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At least 271 records · Page 15Linked to original sources
PubMed2001

Motion-surface labeling by orientation, spatial frequency and luminance polarity in 3-D structure-from-motion.

A compelling percept of three-dimensionality is attainable from a purely motion-defined simulation of a transparent rotating cylinder, referred to as 3-D structure-from-motion (SFM). Interestingly, subjects rarely perceive reversals of the cylinder's direction of rotation when they are introduced. Treue, Andersen, Ando, and Hildreth (Vision Res. 35 (1995) 139-148) have argued that this reflects the visual system's insensitivity to the textural detail on the cylinder's motion surfaces. We have recently shown however that with cylinders made from oriented micropatterns, motion reversals are perceived when the orientations of the micropatterns are different on the cylinder's front/back surfaces, suggesting that the visual system is sensitive to the type of feature in these stimuli (Vision Res. 39 (1999) 881-886). In the present study we extended this finding by testing for feature-sensitivity along other dimensions besides orientation, specifically spatial frequency, colour and luminance polarity. We found that subjects perceived more rotation direction reversals when the front/back surfaces of the cylinder were segregated, as opposed to non-segregated by feature-type, along all of these dimensions except, notably, colour. We also investigated the stage at which the feature-sensitivity is incorporated in 3-D SFM. We reasoned that if 3-D SFM mechanisms were tuned, or labeled for feature-type, swapping of features during the cylinder's rotation would result in illusory reversals in just the feature-segregated condition, whereas if grouping of like-features preceded the formation of 3-D motion surfaces, no such illusory reversals would be expected. We found that feature-swapping resulted in more illusory reversals in the feature-segregated compared to non-segregated conditions, supporting the mechanism tuning, or labeling, hypothesis.

Color Perception↗
PubMed1998

Veridical perception of global motion from disparate component motions.

Although it is in principle possible to determine the direction of motion of an object by combining the motion of its one-dimensional oriented contours (Fennema CL, Thompson WB. Comput. Graph. Image Processing 1979;9:301-315) there is still much debate on whether human observers can do so. The Intersection Of Constraint (IOC) rule proposed by Adelson and Movshon (Adelson EH, Movshon JA. Nature 1982;300:523-525), although compatible with the veridical object's motion, was challenged by recent psychophysical data obtained with type II plaids or lines moving behind apertures: perceived direction of motion is biased toward the vectorial average of the component motions, rather than in the direction predicted by the IOC rule. Since the velocity predicted by the vectorial rule is inconsistent with the physical velocity, its use leads to the puzzling prediction that the perceived position of a moving object becomes inconsistent with its actual position. In the present paper, the perceived path of a figure defined by its one-dimensional contours and moving behind apertures along a circular trajectory is compared with the discrepant predictions of the IOC and of the Vectorial model. The results show that the perceived path is close to veridical with these stimuli, therefore challenging the idea that the visual system uses a vector averaging rule.

Depth Perception↗
PubMed2002

Visual motion stimulation, but not visually induced perception of self-motion, biases the perceived direction of verticality.

Large-field torsional optokinetic stimulation is known to affect the perceived direction of gravity with verticality judgements deviating towards the direction of visual stimulus rotation. The present study aimed to replicate this effect and to examine it further by subjecting participants to optokinetic stimulation in roll, resulting in spontaneous alternations between the perception of object-motion and that of contradirectional self-motion (vection), as reported by the subjects. Simultaneously, subjects were oscillated laterally in a flight simulator and indicated their perception of postural verticality. Results confirmed that rotation of the visual environment in the frontal plane biases the perceived orientation of gravity towards the direction of visual stimulus motion. However, no differential effect of perceptual state on postural verticality was obtained when contrasting verticality judgements made during the perception of object-motion with those obtained during reported self-motion perception. This finding is likely to reflect a functional segregation of central nervous visual-vestibular subsystems that process the perception of self-tilt and that of self-rotation to some degree independently.

Adult↗
PubMed2000

Motion vision: are 'speed lines' used in human visual motion?

Motion analysis poses problems for any visual system, not least because of the ambiguities inherent in motion signals. Recent studies suggest that the human motion system may exploit 'motion streaks' - analogous to the cartoonist's speed lines - to help resolve the direction of ambiguous motion.

Humans↗
PubMed1996

Motion transparency arises from perceptual grouping: evidence from luminance and contrast modulation motion displays.

What circumstance lead to the perception of global motion transparency? it has been shown that, in paired random dot displays, motion transparency can be abolished if the separation of the dot pairs is sufficiently small. Motion transparency has also been shown to be influenced by high level cognitive cues. Here, we report that the combination of two moving dot stimuli, which separately invoke a percept of transparent motion, gives rise to a non-transparent percept of local rotation. These stimuli were constructed using various different pattern elements, including luminance defined elements and contrast modulations. The results extend and support the view that high-level grouping of local measures of the velocity field can determine whether a motion transparency is perceived or not.

Humans↗
PubMedDate not supplied

Effect of motion on cardiac SPECT imaging: recognition and motion correction.

Cardiac motion is likely to occur during long single photon emission computed tomography acquisitions or if there is considerable patient discomfort. Motion causes data misregistration and may decrease the accuracy of interpretation of cardiac single photon emission computed tomography by introducing image artifacts, such as smearing of counts around the ventricle ("hurricane sign"), distortion and discontinuities of the ventricular walls, nonanatomic defects, and hot spots. Although motion should be avoided during data acquisition, motion correction techniques have been developed to allow for manual or semiautomated compensation of cardiac displacement and should be used when motion cannot be eliminated.

Heart↗
PubMed1992

Visible persistence is reduced by fixed-trajectory motion but not by random motion.

Despite the sluggish temporal response of the human visual system, moving objects appear clear and without blur, which suggests that visible persistence is reduced when objects move. It has been argued that spatiotemporal proximity alone can account for this modulation of visible persistence and that activation of a motion mechanism per se is not necessary. Experiments are reported which demonstrate that there is a motion-specific influence on visible persistence. Specifically, points moving in constant directions, or fixed trajectories, show less persistence than points moving with the same spatial and temporal displacements but taking random walks, randomly changing direction each frame. Subjects estimated the number of points present in the display for these two types of motion conditions. Under conditions chosen to produce 'good' apparent motion, ie small temporal and spatial increments, the apparent number of points for the fixed-trajectory condition was significantly lower than the apparent number in the random-walk condition. The traditional explanation of the suppression of persistence based on the spatiotemporal proximity of objects cannot account for these results. The enhanced suppression of persistence observed for a target moving in a consistent direction depends upon the activation of a directionally tuned motion mechanism extended over space and time.

Female↗
PubMed1999

Motion parallel to line orientation: disambiguation of motion percepts.

Four experiments demonstrate that lines indicating path of movement can generate rotational percepts in a multistable motion display that usually produces only horizontal or vertical motion percepts. The properties of the path-of-movement lines are predicted by a neural-network theory of visual perception. Experimental results validate the theory's predictions by demonstrating that movement of the display elements seems to follow an increasing luminance gradient in lines but not bars, and that illusory contours have similar effects. Experimental results also demonstrate that, in a choice between movement along lines drawn parallel or orthogonal to possible motion paths, observers more often see movement along the lines parallel to the motion path. These results suggest modifications to current computational and neurophysiological theories of motion perception.

Computer Graphics↗
PubMed2005

Motion parallax driven by head movements: conditions for visual stability, perceived depth, and perceived concomitant motion.

Yoking the movement of the stimulus on the screen to the movement of the head, we examined visual stability and depth perception as a function of head-movement velocity and parallax. In experiment 1, for different head velocities, observers adjusted the parallax to find (a) the depth threshold and (b) the concomitant-motion threshold. Between these thresholds, depth was seen with no perceived motion. In experiment 2, for different head velocities, observers adjusted the parallax to produce the same perceived depth. A slower head movement required a greater parallax to produce the same perceived depth as faster head movements. In experiment 3, observers reported the perceived depth for different parallax magnitudes. Perceived depth covaried with smaller parallax without motion perception, but began to decrease with larger parallax and concomitant motion was seen. Only motion was seen with the larger parallax.

Adult↗
PubMed2005

Depth and motion in historical descriptions of motion parallax.

Motion parallax was described as a cue to depth over 300 years ago and as producing apparent motion over 150 years ago. In recent years, experimental interest in motion parallax has increased, following the rediscovery of the idea that stimulus motion can be yoked to head movement. We compare the historical descriptions with some contemporary research, which indicates how depth and motion perception are dependent on the conditions of stimulation.

Depth Perception↗
PubMed2002

Activity patterns in human motion-sensitive areas depend on the interpretation of global motion.

Numerous imaging studies have contributed to the localization of motion-sensitive areas in the human brain. It is, however, still unclear how these areas contribute to global motion perception. Here, we investigate with functional MRI whether the motion-sensitive area hMT+/V5 is involved in perceptual segmentation and integration of motion signals. Stimuli were overlapping moving gratings that can be perceived either as two independently moving, transparent surfaces or as a single surface moving in an intermediate direction. We examined whether motion-sensitive area hMT+/V5 is involved in mediating the switches between the two percepts. The data show differential activation of hMT+/V5 with perceptual switches, suggesting that these are associated with a reconfiguration of cell assemblies in this area.

Brain↗
PubMed2005

Adaptive prediction of internal target motion using external marker motion: a technical study.

An adaptive prediction approach was developed to infer internal target position by external marker positions. First, a prediction model (or adaptive neural network) is developed to infer target position from its former positions. For both internal target and external marker motion, two networks with the same type are created. Next, a linear model is established to correlate the prediction errors of both neural networks. Based on this, the prediction error of an internal target position can be reconstructed by the linear combination of the prediction errors of the external markers. Finally, the next position of the internal target is estimated by the network and subsequently corrected by the reconstructed prediction error. In a similar way, future positions are inferred as their previous positions are predicted and corrected. This method was examined by clinical data. The results demonstrated that an improvement (10% on average) of correlation between predicted signal and real internal motion was achieved, in comparison with the correlation between external markers and internal target motion. Based on the clinical data (with correlation coefficient 0.75 on average) observed between external marker and internal target motions, a prediction error (23% on average) of internal target position was achieved. The preliminary results indicated that this method is helpful to improve the predictability of internal target motion with the additional information of external marker signals. A consistent correlation between external and internal signals is important for prediction accuracy.

Algorithms↗
PubMed2005

Pattern motion and component motion sensitivity in cat superior colliculus.

Single neurons in the superior colliculus of the cat were tested for their direction-tuning responses to random-line patterns composed of identical short lines moving obliquely to their common orientation. A substantial population of cells responded primarily to the veridical direction of pattern motion while a few were sensitive to the orientation of component lines. Moreover, for most cells, the pattern motion sensitivity decreased when the orientation element was enhanced by elongating the component lines in stimulus. Further analysis found that the initial transient responses after stimulus onset were relatively more sensitive to component motion than the subsequent sustained responses. These findings suggest that the superior colliculus is involved in the higher-order analysis of visual motion so that collicular neurons can signal coherent pattern motion in many cases.

Animals↗
PubMed2000

Response time prolongation for a motion stimulus in patients with glaucoma and its relationship with elevation of the motion threshold.

PURPOSE: To investigate whether response times for a motion stimulus are prolonged in glaucoma and to investigate the relationship between response time prolongation and motion threshold elevation in glaucoma. METHOD: Motion displacement thresholds and response times were measured in 15 patients with glaucoma and 18 age-matched control subjects. RESULTS: Mean test response times were significantly prolonged in the glaucomatous eyes than in the control eyes, with a mean delay of 200 milliseconds. After correcting for threshold elevation, response times at the motion threshold showed no significant difference between the groups. CONCLUSIONS: Response times for motion detection are significantly prolonged in glaucoma and are accounted for by the threshold elevation in patients with glaucoma. The implications of these results are discussed in terms of the use of response time analysis to determine subject reliability.

Adult↗
PubMed2003

A method for incorporating organ motion due to breathing into 3D dose calculations in the liver: sensitivity to variations in motion.

Organ motion has been previously described using a probability distribution function that depends solely upon the amplitude of motion and the degree of asymmetry in the breathing cycle, and that function has been used with patient specific parameters to correct static dose distributions for patient breathing using a dose convolution method. In this study, the consequences of errors in the selection of those two parameters were evaluated. Patients previously treated using a focal liver dose escalation protocol were selected with tumors located in the superior or inferior portion of the liver. For a fixed degree of asymmetry (amplitude), the amplitude (asymmetry) of motion was varied about its nominal value and the consequences of organ motion on the dose distribution and the (potentially new) prescription dose were evaluated. These comparisons show that small (+/- 3 mm) variations of the amplitude of motion about the nominally measured value may not result in clinically significant changes (< a single fraction change in the prescription dose), however, larger variations (> 5 mm) can lead to significant changes. Assuming from measurement that the patient breathes asymmetrically (spends more time at expiration), variations in the assumed degree of asymmetry rarely lead to clinically significant changes; the most significant cause for concern being when the patient breathing cycle is maximally different from the treatment planning case (e.g., patient assumed to spend more time at expiration, but later breaths symmetrically). The results point out where quality assurance efforts should be concentrated to help assure the validity of the assumptions used to correct the static dose distributions for patient breathing using the convolution method.

Algorithms↗
PubMed1981

The relationship of pulmonary valve motion to the motion of surrounding cardiac structures: a two-dimensional and dual M-mode echocardiographic study.

To assess the relationship of late diastolic pulmonary valve motion to motion of adjacent cardiac structures, we performed two-dimensional and dual M-mode echocardiography on 15 pulmonary normotensive (group A) and nine pulmonary hypertensive subjects (group B). Simultaneous pulmonary valve and posterior aortic wall a-waves were less prominent in group B than in group A (p less than 0.001), and their amplitudes were linearly related within each group (r = 0.83). Analysis of two-dimensional studies confirmed a relationship between pulmonary valve and posterior aortic wall late diastolic motion. No subject had independent presystolic motion of the pulmonary valve within the pulmonary artery. Subjects with shallow a-waves had impaired left atrial emptying compared with those with normal a-wave amplitudes (p less than 0.01). We conclude that the pulmonary valve a-wave does not represent independent valvular displacement, but rather, reflects motion of the entire cardiac base. Variations in a-wave morphology may result, at least in part, from the effects of altered ventricular geometry and compliance on left atrial emptying.

Aorta↗
PubMed1999

Motion sickness in public road transport: the relative importance of motion, vision and individual differences.

The relative importance of vehicle motion, a view of the road ahead and passenger characteristics in the causation of motion sickness in road transport has been investigated using survey data from 3256 coach passengers and measurements of coach motion. Overall, 28% of passengers said they felt unwell during coach travel. Prior experience of sickness, travel regularity and age were the factors most highly correlated with illness. Increased vehicle motion and poorer forward vision also correlated with illness. Little difference in illness was apparent with a good view of the road ahead, regardless of motion exposure, although vision alone was not sufficient to eliminate passenger sickness entirely. The results suggest that travel sickness could be significantly reduced by improved forward external vision and that improved forward vision may be particularly beneficial for individuals new to coach travel and for those who travel less often.

Adolescent↗
PubMed1995

Extracting object motion during observer motion: combining constraints from optic flow and binocular disparity.

Detection of object motion by moving observers and perception of velocity by stationary or moving observers ordinarily require information about object distance. It might be expected that object motion could be obtained without distance by use of a combination of optic flow and binocular disparity information. We describe how object motion could, in principle, be derived this way. The analysis also permits recovery of target distance. Finally, information about the observer's motion may be obtained in a similar fashion, assuming the existence of two stationary environmental points at an unknown distance. Although studies of human observers have not been completed, it appears that these informational variables are available under conditions in which observers perform well at detecting motion and stability. In particular, the information may help to explain why a visible surface in near space facilitates accurate perception.

Humans↗