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PubMed2002

Motion versus position in the perception of head-centred movement.

Abstract. Observers can recover motion with respect to the head during an eye movement by comparing signals encoding retinal motion and the velocity of pursuit. Evidently there is a mismatch between these signals because perceived head-centred motion is not always veridical. One example is the Filehne illusion, in which a stationary object appears to move in the opposite direction to pursuit. Like the motion aftereffect, the phenomenal experience of the Filehne illusion is one in which the stimulus moves but does not seem to go anywhere. This raises problems when measuring the illusion by motion nulling because the more traditional technique confounds perceived motion with changes in perceived position. We devised a new nulling technique using global-motion stimuli that degraded familiar position cues but preserved cues to motion. Stimuli consisted of random-dot patterns comprising signal and noise dots that moved at the same retinal 'base' speed. Noise moved in random directions. In an eye-stationary speed-matching experiment we found noise slowed perceived retinal speed as 'coherence strength' (ie percentage of signal) was reduced. The effect occurred over the two-octave range of base speeds studied and well above direction threshold. When the same stimuli were combined with pursuit, observers were able to null the Filehne illusion by adjusting coherence. A power law relating coherence to retinal base speed fit the data well with a negative exponent. Eye-movement recordings showed that pursuit was quite accurate. We then tested the hypothesis that the stimuli found at the null-points appeared to move at the same retinal speed. Two observers supported the hypothesis, a third partially, and a fourth showed a small linear trend. In addition, the retinal speed found by the traditional Filehne technique was similar to the matches obtained with the global-motion stimuli. The results provide support for the idea that speed is the critical cue in head-centred motion perception.

Eye Movements↗
PubMed2003

Quantification and clinical relevance of head motion during computed tomography.

OBJECTIVE: To quantify the 3-dimensional translation and rotation components of head motion during computed tomography and to analyze the influence of such motion on perceptible artifacts and distortion of volume image data sets. METHODS: Using high-precision optoelectronic motion-capture technology, changes in patient head position during axial CT scanning were registered in 20 cases and 2 phantoms with a spatial relative resolution better than 0.003 cm. Statistical analysis was performed on a base of 6-dimensional measurement-vectors, each with 3 translation and 3 rotation values. Because of the recording frequency of the tracking system, more than 80000 values were included in a statistical analysis. RESULTS: All 20 patients had head motion during the CT scanning, with only 4 of 20 patients showing perceptible motion artifacts. The frequency, the extent, and the direction of the movements did not correlate with either the observations made by the radiologic staff or with the patient's subjective estimation of comfort. Translation movements of the head during CT accounted for a maximum of 0.5 cm and rotations of more than 2 degrees without perceptible motion artifacts. The extent of positional changes of the head was found to correlate with the duration of scanning (Pearson's correlation coefficient: 0.647 for translation shifts, 0.453 for rotation shifts). The mean direction of head motion could be characterized predominantly as a rotation around the longitudinal axis of the body (xy plane) at a significance level of 0.01. CONCLUSION: Computed tomography evaluations of the head performed without rigid fixation suffer a spatial distortion of the volume image data sets, caused by interimage motion. The absence of motion artifacts is not correlated with the absence of motion.

Adolescent↗
PubMed1995

Contribution of listeners' approaching motion to auditory distance perception.

Of the several sources of acoustic information for distance perception, those arising from motion of the listener or sound source have received little attention. This motion-related information (recently called acoustic tau) is described, and experiments evaluating its utilization are presented. Accuracy and consistency at walking to the locations of briefly presented sounds were better when people listened while walking than while standing still. Manipulations of the sound to simulate shorter or longer target distances produced appropriate undershooting but not overshooting. The results indicate that people use motion-related acoustic information about distance to guide their locomotor actions, although they do not take full advantage of this information.

Adult↗
PubMed1984

A counterexample to the rigidity assumption in the visual perception of structure from motion.

It has been proposed that the human visual system prefers perceptions of objects that are rigid or undergo minimum form change. A counterexample is presented in which a rigid two-dimensional figure rotating in the frontal plane is perceived as a distorting three-dimensional shape. It is argued that this perception results from the stimulation of automatic processes for perceiving size change, and that these processes are not subject to a general rigidity assumption.

Depth Perception↗
PubMed1996

Functional anatomy on perception of position and motion in depth.

To investigate the neural substrates for the perception of motion and of position in depth, we examined the changes in regional cerebral blood flow during positional and motion stereopsis in humans by positron emission tomography. During positional stereopsis, the right striate and peristriate cortices (areas V1/V2 and V3) and the inferior parietal lobule were significantly activated. During motion stereopsis, the right striate and peristriate cortices (V1/V2) and the ventrolateral occipital cortex (V5) were significantly activated. These results suggest that brain regions active during stereopsis may be dependent, despite their considerable overlap, on the properties of stereopsis, i.e. positional or motion stereopsis.

Adolescent↗
PubMed1993

Nonlinear combination rules and the perception of visual motion transparency.

Experiments were performed to elucidate the decomposition performed by the human visual system in the segregation of complex motion stimuli into distinct moving surfaces. Subjects were presented with achromatic patterns consisting of four types of elements, generated from two random binary luminance patterns (random-dot checkerboards). The luminance of each of the four region classes was under program control. Animated sequences of such images were produced by displacing each of the two generating patterns in opposite directions on a frame by frame basis. These displays evoke a wide variety of percepts, depending on the programmed luminance values, including motion in a single direction, simultaneous motions of transparent sheets in opposite directions, dynamic noise with no directional component, or any combination of the above percepts. A theory is presented which relates the strengths of these percepts to the amplitudes of the components in the perceptual decomposition. The experiments described measured thresholds for seeing noise or "twinkling" in addition to the multiple motions, with the goal of determining the particular signal transformations preceding motion analysis. The results are consistent with a motion extraction mechanism which operates on a linear representation of the input imagery. These results extend a similar finding due to Anstis and Mather [(1985) Perception, 14, 167-179] and call into question the interpretation of a recent study by Stoner, Allbright and Ramachandran [(1990) Nature (London), 344, 153-155].

Contrast Sensitivity↗
PubMed2002

Visuovestibular perception of self-motion modeled as a dynamic optimization process.

This article describes a computational model for the sensory perception of self-motion, considered as a compromise between sensory information and physical coherence constraints. This compromise is realized by a dynamic optimization process minimizing a set of cost functions. Measure constraints are expressed as quadratic errors between motion estimates and corresponding sensory signals, using internal models of sensor transfer functions. Coherence constraints are expressed as quadratic errors between motion estimates, and their prediction is based on internal models of the physical laws governing the corresponding physical stimuli. This general scheme leads to a straightforward representation of fundamental sensory interactions (fusion of visual and canal rotational inputs, identification of the gravity component from the otolithic input, otolithic contribution to the perception of rotations, and influence of vection on the subjective vertical). The model is tuned and assessed using a range of well-known psychophysical results, including off-vertical axis rotations and centrifuge experiments. The ability of the model to predict and help analyze new situations is illustrated by a study of the vestibular contributions to self-motion perception during automobile driving and during acceleration cueing in driving simulators. The extendable structure of the model allows for further developments and applications, by using other cost functions representing additional sensory interactions.

Acceleration↗
PubMed1978

Thresholds of perception for periodic linear motion.

This paper reviews 18 reports which have investigated the absolute threshold of perception of periodic linear motion. The roles of the otolith, somatosensory, and visual detection mechanisms in determining threshold are discussed. Most threshold data for oscillation at frequencies below 1 Hz reflect otolith and somatosensory detection, and show a falling threshold as the frequency rises. This is in accord with neurophysiological data of otolith and somatosensory function. The data for frequencies above 1 Hz reflect an unknown mix of visual, otolith, and somatosensory influences. These data are too heterogenous to indicate whether threshold rises or falls as the frequency of stimulation increases.

Acceleration↗
PubMed1980

On the contours of apparent motion: a new perspective on visual space-time.

Previous results on the perception of motion indicate that perceived motion paths cannot be explained solely in terms of simple feature-specific analyzers. This is particularly true of apparent (phi) motion. In this paper we develop a dynamic network, with simple filtering and summation properties, which can predict the geometric paths of apparent motion in various spatio-temporal configurations. The network assumptions predict a non-Euclidean metric for the visual space-time of motion perception and we consider the implications of such distortions for various visual displays, including illusions.

Humans↗
PubMed1986

Perception of illusory occlusion in apparent motion.

We began with a random matrix of 8 dots displayed briefly on the CRT screen. The pattern was switched off and replaced by an identical array shifted horizontally and the procedure was repeated in a continuous cycle. One of the dots in the second frame was then masked off by an opaque white piece of cardboard. The dots in the surround continued to oscillate as expected but we found that the single unpaired dot also continued to oscillate behind the occluder even though it has no "partner" in the second frame. We found that the magnitude of this illusion ("entrained motion"); increased as we reduced the distance between the inducing dots and the test dot; was unaffected by increasing the number of inducing dots; was enhanced by using slow speeds of alternation; was reduced considerably if there was no visible occluder and the dot in the second frame was simply deleted; was specific to the distance moved by the inducing dots in the surround; the strongest effect was seen when the distance between the occluder and the unpaired dot was approximately the jump-size of the inducing dots. The results suggest that the motion signal derived from the whole dot cluster or "blob" (low spatial frequencies) is spontaneously attributed to the unpaired dot. However the motion of this dot is more readily accepted by the visual system when an opaque occluder is simultaneously visible.

Eye Movements↗
PubMed1994

The role of the blobs in determining the perception of drifting plaids and their motion aftereffects.

Motion aftereffects (MAEs) can be induced by adaptation to a pair of differently oriented drifting gratings whether the gratings are presented simultaneously, as a coherent plaid, or in alternation. The fact that the former MAEs were generally larger than the latter led to the suggestion that simultaneous adaptation involved higher-level extrastriate processes not involved in the alternating effects. In the past few years evidence has accumulated that the difference is in fact due to a low-level monocular process which can be termed the 'blob-tracking mechanism'. A review is presented of the evidence on MAEs induced by simultaneous and alternating adaptation, the evidence for the monocularity of the blob-tracking mechanism, the data which implicate the blob mechanism in the determination of MAE magnitude, perceived plaid drift direction, and in perceived plaid coherence.

Humans↗
PubMed1996

The perception of an opening from expanding motion.

The ability of humans to detect an opening's 3-D structure from expanding motion was tested. Computer simulations of dotted tunnels were used to generate optical flows typically encountered when one moves through an opening. Experiment 1 qualitatively tested the ability to detect the shape of a tunnel's vertical section. The observers could choose the correct shape for each of seven simulated shapes. The percentages of correct responses were much higher than those under static conditions. Experiment 2 tested whether or not one could quantitatively detect the vertical-horizontal proportion of the elliptic tunnels. The results shows quite high correlations (r = .93-.97) between perceived proportions and simulated ones. The slopes of the regression lines were around 1.0. Experiment 3 investigated the necessary stimulus duration for detecting an opening's shape. Relative size (width and height) was significantly detected under four-frame (72.7-msec) conditions by 3 out of 4 subjects. The other subject performed well under eight-frame conditions. These results indicate that the human visual system can instantly detect the 3-D structure of an opening surrounded by objects from expanding optical flows while one is in forward motion.

Computer Simulation↗
PubMed1992

The perception of globally coherent motion.

How do human observers perceive a coherent pattern of motion from a disparate set of local motion measures? Our research has examined how ambiguous motion signals along straight contours are spatially integrated to obtain a globally coherent perception of motion. Observers viewed displays containing a large number of apertures, with each aperture containing one or more contours whose orientations and velocities could be independently specified. The total pattern of the contour trajectories across the individual apertures was manipulated to produce globally coherent motions, such as rotations, expansions, or translations. For displays containing only straight contours extending to the circumferences of the apertures, observers' reports of global motion direction were biased whenever the sampling of contour orientations was asymmetric relative to the direction of motion. Performance was improved by the presence of identifiable features, such as line ends or crossings, whose trajectories could be tracked over time. The reports of our observers were consistent with a pooling process involving a vector average of measures of the component of velocity normal to contour orientation, rather than with the predictions of the intersection-of-constraints analysis in velocity space.

Form Perception↗
PubMed2003

Eye movements provide the extra-retinal signal required for the perception of depth from motion parallax.

It has been unclear whether the perception of depth from motion parallax is an entirely visual process or whether it requires extra-retinal information such as head movements, vestibular activation, or eye movements. Using a motion aftereffect and static test stimulus technique to eliminate visual cues to depth, this psychophysical study demonstrates that the visual system employs a slow eye movement signal, optokinetic response (OKR) in particular, for the unambiguous perception of depth from motion parallax. A vestibular signal, or vestibularly driven eye movement signal is insufficient for unambiguous depth from motion parallax. Removal of the OKR eye movement signal gives rise to ambiguous perceived depth in motion parallax conditions. Neurophysiological studies suggest a possible neural mechanism in medial temporal and medial superior temporal cortical neurons that are selective to depth, motion, and direction of eye movement.

Depth Perception↗
PubMed1983

The effect of two-dimensional and three-dimensional distance on apparent motion.

The problem of how the visual system matches corresponding inputs from one instant to the next to produce the perception of motion has been experimentally examined. The specific concern was whether this correspondence problem is solved prior to the interpretation of three-dimensional distance. Observers judged the degree of apparent motion between pairs of lights in a conflicting motion display. Spatial separation of the lights was varied in two and three dimensions in order to assess whether retinal distance, actual depth, or some combination of these provided critical information for correspondence. The results support Ullman's contention that only two-dimensional (retinal) distances are used in establishing correspondence in motion perception.

Depth Perception↗
PubMedDate not supplied

Motion coherence affects human perception and pursuit similarly.

Pursuit and perception both require accurate information about the motion of objects. Recovering the motion of objects by integrating the motion of their components is a difficult visual task. Successful integration produces coherent global object motion, while a failure to integrate leaves the incoherent local motions of the components unlinked. We compared the ability of perception and pursuit to perform motion integration by measuring direction judgments and the concomitant eye-movement responses to line-figure parallelograms moving behind stationary rectangular apertures. The apertures were constructed such that only the line segments corresponding to the parallelogram's sides were visible; thus, recovering global motion required the integration of the local segment motion. We investigated several potential motion-integration rules by using stimuli with different object, vector-average, and line-segment terminator-motion directions. We used an oculometric decision rule to directly compare direction discrimination for pursuit and perception. For visible apertures, the percept was a coherent object, and both the pursuit and perceptual performance were close to the object-motion prediction. For invisible apertures, the percept was incoherently moving segments, and both the pursuit and perceptual performance were close to the terminator-motion prediction. Furthermore, both psychometric and oculometric direction thresholds were much higher for invisible apertures than for visible apertures. We constructed a model in which both perception and pursuit are driven by a shared motion-processing stage, with perception having an additional input from an independent static-processing stage. Model simulations were consistent with our perceptual and oculomotor data. Based on these results, we propose the use of pursuit as an objective and continuous measure of perceptual coherence. Our results support the view that pursuit and perception share a common motion-integration stage, perhaps within areas MT or MST.

Humans↗
PubMed2006

Influences of the perception of self-motion on postural parameters.

We examined how spatial and temporal characteristics of the perception of self-motion, generated by constant velocity visual motion, was reflected in orientation of the head and whole body of young adults standing in a CAVE, a virtual environment that presents wide field of view stereo images with context and texture. Center of pressure responses from a force plate and perception of self-motion through orientation of a hand-held wand were recorded. The influence of the perception of self-motion on postural kinematics differed depending upon the plane and complexity of visual motion. Postural behaviors generated through the perception of self-motion appeared to contain a confluence of the cortically integrated visual and vestibular signals and of other somatosensory inputs. This would suggest that spatial representation during motion in the environment is modified by both ascending and descending controls. We infer from these data that motion of the visual surround can be used as a therapeutic tool to influence posture and spatial orientation, particularly in more visually sensitive individuals following central nervous system (CNS) impairment.

Adult↗