Various visual cues provide information about depth and shape in a scene. When several of these cues are simultaneously available in a single location in the scene, the visual system attempts to combine them. In this paper, we discuss three key issues relevant to the experimental analysis of depth cue combination in human vision: cue promotion, dynamic weighting of cues, and robustness of cue combination. We review recent psychophysical studies of human depth cue combination in light of these issues. We organize the discussion and review as the development of a model of the depth cue combination process termed modified weak fusion (MWF). We relate the MWF framework to Bayesian theories of cue combination. We argue that the MWF model is consistent with previous experimental results and is a parsimonious summary of these results. While the MWF model is motivated by normative considerations, it is primarily intended to guide experimental analysis of depth cue combination in human vision. We describe experimental methods, analogous to perturbation analysis, that permit us to analyze depth cue combination in novel ways. In particular these methods allow us to investigate the key issues we have raised. We summarize recent experimental tests of the MWF framework that use these methods. Depth Multiple cues Sensor fusion

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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

Augmented reality (AR) systems combine three-dimensional computer-generated imagery with the view of the real environment in order to make unseen objects visible or to present additional information. A critical problem is that the computer-generated objects do not currently remain correctly registered with the real environment---objects aligned from one viewpoint appear misaligned from another and appear to swim about as the viewer moves. This registration error is caused by a number of factors, such as system delay, optical distortion, and tracker measurement error, and is difficult to correct with existing technology. This dissertation presents a registration error model for AR systems and uses it to gain insight into the nature and severity of the registration error caused by the various error sources. My thesis is that a mathematical error model enables the system architect to determine . which error sources are the most significant, . the sensitivity of the net registration error to each error, . the nature of the distortions caused by each type of error, . the level of registration accuracy one can expect, and also provides insights on how best to calibrate the system. Analysis of a surgery planning application yielded the following main results: . Even for moderate head velocities, system delay causes more registration error than all other sources combined; . Using the eye's center of rotation as the eyepoint in the computer graphics model reduces the error due to eye rotation to zero for points along the line of gaze. This should obviate the need for eye tracking; . Tracker error is a significant problem both in head tracking and in system calibration; . The World coordinate system should be omitted when possible; . Optical distortion is a significant err...

The task of visual search is to determine as rapidly as possible whether a target item is present or absent in a display. Rapidly detected items are thought to contain features that correspond to primitive elements in the human visual system. In previous theories, it has been assumed that visual search is based on simple two-dimensional features in the image. However, visual search also has access to another level of representation, one that describes properties in the corresponding three-dimensional scene. Among these properties are three dimensionality and the direction of lighting, but not viewing direction. These findings imply that the parallel processes of early vision are much more sophisticated than previously assumed. It is easy to detect a vertical line placed among a group of horizontal lines. The vertical line “pops out”, drawing attention to itself regardless of how many horizontal lines are present. In contrast, searching for a T-shaped target among L-shaped distractors requires conscious effort, and search time increases linearly with the number of L-shaped distractors in the display. These two classes of search exemplify the visual search paradigm, a useful tool for determining the primitive elements of early human vision.

1.1 Four assays of quality................................................................ 4 1.2 The structure of appearance.................................................... 11 1.3 Intrinsic versus relational........................................................ 13 1.4 Four refutations....................................................................... 17 2. Qualities and their Places................................................................ 25 2.1 The appearance of space......................................................... 25 2.2 Some brain-mind mysteries..................................................... 26 2.3 Spatial qualia........................................................................... 33 2.4 Appearances partitioned.......................................................... 35 2.5 Ties that bind........................................................................... 38 2.6 Feature-placing introduced...................................................... 43 3 Places Phenomenal and Real............................................................ 47 3.1 Space-time regions.................................................................. 47 3.2 Three varieties of visual field.................................................. 50 3.3 Why I am not an array of impressions..................................... 55 3.4 Why I am not an intentional object......................................... 58 3.5 Sensory identification.............................................................. 61 3.6 Some examples of sensory reference....................................... 66

Abstract not found

We test hypotheses concerning human cue combination in a slant estimation task. Observers

this paper that you hold in your hands. The question is whether the rich spatial structure of this experience before you is the physical paper itself, or whether it is an internal data structure or pattern of activation within your physical brain. Although this issue is not much discussed in contemporary psychology, it is an old debate that has resurfaced several times in psychology, but the continued failure to reach consensus on this issue continues to bedevil the debate on the functional role of sensory processing. The reason for the continued confusion is that both direct and indirect realism are frankly incredible, although each is incredible for different reasons. 6 2.1 Problems with Direct Realism The direct realist view is incredible because it suggests that we can have experience of objects out in the world directly, beyond the sensory surface, as if bypassing the chain of sensory processing. For example if light from this paper is transduced by your retina into a neural signal which is transmitted from your eye to your brain, then the very first aspect of the paper that you can possibly experience is the information at the retinal surface, or the perceptual representation downstream of it in your brain. The physical paper itself lies beyond the sensory surface and therefore must be beyond your direct experience. But the perceptual experience of the page stubbornly appears out in the world itself instead of in your brain, in apparent violation of everything we know about the causal chain of vision. Gibson explicitly defended the notion of direct perception, and spoke as if perceptual processing occurs somehow out in the world itself rather than as a computation in the brain based on sensory input (Gibson 1972 p. 217 & 239). Significantly, Gibson refused to di...

Sensitivity of 8-week-old infants to optical flow specifying the shape of a three-dimensional object was assessed. Infants viewed kinetic random-dot displays that specified three-dimensional cubes. The cubes were identical except for the presence or absence of an interior corner. Half of the infants viewed the full display. The other half viewed the central region of the displays, where the flow specifying the presence or absence of the corner differed. Infants in the full-view condition looked significantly longer to a novel cube than to the familiar cube following habituation. In contrast, infants in the partial-view condition looked equally to the novel and familiar cubes, ruling out the possibility that infants who viewed the full displays merely discriminated differences in motion in the central region of the two displays. These findings suggest that infants as young as 8 weeks perceive three-dimensional object shape from optic flow. Perception of the world based on motion has occupied perceptual psychologists for a number of decades (see Braunstein, 1962, for a review). Pioneering work by Helmholtz (1909/1924) suggested that the differential motion of objects located at different distances was an effective cue to depth, and informal experiments conducted