated images, with the motion-synchronized algorithm only 41 regions were free of motion artifacts. The mean motion-score was 1.4 (+/-0.6) and 2.4 (+/-1.2) respectively (P < 0.05). CONCLUSION: In the currently implemented form the motion-gated algorithm is inferior to ECG-gated image reconstruction but can be used in patients with an incomplete or corrupt ECG-signal.

Algorithms↗
PubMed1997

Automatic correction of motion artifacts in magnetic resonance images using an entropy focus criterion.

We present the use of an entropy focus criterion to enable automatic focusing of motion corrupted magnetic resonance images. We demonstrate the principle using illustrative examples from cooperative volunteers. Our technique can determine unknown patient motion or use knowledge of motion from other measures as a starting estimate. The motion estimate is used to compensate the acquired data and is iteratively refined using the image entropy. Entropy focuses the whole image principally by favoring the removal of motion induced ghosts and blurring from otherwise dark regions of the image. Using only the image data, and no special hardware or pulse sequences, we demonstrate correction for arbitrary rigid-body translational motion in the imaging plane and for a single rotation. Extension to three-dimensional (3-D) and more general motion should be possible. The algorithm is able to determine volunteer motion well. The mean absolute deviation between algorithm and navigator-echo-determined motion is comparable to the displacement step size used in the algorithm. Local deviations from the recorded motion or navigator-determined motion are explained and we indicate how enhanced focus criteria may be derived. In all cases we were able to compensate images for patient motion, reducing blurring and ghosting.

Artifacts↗
PubMed1994

Influence of stimulus level on acoustic motion-direction sensitivity in barn owl midbrain neurons.

1. Many neurons in the owl's midbrain are able to discriminate by their responses the motion of an acoustic source in one direction, the preferred direction, from the motion of the source in the opposite direction, the null direction. This differential response can be understood by the action of an acoustic motion detector. However, the motion detector would work in an effective way only if the motion direction-sensitive responses of a cell were largely independent of stimulus level. 2. We investigated the level dependence of acoustic motion sensitivity in midbrain neurons with standard extracellular recording techniques. We used an apparent motion paradigm with sounds moving clockwise or counterclockwise in the horizontal plane or stationary sounds for stimulation from free-field speakers. In most cases we added a constant level of background noise to the stimuli having a variable level. Thus we could analyze the responses as a function of the signal-to-noise ratio. 3. Moving and stationary sounds yielded similar response thresholds and similar dynamic ranges. 4. When the background level was changed the response threshold changed accordingly, so that the response threshold always occurred at a constant signal-to-noise ratio independent of background level. 5. The preferred direction of all cells was independent of stimulus level and some 22 percent of the cells showed a directional bias of their response at threshold. In no cell was a change in the preferred direction observed when stimulus level was varied. Typically, however, the motion direction sensitivity, measured by a signed directionality index, was not maximal at threshold. However, the dynamic range, i.e., the range of stimulus levels over which motion direction sensitivity changed, was < or = 20 dB in most cases. Therefore these cells are indeed able to encode motion direction largely independently of stimulus level. 6. We discuss the data within the framework of the acoustic motion detector mentioned above and with respect to earlier reports on acoustic motion sensitivity in the owl and other animals.

Animals↗
PubMed1994

Temporal properties of visual motion signals for the initiation of smooth pursuit eye movements in monkeys.

1. Our goal was to assess whether visual motion signals related to changes in image velocity contribute to pursuit eye movements. We recorded the smooth eye movements evoked by ramp target motion at constant speed. In two different kinds of stimuli, the onset of target motion provided either an abrupt, step change in target velocity or a smooth target acceleration that lasted 125 ms followed by prolonged target motion at constant velocity. We measured the eye acceleration in the first 100 ms of pursuit. Because of the 100-ms latency from the onset of visual stimuli to the onset of smooth eye movement, the eye acceleration in this 100-ms interval provides an estimate of the open-loop response of the visuomotor pathways that drive pursuit. 2. For steps of target velocity, eye acceleration in the first 100 ms of pursuit depended on the "motion onset delay," defined as the interval between the appearance of the target and the onset of motion. If the motion onset delay was > 100 ms, then the initial eye movement consisted of separable early and late phases of eye acceleration. The early phase dominated eye acceleration in the interval from 0 to 40 ms after pursuit onset and was relatively insensitive to image speed. The late phase dominated eye acceleration in the interval 40-100 ms after the onset of pursuit and had an amplitude that was proportional to image speed. If there was no delay between the appearance of the target and the onset of its motion, then the early component was not seen, and eye acceleration was related to target speed throughout the first 100 ms of pursuit. 3. For step changes of target velocity, the relationship between eye acceleration in the first 40 ms of pursuit and target velocity saturated at target speeds > 10 degrees /s. In contrast, the relationship was nearly linear when eye acceleration was measured in the interval 40-100 ms after the onset of pursuit. We suggest that the first 40 ms of pursuit are driven by a transient visual motion input that is related to the onset of target motion (motion onset transient component) and that the next 60 ms are driven by a sustained visual motion input (image velocity component). 4. When the target accelerated smoothly for 125 ms before moving at constant speed, the initiation of pursuit resembled that evoked by steps of target velocity. However, the latency of pursuit was consistently longer for smooth target accelerations than for steps of target velocity.(ABSTRACT TRUNCATED AT 400 WORDS)

Acceleration↗
PubMed2005

Plasma vasopressin, an etiologic factor of motion sickness in rat and human?

Arginine vasopressin (AVP) is considered as an etiologic hormone in motion sickness. However, the possible role of plasma AVP in motion sickness is still controversial. A number of studies have found a gender difference in susceptibility to motion sickness in humans and experimental animals, with female subjects being more susceptible. However, the existence of a gender difference in the AVP response to motion sickness is not known. This study was designed to verify the assumption that plasma vasopressin plays a role in motion sickness. Changes in plasma vasopressin were observed after motion sickness-inducing rotatory stimuli in both sexes in human subjects and rats receiving or not anti-motion-sickness treatments. Plasma vasopressin levels in motion sickness rats exhibited a decrease after rotation in female, but not in male rats. The vasopressin content of the pituitary increased in both sexes. Plasma vasopressin in rats of both sexes tended to increase after a 15-day adaptive training of rotation, but pituitary vasopressin content was not affected under this condition. In contrast, in human subjects, plasma vasopressin levels increased after rotation in all males, but not in females. When anti-motion-sickness drugs (domperidone 10 mg + flunarizine 5 mg) were administered, plasma vasopressin levels were elevated in both females and males. It is concluded that plasma vasopressin increases after motion sickness-induced stimulation provided subjects have become trained to motion sickness. These results do not support an etiologic role of plasma vasopressin in the genesis of motion sickness.

Adult↗