Motion Detection System Research Articles

Viewing-distance invariance of movement detection.

Since visual movement information is often presented in electronic displays or films it is amazing that there is a paucity of research on the influence of viewing distance on motion detection in cinematograms. We report a relatively high degree of detection constancy with changing viewing distance for coherent motion in random-pixel cinematograms. A constant performance irrespective of viewing-distance is called 'distance-invariance' and for motion detection it proves to hold reasonably well for a relatively wide range of viewing distances both for foveal and eccentric vision. The limits of this viewing-distance invariance are explored as a function of screen velocity. Detection performance is quantified by a threshold signal-to-noise-ratio (SNR-) value, S, which is determined as a function of velocity for a range of viewing distances from 53 to 13,476 mm for foveal vision and from 60 to 1925 mm at 24 degrees eccentricity on the nasal horizontal meridian of the right eye's retina. The data can be explained, at least qualitatively, by a model in which a spatial-resolution stack has a stack of velocity-tuned motion detectors at every resolution layer. Such a 'stack-of-stacks' model is in line with proposals for contrast-detection stack-models, but it suggests that the usual hypothesis that motion perception is based on the activity of two separate systems, the short-range and the long-range system, might be superfluous. This two-systems distinction was largely based on the different performance found for moving random dot patterns and moving form-defined stimuli. A moving random pixel array viewed at very close range (e.g. 6 cm) presents the subject with relatively large almost square 'blobs', which are less dissimilar from the phi-stimuli used in classic motion perception studies than random dot stimuli at the usual medium to large viewing distances. It leads to maximum displacement threshold (Dm-) values that are not untypical of the 'long-range' system, but by gradually increasing the viewing-distance and thus decreasing the pixel-size a continuous change is found from typical long-range to typical short-range values of Dm. The two-systems distinction for motion detection appears to refer to the stimulus rather than to the visual system: The motion-detection system might be forced into a local or a global 'mode of operation' by the choice of stimulus.

Headreader: Realtime motion detection of human head from image sequence

AbstractHuman motion plays a very important role in daily communication. If computers can directly read the meaning of human motion, man‐machine interaction will be improved. This paper presents a three‐dimensional head motion detection system called “headreader.” A simple but very fast algorithm is used which exploits the contrast of hair and face to recognize face orientation. The system extracts the head and face area and then estimates the head motion parameters from the change in position of each area centroids. The head motion is computed at nearly seven frames per second on an SUN4 workstation.

A VLSI architecture for dynamic scene analysis

Analysis of dynamic scenes to obtain motion parameters, structures and identities of the objects present in the scene and/or descriptions of the events taking place in the scene is an important problem in machine vision. Dynamic scene analysis involves processing and analysis of a sequence of image frames (snapshots of the scene) taken at a regularly spaced time interval. Since a large volume of data is to be processed, dynamic scene analysis techniques are, in general, computationally very intensive which makes them unsuitable for applications which require real-time response. A common approach to obtaining motion related information about a scene involves analyzing the characteristics of the connected regions in the corresponding difference pictures. Previous implementations of the difference-picture-based technique use multicomputer and multiprocessor systems which are uneconomical because of the overheads involved. In this paper, we propose a VLSI architecture that exploits the pipelining and the parallelism possible in the above technique. Each processor is organized as a multistage linear pipeline and the processor architecture is simple enough that the motion detection and classification system can be implemented as a single VLSI chip. Once the difference picture has been generated and segmented into separate regions corresponding to motions of different objects, each processor in our proposed chip will independently analyze a different region to classify the type of motion occuring in that region within the scene. Currently, the processor architecture is being laid out in silicon at the University of South Florida for actual fabrication and testing. The chip is expected to operate at the rate of 20 MHz.

Implementation of the template model of vision

Adopting principles learnt from insect vision we have constructed model of a general-purpose front-end visual system for motion detection that is designed to operate in parallel along each photoreceptor axis with only local connections. The model is also designed to assist electrophysiological analysis of visual processing because it puts the response to a moving scene into sets of template responses similar to the distribution of activity among different neurons. An earlier template model divided the visual image into the fields of adjacent receptors, measured as intensity or receptor modulation at small increments of time. As soon as we used this model with natural scenes, however, we found that we had to look at changes in intensity, not intensity itself. Running the new model also generated new insights into the effects of very fast motion, of blurring the image, and the value of lateral inhibition. We also experimented with ways of measuring the angular velocity of the image moving across the eye. The camera eye is moved at a known speed and the range to objects is calculated from the angular velocity of contrasts moving across the receptor array. The original template model is modified so that contrast is saturated in a new representation of the original image data. This reduces the 8-bit grey-scale image to a log, 3 = 1.6-bit image, which becomes the input to a look-up table of templates. The output consists of groups of responding templates in specific ratios that define the input features, and these ratios lead into types of invariance at a higher level of further logic. At any stage, there can be persistent parallel inputs from all earlier stages. This design would enable groups of templates to be tuned to different expected situations, such as different velocities, different directions and different types of edges.

The role of GABA in detecting visual motion

The basic computations underlying the extraction of motion from the visual environment have been characterized in great detail. A non-linear interaction, such as a multiplication, between neighbouring visual elements was shown to be the core of biological motion detectors in different species ranging from insects to man. GABA (γ-aminobutyric acid)-ergic inhibitory synapses suppressing the responses to motion in one direction but not in the other are widely accepted to be the cellular basis for this non-linear interaction. Based on model predictions we can show in combined pharmacological and electrophysiological experiments that in the fly motion detection system GABAergic synapses do not play this role but rather are involved in another important step of motion computation. This makes a reconsideration of the role of inhibition in other motion detection systems necessary.

Computational structure of a biological motion-detection system as revealed by local detector analysis in the fly's nervous system.

The computations performed by individual movement detectors are analyzed by intracellularly recording from an identified direction-selective motion-sensitive interneuron in the fly's brain and by comparing these results with model predictions based on movement detectors of the correlation type. Three main conclusions were drawn with respect to the movement-detection system of the fly: (1) The essential nonlinear interaction between the two movement-detector input channels can be characterized formally by a mathematically almost perfect multiplication process. (2) Even at high contrasts no significant nonlinearities seem to distort the time course of the movement-detector input signals. (3) The movement detectors of the fly are not perfectly antisymmetrical; i.e., they respond with different time courses and amplitudes to motion in their preferred and null directions. As a consequence of this property, the motion detectors can respond to some degree to stationary patterns whose brightness is modulated in time. Moreover, the direction selectivity, i.e., the relative difference of the responses to motion in the preferred and null directions, depends on the contrast and on the spatial-frequency content of the stimulus pattern.

Automatic detection of inter-frame motion in echocardiographic images.

Signal averaging of echocardiographic frames acquired over multiple cardiac cycles has been used to improve image quality. However, misalignment of frames from respiration, transducer or patient movement, and irregular cardiac contraction affects the quality of the resultant averaged image. A motion detection system has been developed using inter-frame subtraction and statistical pattern recognition techniques. Automatic selection of frames exhibiting significant motion in a canine cardiac model compare favorably to manual selection by cardiologists (phi = 0.94) in a test set of 103 images. This method, combined with signal averaging, has resulted in an improvement in image quality.

The nonlinear mechanism of direction selectivity in the fly motion detection system

The nonlinear mechanism of direction selectivity in the fly motion detection system

Ultrasonic motion detection system

First Page

Parallel and serial processes in motion detection.

Apparent motion was used to explore humans' ability to perceive the direction of motion in the visual field. A marked qualitative difference in this ability was found between short- and long-range motion. For short-range motion, the detection of the direction of motion is characterized by parallel operation over a wide visual field (that is, detection performance is independent of the number of objects in an array). When the positional displacement is large relative to an object's size, the direction of motion is detected in a serial manner. The process of detection is limited in this case by the ability to detect other events, such as appearance and disappearance of an object, and the ability to compute their spatio-temporal relations. The results are consistent with a previously suggested division of the motion detection system into short- and long-range processes. The direction of short-range motion can be perceived in parallel (preattentively), whereas long-range motion is attentive and requires more complicated computations. It seems that the detection of long-range motion is a conjunction task, combining the detection of disappearance and appearance.

Facilitatory interactions between flashed lines.

The detectability of pairs of flashed lines was investigated as a joint function of their separation in both space and time. In contrast to previous studies of contrast interactions as a function of either spatial or temporal separation alone, the predominant interaction is not lateral inhibition, but a delayed facilitation. A quantitative model based on probability summation between lateral-inhibitory detectors does not appear able to account for these results. Two related explanations are suggested: either a motion detection system or the nonlinear 'transient' subsystem is being tapped.

The distribution of human motion detector properties in the monocular visual field

The detection of coherent movement in stroboscopically (100 Hz) displayed moving random checkerboard (“Julesz-”) patterns is studied psychophysically for eccentricities up to 48° in the temporal visual field. Starting from the assumption that the studied visual subsystem consists of ensembles of ‘bilocal’ movement detectors (“Reichardt-detectors”), the parameters of these elementary detectors are deduced from the experimental results. This leads to the following interesting insights into the functional architecture of the system. At any eccentricity there is a critical velocity value V c (near the center of the range of detectable velocities) at which both the spans and the delays reach their minimum value. Thus V c can be defined as the ratio of the minimum span to the minimum delay values. At velocities below V c the spans are constant and the delays are inversely proportional to V. At velocities above V c the delays are constant and the spans increase proportional to V. The critical velocity V c at any given eccentricity equals N times V co , where V co , is the critical velocity for foveal vision and N an eccentricity scaling factor. ( N is the inverse normalized “cortical magnification factor”). Thus there is a complete structural invariance in terms of eccentricity-scaled units. Given the eccentricity scaling factor, the determination of two subject dependent constants of foveal vision, the minimum span and minimum delay, suffices to predict the main properties of the motion detection system at any eccentricity.

The low level motion system has both chromatic and luminance inputs

Adaptation to moving isoluminant gratings induces a motion after-effect (MAE). Isoluminant gratings are less effective at inducing and at nulling MAEs than are luminance gratings. These results are consistent with a low-level motion detection system which operates on signals from mechanisms which show both spatial and chromatic opponency.

Spatial and temporal selectivity of the human motion detection system

Measurements were made of spatial frequency, orientation and temporal frequency selectivity of the visual motion system. The results suggest: (1) There exists in the motion system mechanisms selective for spatial frequency. The preferred spatial frequency varies considerably and extends down to at least 0.06 c/deg. (2) At all spatial frequencies (from 0.1 to 10 c/deg) there exist detectors selective for orientation which vary in (directed) orientation tuning to encompass 360°. (3) The bandwidth of both spatial frequency and orientation selectivity vary inversely with spatial frequency: the lower the spatial frequency, the broader the bandwidth. (4) There exist two classes of temporally tuned detectors, one lowpass (sustained) and one bandpass (transient), of preferred temporal frequency of 7–13 Hz (depending on spatial frequency).

Summation of target and mask metacontrast stimuli.

Three experiments are reported; they show the following: (i) Metacontrast occurs at high photopic conditions (250 cd m-2); at this luminance the function peaks at stimulus asynchronies of approximately 40 ms (compared with 100 ms at lower luminances). (ii) The strength of metacontrast is contrast-independent, down to contrast very near detection threshold. (iii) Detection thresholds for the combined target and mask presentation are lower than those for the mask alone, implying summation between target and mask. Summation is greatest at the same asynchronies which yield maximum metacontrast masking. The experiments are taken as evidence in favour of a fusion explanation for metacontrast. An argument is made which implicates temporally units of the motion detection system as being instrumental in the fusion process.

Performance Characteristics of the Annular Core Research Reactor Fuel Motion Detection System

Recent proof tests have shown that the annular core research reactor (ACRR) fuel motion detection system has reached its design goals of providing high temporal and spatial resolution pictures of fuel distributions in the ACRR. The coded aperture imaging system (CAIS) images the fuel by monitoring the fission gamma rays from the fuel that pass through collimators in the reactor core. The gamma-ray beam is modulated by coded apertures before producing a visible light coded image in thin scintillators. Each coded image is then amplified and recorded by an opticalimage-intensifier/fast-framing-camera combination. The proximity to the core and the coded aperture technique provide a high data collection rate and high resolution. Experiments of CAIS at the ACRR conducted under steady-state operation have documented the beneficial effects of changes in the radiation shielding and imaging technique. The spatial resolutions are 1.7 mm perpendicular to the axis of a single liquid-metal fast breeder reactor fuel pin and 9 mm in the axial dimension. Changes in mass of 100 mg in each resolution element can be detected each frame period, which may be from 5 to 100 ms. This diagnostic instrument may help resolve important questions in fuel motion phenomenology.

The structure of the human motion detection system

Unlike technical pattern recognizers, humans are adept at the detection of regions of coherent movements in changing images. Possible physiological mechanisms for this ability are discussed in terms of simple mechanistic models, and the results of psychophysical experiments are presented. These results are compatible with two different mechanistic interpretations. The main result is that the human movement detectors are tuned, and a whole ensemble of mechanisms, tuned to different velocities, reside at any location in the visual field. Thus an observer may easily see two velocity vectors simultaneously at a given place. Segregation occurs when different detectors are stimulated at each side of a border. The spatiotemporal parameters that characterize the units limit the resolution in time and space, whereas sensitivity depends on the number of units that participate in a detection. This number may range between a few (perhaps one) to a thousand or more. Apparently, resolution can be traded against noise immunity. It is argued that technical systems developed on a similar basis might be useful as preprocessors of sequences of images in order to detect features of interest (coherent regions) and to suggest a first rough image segmentation.

Quantitative measurement of body motion using Schottky barrier silicon photodiode.

A new motion detection system has been developed using a laser beam and a Schottky barrier silicon photodiode. The system broadens the scope of gravitational center stabilography by facilitating the quantitative assessment of tremors of body appendages such as the hands and even the head. The system also eliminates cumbersome platforms and wire attachments previously used in gravitational center stabilography. The subject is asked to aim the beam at the photodiode. A quantitative off-center variation parameter, ARDS (Average Radial Distance Squared multiplied by time), was utilized in units of cm2 sec. A preliminary evaluation of the system shows that it is suitable for rapidly screening large numbers of subjects for localised neuromuscular control.

The Landing Response and Visual Processing in the Milkweed Bug, Oncopeltus Fasciatus

ABSTRACT The landing response of the milkweed bug Oncopeltus fasciatus consists primarily of extension at one leg joint (femur-tibia) of each of the front four legs upon presentation of the appropriate visual stimulus. Small-field peripherally directed angular motion in the frontal visual hemisphere is sufficient to elicit the landing response. Movement from the periphery is not an effective stimulus. Response latency to a large-field peripherally moving striped pattern decreases monotonically with increasing angular velocity. This decrease is consistent with what is known of the dynamics of motion-detecting neurones in other insects. It is suggested that motor mechanisms controlling the landing response, opto-motor turning reactions and flight-power behaviour receive inputs from a common neural motion-detection system.