Showing papers on "Monocular vision published in 1988"

Cortical dynamics of three-dimensional form, color, and brightness perception I: Monocular theory

Abstract: A real-time visual processing theory is developed to explain how three-dimensional form, color, and brightness percepts are coherently synthesized. The theory describes how several fundamental uncertainty principles which limit the computation of visual information at individual processing stages are resolved through parallel and hierarchical interactions among several processing stages. The theory hereby provides a unified analysis and many predictions of data about stereopsis, binocular rivalry, hyperacuity, McCollough effect, textural grouping, border distinctness, surface perception, monocular and binocular brightness percepts, filling-in, metacontrast, transparency, figural aftereffects, lateral inhibition within spatial frequency channels, proximity-luminance covariance, tissue contrast, motion segmentation, and illusory figures, as well as about reciprocal interactions among the hypercolumns, blobs, and stripes of cortical areas VI, V2, and V4. Monocular and binocular interactions between a Boundary Contour (BC) System and a Feature Contour (FC) System are developed. The BC System, defined by a hierarchy of oriented interactions, synthesizes an emergent and coherent binocular boundary segmentation from combinations of unoriented and oriented scenic elements. These BC System interactions instantiate a new theory of stereopsis and of how mechanisms of stereopsis are related to mechanisms of boundary segmentation. Interactions between the BC System and the FC System explain why boundary completion and segmentation processes become binocular at an earlier processing stage than do color and brightness perception processes. The new stereopsis theory includes a new model of how chromatically broadband cortical complex cells can be adaptively tuned to multiplex information about position, orientation, spatial frequency, positional disparity, and orientational disparity. These binocular cells input to spatially short-range competitive interactions (within orientations and between positions, followed by between orientations and within positions) that initiate suppression of binocular double images as they complete boundaries at scenic line ends and corners. The competitive interactions interact via both feedforward and feedback pathways with spatially long-range-oriented cooperative gating interactions that generate a coherent, multiple-scale, three-dimensional boundary segmentation as they complete the suppression of double-image boundaries. The completed BC System boundary segmentation generates output signals, called filling-in generators (FIGs) and filling-in barriers (FIBs), along parallel pathways to two successive FC System stages: the monocular syncytium and the binocular syncytium. FIB signals at the monocular syncytium suppress monocular color and brightness signals that are binocularly inconsistent and select binocularly consistent, monocular FC signals as outputs to the binocular syncytium. Binocular matching of these FC signals further suppresses binocularly inconsistent color and brightness signals. Binocular FC contour signals that survive these multiple suppressive events interact with FEB signals at the binocular syncytium to fill-in a multiplescale representation of form-and-color-in-depth. To achieve these properties, distinct syncytia correspond to each spatial scale of the BC System. Each syncytium is composed of opponent subsyncytia that generate output signals through a network of double-opponent cells. Although composed of unoriented wavelength-sensitive cells, double-opponent networks detect oriented properties of form when they interact with FIG signals, yet also generate nonselective properties of binocular rivalry. Electrotonic and chemical transmitter interactions within the syncytia are formally akin to interactions in HI horizontal cells of turtle retina. The cortical syncytia are hypothesized to be encephalizations of ancestral retinal syncytia. In addition to double-opponent-cell networks, electrotonic syncytial interactions, and resistive gating signals due to BC System outputs, the FC System processes also include habituative transmitters and non-Hebbian adaptive filters that maintain the positional and chromatic selectivity of FC interactions. Alternative perceptual theories are evaluated in light of these results. The theoretical circuits provide qualitatively new design principles and architectures for computer vision applications.

Visual information and skill level in time-to-collision estimation.

Abstract: Previous studies on the visual origin of time-to-collision (Tc) information have demonstrated that Tc estimates can be based solely on the processing of target expansion rate (optic variable tau). But in the simulated situations used (film clips), there was little reliable information on speed (owing to reduced peripheral vision) and distance (owing to the absence of binocular distance cues) available. In order to determine whether these kinds of information are also taken into account, it is necessary to take an approach where the subject receives a more complete visual input. Thus, an experiment conducted on a circuit under actual driving conditions is reported. Experienced drivers and beginners, who were passengers in a car, had to indicate the moment they expected a collision with a stationary obstacle to take place. Subjects were blindfolded after a viewing time of 3 s. The conditions for speed evaluation (normal versus restricted visual field) and distance evaluation (binocular versus monocular vision) by subjects were varied. The approach speed (30 and 90 km h-1) and actual Tc (3 and 6 s) were also varied. The results show that accuracy of Tc estimation increased with (i) normal visual field, (ii) binocular vision, (iii) higher speeds, and (iv) driving experience. These findings have been interpreted as indicating that both speed and distance information are taken into account in Tc estimation. They suggest furthermore that these two kinds of information may be used differently depending on the skill level of the subject. The results are discussed in terms of the complementarity of the various potentially usable visual means of obtaining Tc information.

Minimodularity and the Perception of Layout

Abstract: SUMMARY In natural vision, information overspecifies the relative distances between objects and their layout in three dimensions. Directed perception applies (Cutting, 1986), rather than direct or indirect perception, because any single source of information (or cue) might be adequate to reveal relative depth (or local depth order), but many are present and useful to observers. Such overspecification presents the theoretical problem of how perceivers use this multiplicity of information to arrive at a unitary appreciation of distance between objects in the environment. This article examines three models of directed perception: selection, in which only one source of information is used; addition, in which all sources are used in simple combination; and multiplication, in which interactions among sources can occur. To establish perceptual overspecification, we created stimuli with four possible sources of monocular spatial information, using all combinations of the presence or absence of relative size, height in the projection plane, occlusion, and motion parallax. Visual stimuli were computer generated and consisted of three untextured parallel planes arranged in depth. Three tasks were used: one of magnitude estimation of exocentric distance within a stimulus, one of dissimilarity judgment in how a pair of stimuli revealed depth, and one of choice judgment within a pair as to which one revealed depth best. Grouped and individual results of the one direct and two indirect scaling tasks suggest that perceivers use these sources of information in an additive fashion. That is, one source (or cue) is generally substitutable for another, and the more sources that are present, the more depth is revealed. This pattern of results suggests independent use of information by four separate, functional subsystems within the visual system, here called minimodules. Evidence for and advantages of mmimodularity are discussed.

The Role of Monocular Regions in Stereoscopic Displays

Abstract: Random-dot stereograms of an object standing out from a background always contain a monocular region at the side of the foreground object. This is equivalent to the monocularly occluded part of the background in the real-life viewing of one object in front of another. The role of these monocular regions in the stereoscopic process has not been investigated previously, although it is generally assumed that they are a source of difficulty in stereoscopic resolution because of the unmatchable texture within them. The basis of the present study was a prediction that the presence of texture within these regions would facilitate rather than retard stereoscopic processing. This prediction follows from a hypothesis that stereoscopic processing is initially located at disparity discontinuities. Unmatched regions are only found at such discontinuities, and could serve to locate them.

Magnification effects with imaging displays depend on scene content and viewing condition

Abstract: Previous research has shown that imaging displays require a degree of magnification to appear the same size as a natural view of the same scene. A single-lens reflex camera fitted with a zoom lens was used as an imaging device so that the magnification of four outdoor scenes could be varied. Subjects were required to adjust the focal length of the lens so that the perceived size of objects in the viewfinder matched that in normal direct viewing of the scene, either monocular or binocular. When viewed through the apparatus, scenes with more depth information produced smaller overestimates of judged size. When the normal direct view was monocular, smaller overestimates were produced than when the same scenes were viewed by normal direct binocular vision. The possible roles of scene content and oculomotor effects in judgments of size made with imaging displays are discussed.

Depth resolution in the pigeon.

Abstract: Pigeons possess a binocular visual field and a retinal region of higher cellular density pointing to the center of this overlap. These features and the precision of pecking behavior suggest that in this lateral-eyed bird cues other than monocular ones might participate in depth judgements. Pigeons were trained with an operant procedure to discriminate between luminous points differing in depth which appeared to the observer as floating in the dark. The accuracy of depth judgements was found to be a function of the ratio between the interstimulus distance and the mean eyes-to-stimulus distance. In a first test (experiment I) no external binocular disparity cues were available, the animal only seeing one luminous point at a time (near or far). In a second test (experiment II) where binocular disparity cues were available, the animal having this time to discriminate a pair of points placed at equal depth from a pair placed at unequal depths, only one pair being visible at a time, depth resolution did not improve. This suggests that, at least within the range of distances explored, the pigeon has no stereoscopic vision. Notwithstanding this, binocular cues do play a role, since when tests were done comparing binocular with monocular viewing (experiment III), monocular depth resolution was significantly worse.

Left-right visual field asymmetry in bistable motion perception.

Abstract: Twelve observers viewed two alternating frames, each consisting of three rectangular bars which were displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three elements moving as a whole (group movement), whereas with IFIs shorter than 40-60 ms the overlapping elements in each frame appeared stationary while the third element appeared to move from one end of the display to the other (end-to-end movement). The percentage of group movement responses in central viewing was compared to those obtained for stimulus presentation in the left and right visual fields (4 deg eccentricity), for opposite horizontal directions of motion. All ten right-handed subjects showed a left-field advantage in sensitivity to group movement. The two left-handed subjects showed a similar advantage in sensitivity with right-field presentation. The effects of monocular vision, hand used in the task, spatial frequency, and contrast on visual field asymmetry were all investigated in two right-handed subjects. None of these factors affected the left-right asymmetry.

"Abnormal fusion" of stereopsis and binocular rivalry.

Abstract: Wolfe (1986) has proposed a theory of binocular vision with the following characteristics: It consists of an exclusively binocular (AND) process, an either-eye binocular (OR) process, and two monocular (ONLY) processes. All these processes function simultaneously, and perception derives from the combination of their outputs. Critically, the theory asserts that binocular rivalry and stereopsis can be active at the same site in the visual field. We argue that Wolfe's theory is needlessly complex in that simultaneous action of binocular rivalry and stereopsis is unnecessary, yet it is unable to account for data on detection of monocular probes that are easy to explain within current models of binocular vision.

Helmet-mounted, binocular, holographic view finder with wide field of vision

Abstract: Binocular view finder enabling a wide field of vision, 60 DEG vertically by 120 DEG horizontally, to be obtained. It is constituted, for each monocular vision channel, by an image generator (1A), for example a miniature cathode ray tube, by an optical relay (2A), by a collimation and combination optical system bringing together a holographic (H1) mixer plate (3A) for transmitting the landscape channel and reflecting the image channel and by a biconvex combining device (4A) formed from two holographic spherical optical elements (41, 42) used on the axis (H2, H3) for transmitting the two channels with collimation by diffraction of the image channel. A circular axial zone of zero photometric yield is produced for each monocular vision and is compensated by the overlap of the binocular fields of vision and, additionally, by the production of hologram mirrors having variable-index modulation.

Accommodative adaptation to monocular and binocular stimuli

Abstract: Pre- and post-task measures of dark-focus (DF) were used to assess accommodative adaptation induced by a 45-s near-vision task at 33 cm. Adaptation was measured under monocular and binocular conditions for a group of 10 young emmetropic subjects (mean age 21.6 years). The accommodative response was measured objectively using an infrared optometer (Canon Autoref R-1). Post-task DF was sampled immediately after the task at 1-s intervals over a 90-s period. No significant difference in accommodative adaptation was observed between the monocular and binocular near-vision tasks. The implications of this finding are discussed with regard to the oculomotor constituents of the closed-loop accommodative response.

Generating the initial hypothesis using perspective invariants for a 2D image and 3D model matching

Abstract: Generation of the initial matching hypothesis for a model-based monocular vision system is presented. The primitive shape description of images is a set of line segments and the model is automatically constructed from a sequence of stereo views. The key points of the approach are the use of vanishing points and other perspective invariants such as collinearity, connectivity, and the use of double ratios to get rid of matching ambiguities. >

Acquired Monocular Disability.

Abstract: This paper addresses the handicapping effects of acquired monocular impairment. The author stresses the importance of informing professionals about monocular impairment and encourages them to pursu...

A new approach to machine-based perception of monocular images

Abstract: A novel approach to machine-based visual perception of monocular images is described and initial recognition results are presented. The approach uses a recursive procedure to generate a series of reconstructed versions of the raw video image. The procedure is motivated by certain perceptual organization functions of the human visual system. Recognition of object categories is attempted at each step by comparing the newly generated regions to stored object categories. Category retrieval is carried out using a software-based content-addressing scheme which provides access to complete object representations in memory using incomplete portions of the representation. The category-representation scheme is sufficiently general to allow a variety of poorly correlated images of specific category examples to be represented and recognized by a single general category representation. These properties are illustrated using a group of distorted, defective, and idealized images of ASCII A's and handguns. >

Assessment of the Driving Behavior of Visually Handicapped Persons

Abstract: A car is an integral part of our world. Youngsters apply for a driver’s license at an early age. They obtain their driver’s license after a theoretical and practical test. Getting this license does not only mean the driver is found capable to conduct a vehicle, but also that the driver can react adequately in any traffic situation. A driving test is once-only. Nevertheless it is not unthinkable that at a certain age one can develop an affection of some kind which might make it difficult to drive a car. One type of handicap that interferes with driving is a reduced visual acuity. The European guidelines of 4 December 1980 states that a visual acuity of 5/10 for binocular vision and of 8/10 for monocular vision was necessary to obtain and keep a driver’s license. In 1986 a project with a new formulation was set up. It proposed to require a minimum vision of 6/10 for monophthalms as well as for others. These propositions are not based on a study of driving proficiency. They are arbitrary decisions. The arbitrariness is very well illustrated by the requirements and big differences between several countries with a comparable traffic-density. The authors made an effort to lay down well grounded standards and the authors questioned a group of low vision patients who drive a car.