Simon J Watt

• BSc, MSc, PhD
• Professor (Associate) at Bangor University

Stereoscopic imagery often aims to evoke three-dimensional (3-D) percepts that are accurate and realistic-looking. The “gap” between 3-D imagery and real scenes is small, but focus cues typically remain incorrect because images are displayed on a single focal plane. Research has concentrated on the resulting vergence–accommodation conflicts. Yet, i...

Errors of touch localisation after injury to the nerves of the hand are common, and their measurement is of considered importance for evaluating functional recovery. Available empirical accounts have significant methodological limitations, however, and a quantitatively rigorous and detailed description of touch localisation in nerve injury is lacki...

Human manual dexterity relies critically on touch. Robotic and prosthetic hands are much less dexterous and make little use of the many tactile sensors available. We propose a framework modeled on the hierarchical sensorimotor controllers of the nervous system to link sensing to action in human-in-the-loop, haptically enabled, artificial hands. Sum...

With well-established methods for producing photo-realistic results, the next big challenge of graphics and display technologies is to achieve perceptual realism --- producing imagery indistinguishable from real-world 3D scenes. To deliver all necessary visual cues for perceptual realism, we built a High-Dynamic-Range Multi-Focal Stereo Display tha...

The brain must interpret sensory input from diverse receptor systems to estimate object properties. Much has been learned about the brain mechanisms behind these processes in vision, while our understanding of haptic perception remains less clear. Here we examined haptic judgments of object size, which require integrating multiple cutaneous and pro...

In the past few years a new scenario for robot-based applications has emerged. Service and mobile robots have opened new market niches. Also, new frameworks for shop-floor robot applications have been developed. In all these contexts, robots are requested to perform tasks within open-ended conditions, possibly dynamically varying. These new require...

Ideal grasping movements should maintain an appropriate probability of success, while controlling movement-related costs, in the presence of varying visual (and motor) uncertainty. It is often assumed that the probability of errors is managed by adjusting a margin for error in hand opening (e.g., opening the hand wider with increased visual uncerta...

Binocular vision is often assumed to make a specific, critical contribution to online visual control of grasping by providing precise information about the separation between digits and object. This account overlooks the ‘viewing geometry’ typically encountered in grasping, however. Separation of hand and object is rarely aligned precisely with the...

When we feel and see an object, the nervous system integrates visual and haptic information optimally, exploiting the redundancy in multiple signals to estimate properties more precisely than is possible from either signal alone. We examined whether optimal integration is similarly achieved when using articulated tools. Such tools (tongs, pliers, e...

We have previously investigated the effectiveness of a custom-built virtual environment in assisting training of a ventriculostomy procedure, which is a commonly performed procedure by a neurosurgeon and a core task for trainee surgeons. The training tool (called VCath) was initially developed as a low-fidelity app for a tablet platform to provide...

Conventional stereoscopic imagery presents conflicting stimuli to vergence and accommodation. With sufficient conflict, vergence-accommodation coupling causes inaccurate responses in one or both systems, impairing stereoscopic depth perception, or preventing it altogether. We examined tolerance of stereo depth perception to stimuli presented in-fro...

Many people who first see a high dynamic range (HDR) display get the impression that it is a 3D display, even though it does not produce any binocular depth cues. Possible explanations of this effect include contrast-based depth induction and the increased realism due to the high brightness and contrast that makes an HDR display “like looking throu...

When we hold an object while looking at it, estimates from visual and haptic cues to size are combined in a statistically optimal fashion, whereby the “weight” given to each signal reflects their relative reliabilities. This allows object properties to be estimated more precisely than would otherwise be possible. Tools such as pliers and tongs syst...

We have designed a configurable virtual environment to train rugby ball passing skills. Seeking to validate the system’s ability to correctly aid training, two experiments were performed. Ten participants took part in ball passing activities, which were used to compare the combinations of different user positions relative to the physical screen, th...

Background / Purpose: Work has been done to determine the extent of the zone of comfort for 3-D stereoscopic content (1) in terms of the vergence-accommodation conflicts that can be tolerated. Less has been done to understand the range within stereo depth perception. We examined stereo performance at different vergence-accommodation conflicts, an...

We have designed and developed a virtual environment to train rugby ball passing skills. Seeking to validate the system's ability to correctly aid training, an initial experiment was performed to examine the effect of stereoscopic technology and the physical screen's setup on the user's ability to perceive virtual distances correctly. Four particip...

Ideally, viewing stereoscopic three-dimensional (S3D) media should be much like viewing the real world, in that it creates a compelling and immersive sense of the three-dimensional structure of the portrayed scene, without producing unwanted perceptual artefacts or aversive symptoms in the viewer. With the recent growth in S3D cinema, television an...

The vergence-accommodation conflict in conventional stereo displays causes poor stereoscopic performance and observer discomfort. We examined the effectiveness of multiple-focal-plane displays in overcoming these issues. Specifically, we examined a technique referred to as 'depth filtering', in which continuous variations in focal distance are appr...

Stereoscopic displays have become important for many applications, including operation of remote devices, medical imaging, surgery, scientific visualization, and computer-assisted design. But the most significant and exciting development is the incorporation of stereo technology into entertainment: specifically, cinema, television, and video games....

Conventional stereoscopic displays present images on a single focal plane. The resulting mismatch between the stimuli to the eyes' focusing response (accommodation) and to convergence causes fatigue and poor stereo performance. One solution is to distribute image intensity across a number of widely spaced image planes—a technique referred to as dep...

Conventional stereoscopic displays present conflicting stimuli to vergence and accommodation, causing fatigue, discomfort, and poor stereo depth perception. One promising solution is 'depth filtering', in which continuous variations in focal distance are simulated by distributing image intensity across multiple focal planes. The required image-plan...

Optimising haptic sensitivity in visual-haptic interfaces can have important benefits, particularly in situations where visual information is relatively unreliable (for example in surgical devices, where there is often a lack of normal visual depth cues). Many haptic devices alter the normal relationship between object size and hand opening, and so...

Tools such as pliers systematically change the relationship between an object's size and the hand opening required to grasp it. Previous work suggests the brain takes this into account, integrating visual and haptic size information that refers to the same object, independent of the similarity of the 'raw' visual and haptic signals (Takahashi et al...

Accommodation operates to optimise retinal-image contrast. There is a long-standing debate, however, about the role of different spatial frequencies. The fine-tuning hypothesis posits that high frequencies play an increasing role as the system approaches sharp focus. Yet empirical data show that adding mid-range frequencies (above 6–8 cpd) has litt...

Conventional stereoscopic displays present images on a single focal plane. The resulting mismatch between the stimuli to the eyes' focusing response (accommodation) and to convergence causes fatigue and poor stereo performance. One promising solution is to distribute image intensity across a number of relatively widely spaced image planes - a techn...

When we grasp with one eye covered, the finger and thumb are typically opened wider than for binocularly guided grasps, as if to build a margin-for-error into the movement. Also, patients with visual form agnosia can have profound deficits in their (otherwise relatively normal) grasping when binocular information is removed. One interpretation of t...

3d displays on digital media are often perceived as different from the portrayed object or scene, even when the display creates the "correct" 2d retinal images. In principle, there are at least three depth cues created by digital displays that could contribute to such distortions: 1) inappropriate focus cues, 2) pixelization, and 3) inappropriate m...

It has frequently been reported that stereoscopically-defined, slanted surfaces have greater perceived slant when the rotation axis is horizontal (tilt = 90 deg) than when it is vertical (tilt = 0 deg). It has also been observed in cue-conflict experiments that more weight is given to the slant specified by monocular cues when tilt = 90 deg than wh...

To recover absolute depth from binocular disparity, horizontal disparities must be scaled by an estimate of fixation distance. Conventional 3d digital displays present stimuli at one focal distance and this could result in distortions of perceived depth at simulated distances other than the actual distance to the display. To investigate this we ind...

For integration of information from vision and haptics to be effective, the brain should only combine information referring to the same object. This could be achieved by considering the similarity of signals in the two sensory channels. For example, if there is a large conflict between two size estimates it is unlikely that they originate from the...

Most stereoscopic displays present images at a single focal plane, resulting in "conflicts" between the stimuli to vergence and accommodation. Minimizing these conflicts is beneficial because they can cause distorted depth percepts, visual fatigue, and reduced stereoscopic performance. One proposed solution is to present a sum of images at multiple...

Studies examining the role of different depth cues in the control of grasping have typically presented three or fewer objects at three or fewer distances. This raises the possibility that participants learn the stimulus set. If so, even poor depth information could appear to support reliable grasping, provided that it was sufficient to identify whi...

Haptics technologies are frequently used in virtual environments to allow participants to touch virtual objects. Medical applications are no exception and a wide variety of commercial and bespoke haptics hardware solutions have been employed to aid in the simulation of medical procedures. Intuitively the use of haptics will improve the training of...

Conventional stereoscopic displays present images at a fixed focal distance. Depth variations in the depicted scene therefore result in conflicts between the stimuli to vergence and to accommodation. The resulting decoupling of accommodation and vergence responses can cause adverse consequences, including reduced stereo performance, difficulty fusi...

Conventional digital displays present stimuli at only one focal distance because the light comes from a single surface. When the display is meant to create a 3d percept, two significant problems occur. First, depth information from accommodation and the blur gradient is uncontrolled, which can lead to distortions in perceived 3d structure. Second,...

When integrating signals from vision and haptics the brain must solve a "correspondence problem" so that it only combines information referring to the same object. An invariant spatial rule could be used when grasping with the hand: here the two signals should only be integrated when the estimate of hand and object position coincide. Tools complica...

The role of binocular vision in grasping has frequently been assessed by measuring the effects on grasp kinematics of covering one eye. These studies have typically used three or fewer objects presented at three or fewer distances, raising the possibility that participants learn the properties of the stimulus set. If so, even relatively poor visual...

Conventional stereo displays provide incorrect focus cues because the image is presented on a single surface. This is known to cause a number of aversive symptoms in users, including fatigue and discomfort. Multiple-focal-plane displays have been proposed as a solution to this problem. In principle, a continuous range of focal distances can be simu...

Focus cues specify inappropriate 3-D scene parameters in conventional displays because the light comes from a single surface, independent of the depth relations in the portrayed scene. This can lead to distortions in perceived depth, as well as discomfort and fatigue due to the differing demands on accommodation and vergence. Here we examine the ef...

Depth information from focus cues--accommodation and the gradient of retinal blur--is typically incorrect in three-dimensional (3-D) displays because the light comes from a planar display surface. If the visual system incorporates information from focus cues into its calculation of 3-D scene parameters, this could cause distortions in perceived dep...

How does the visual system combine information from different depth cues to estimate three-dimensional scene parameters? We tested a maximum-likelihood estimation (MLE) model of cue combination for perspective (texture) and binocular disparity cues to surface slant. By factoring the reliability of each cue into the combination process, MLE provides...

The present study examined the effects of a pre-movement delay on the kinematics of prehension in middle childhood. Twenty-five children between the ages of 5 and 11 years made visually open-loop reaches to two different sized objects at two different distances along the midline. Reaches took place either (i) immediately, or (ii) 2 s after the occl...

Typical stereo displays provide incorrect focus cues because the light comes from a single surface. We describe a prototype stereo display comprising two independent fixed-viewpoint volumetric displays. Like autostereoscopic volumetric displays, fixed-viewpoint volumetric displays generate near-correct focus cues without tracking eye position, beca...

The present study was designed to assess the importance of binocular information (i.e. binocular disparity and angle of convergence) in the control of prehension. Previous studies which have addressed this question have typically used the same experimental manipulation: comparing prehensile movements executed either under binocular conditions to th...

The primary visual sources of depth and size information are binocular cues and motion parallax. Here, the authors determine the efficacy of these cues to control prehension by presenting them in isolation from other visual cues. When only binocular cues were available, reaches showed normal scaling of the transport and grasp components with object...

Binocular cues have been shown previously to make an important contribution to the control of natural prehensile movements in adults [Visual Cognition 4 (1997) 113, Vision Research 32 (1992) 1513, Neuropsychologia 38 (2000) 1473]. The present study examined the role of binocular vision in the control of prehension in middle childhood. Fourteen chil...

Increasingly, binocular disparity has become commonplace in telepresence systems despite the additional cost of its provision. Experiments comparing performance under monocular and binocular viewing are often cited as justification for its use. Here we question whether this experimental comparison and provide an important set of data which compares...

Although binocular disparity can in principle provide absolute depth information, perceived stereoscopic depth depends on the relative disparities between points and their spatial arrangement. An example of this is the stereoscopic anisotropy--observers typically perceive less depth for stereoscopic surfaces when depth varies in the horizontal dire...

Neuropsychological results support the proposal that the human visual system is organised into distinct processing pathways, one for conscious perception and one for the control of action. Here, we compare perceptual and action responses following a pre-response-delay. Experiment 1 required participants to reproduce remembered locations and found t...

Recent evidence suggests that the visual control of prehension may be less dependent on binocular information than has previously been thought. Studies investigating this question, however, have generally only examined reaches to single objects presented in isolation, even though natural prehensile movements are typically directed at objects in clu...

Binocular telepresence systems afford the opportunity of increasing the inter-camera distance (ICD) beyond the normal interocular distance (IOD) which magnifies the magnitude of the disparity information. This improves performance in nulling and matching tasks. Here we examine whether telepresent observers can learn to use enhanced disparities to a...

The experiments reported here were designed to address two aims. Th first was to determine the sufficiency of head- generated motion parallax, when present in isolation, for the control of natural prehensile movements. The second was to assess the consequences of providing enhanced parallax information for prehension. Enhanced parallax was created...

It has been observed that wearing goggles that restrict the field of view (FOV) causes familiar objects to appear both smaller and nearer. To investigate this further, we examined the effect of a range of field sizes (4 degrees, 8 degrees, 16 degrees, 32 degrees and 64 degrees) on estimates of object distance and object size used to control reachin...

The control of inter-camera distance (ICD) can be used to change the range of binocular disparities available from a visual scene viewed remotely. Binocular disparity is considered pre-eminent in the control of reaching behavior. One reason for this is that once suitably scaled it can specify metrical depth relationships within a scene. Such inform...

Binocular cues are typically considered to be pre-eminent in the control of reaching and grasping behaviour. However, in the absence of such information prehension movements can still be accurate and reliable. The present study therefore was designed to assess further the contribution of binocular information in the control of human reaching and gr...

A new visual illusion is reported in which randomly positioned squares that are perfectly aligned with the horizontal and vertical appear slightly rotated about their midpoints ('jittered') relative to each other. Possible mechanisms for the illusion have been explored in a series of three experiments. Experiment 1 showed that, unlike the Münsterbe...

Determining how people perceive distance is a central issue in the study of visual perception. Whilst near-distance perception has been extensively researched, far-distance perception has received little attention. We review the literature and illustrate key points with new data, focusing on analysis of available information/cues, degree of accurac...

Acquisition of the skill of medical image inspection could be due to changes in visual search processes, 'low-level' sensory learning, and higher level 'conceptual learning.' Here, we report two studies that investigate the extent to which learning in medical image inspection involves low- level learning. Early in the visual processing pathway cell...

Thesis (Ph. D.)--University of Surrey, 2001.