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Lew B. Stelmach

Bio: Lew B. Stelmach is an academic researcher from University of Alberta. The author has contributed to research in topics: Image quality & Stereoscopy. The author has an hindex of 16, co-authored 32 publications receiving 1349 citations.

Papers
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Journal ArticleDOI
TL;DR: The findings support the notion that attention affects the speed of transmission of information in the visual system and a model is proposed in which the temporal profile of visual responses is affected by directed attention.
Abstract: The present research examined the effects of directed attention on speed of information transmission in the visual system. Ss judged the temporal order of 2 stimuli while directing attention toward 1 of the stimuli or away from both stimuli. Perception of temporal order was influenced by directed attention: Given equal onset times, the attended stimulus appeared to occur before the unattended stimulus. Direction of attention also influenced the perception of simultaneity. The findings support the notion that attention affects the speed of transmission of information in the visual system. To account for the pattern of temporal order and simultaneity judgments, a model is proposed in which the temporal profile of visual responses is affected by directed attention.

332 citations

Journal ArticleDOI
TL;DR: It was found that spatial filtering of one channel of a stereo video-sequence may be an effective means of reducing the transmission bandwidth: the overall sensation of depth was unaffected by low-pass filtering, while ratings of quality and of sharpness were strongly weighted towards the eye with the greater spatial resolution.
Abstract: We explored the response of the human visual system to mixed-resolution stereo video-sequences, in which one eye view was spatially or temporally low-pass filtered. It was expected that the perceived quality, depth, and sharpness would be relatively unaffected by low-pass filtering, compared to the case where both eyes viewed a filtered image. Subjects viewed two 10-second stereo video-sequences, in which the right-eye frames were filtered vertically (V) and horizontally (H) at 1/2 H, 1/2 V, 1/4 H, 1/4 V, 1/2 H 1/2 V, 1/2 H 1/4 V, 1/4 H 1/2 V, and 1/4 H 1/4 V resolution. Temporal filtering was implemented for a subset of these conditions at 1/2 temporal resolution, or with drop-and-repeat frames. Subjects rated the overall quality, sharpness, and overall sensation of depth. It was found that spatial filtering produced acceptable results: the overall sensation of depth was unaffected by low-pass filtering, while ratings of quality and of sharpness were strongly weighted towards the eye with the greater spatial resolution. By comparison, temporal filtering produced unacceptable results: field averaging and drop-and-repeat frame conditions yielded images with poor quality and sharpness, even though perceived depth was relatively unaffected. We conclude that spatial filtering of one channel of a stereo video-sequence may be an effective means of reducing the transmission bandwidth.

217 citations

Journal ArticleDOI
TL;DR: It is concluded that blur, but not blockiness, is an acceptable form of monocular degradation, provided that binocular vision assigns greater weight to the nondegraded input.
Abstract: For efficient storage and transmission of stereoscopic images over bandwidth-limited channels, compression can be achieved by degrading 1 monocular input of a stereo pair and maintaining the other at the desired quality. The desired quality of the fused stereoscopic image can be achieved, provided that binocular vision assigns greater weight to the nondegraded input. A psychophysical matching procedure was used to determine if such over-weighting occurred when the monocular degradation included blur or blocking artifacts. Over-weighting of the nondegraded input occurred for blur, but under-weighting of the nondegraded input occurred for blockiness. Some participants exhibited ocular dominance, but this did not affect the blur results. The authors conclude that blur, but not blockiness, is an acceptable form of monocular degradation.

103 citations

Journal ArticleDOI
TL;DR: The relationship between eye movements and movements of attention was examined in a series of 6 experiments as mentioned in this paper, and it was shown that endogenous movements of the attentional system were slower than the movement of the eyes and participants were able to hold attention at one location while executing an eye movement to another location.
Abstract: The relationship between eye movements and movements of attention was examined in a series of 6 experiments. A temporal order judgment technique was used to index attentional allocation. The results showed that endogenous movements of attention were slower than movements of the eyes and that the participants were able to hold attention at one location while executing an eye movement to another location. Under conditions of exogenous cueing, attention moved rapidly to the cued location, in advance of the eyes. These findings challenge the prevailing view that ocular movements must necessarily be preceded by a movement of The human visual system has two means by which to sample information from a scene, ocular and attentional. Ocular sampling involves movements of the eyes and consists of a series of fixations from one location to another. Attentional sampling has been described as a movement of an attentional spotlight (Posner, Snyder, & Davidson, 1980) or beam (Eriksen & Yeh, 1985) or as the repositioning of an attentional gradient (LaBerge & Brown, 1989). An important issue concerns the relationship between the ocular and the attentional systems and the manner in which the two systems interact. It is accepted that the ocular system does not constrain the attentional system insofar as attention can be moved in the visual field while the eyes remain fixated at one position. The extent to which attention constrains eye movements, however, has not been resolved. One possibility is that the eyes cannot be moved to an unattended location in the visual field; that is, prior to each saccade, attention must move ahead of the eyes to select the next fixation location. Another possibility is that eye movements can occur independently of attention such that the eyes can be moved to a location in the visual field that has not been targeted by attention. In the present research, we studied whether saccadic eye movements can occur independently

83 citations

Proceedings ArticleDOI
TL;DR: The main finding was that viewers preferred the stereoscopic version over the non-stereoscopic version of the sequences, provided that the sequence did not contain noticeable stereo artifacts, such as exaggerated disparity.
Abstract: In comparison to conventional displays, 3D stereoscopic displays convey additional information about the 3D structure of a scene by providing information that can be used to extract depth. In the present study we evaluated the psychovisual impact of stereoscopic images on viewers. Thirty-three non-expert viewers rated sensation of depth, perceived sharpness, subjective image quality, and relative preference for stereoscopic over non-stereoscopic images. Rating methods were based on procedures described in ITU- Rec. 500. Viewers also rated sequences in which the left- and right-eye images were processed independently, using a generic MPEG-2 codec, at bit-rates of 6, 3, and 1 Mbits/s. The main finding was that viewers preferred the stereoscopic version over the non-stereoscopic version of the sequences, provided that the sequence did not contain noticeable stereo artifacts, such as exaggerated disparity. Perceived depth was rated greater for stereoscopic than for non-stereoscopic sequences, and perceived sharpness of stereoscopic sequences was rated the same or lower compared to non-stereoscopic sequences. Subjective image quality was influenced primarily by apparent sharpness of the video sequences, and less so by perceived depth.

78 citations


Cited by
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Journal ArticleDOI
TL;DR: The basic theme of the review is that eye movement data reflect moment-to-moment cognitive processes in the various tasks examined.
Abstract: Recent studies of eye movements in reading and other information processing tasks, such as music reading, typing, visual search, and scene perception, are reviewed. The major emphasis of the review is on reading as a specific example of cognitive processing. Basic topics discussed with respect to reading are (a) the characteristics of eye movements, (b) the perceptual span, (c) integration of information across saccades, (d) eye movement control, and (e) individual differences (including dyslexia). Similar topics are discussed with respect to the other tasks examined. The basic theme of the review is that eye movement data reflect moment-to-moment cognitive processes in the various tasks examined. Theoretical and practical considerations concerning the use of eye movement data are also discussed.

6,656 citations

Journal Article
TL;DR: In this article, the authors propose that the brain produces an internal representation of the world, and the activation of this internal representation is assumed to give rise to the experience of seeing, but it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness.
Abstract: Many current neurophysiological, psychophysical, and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The outside world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the governing laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Several lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual \"filling in,\" visual stability despite eye movements, change blindness, sensory substitution, and color perception.

2,271 citations

Journal ArticleDOI
TL;DR: In this article, the authors propose that the brain produces an internal representation of the world, and the activation of this internal representation is assumed to give rise to the experience of seeing, but it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness.
Abstract: Many current neurophysiological, psychophysical, and psychological approaches to vision rest on the idea that when we see, the brain produces an internal representation of the world. The activation of this internal representation is assumed to give rise to the experience of seeing. The problem with this kind of approach is that it leaves unexplained how the existence of such a detailed internal representation might produce visual consciousness. An alternative proposal is made here. We propose that seeing is a way of acting. It is a particular way of exploring the environment. Activity in internal representations does not generate the experience of seeing. The outside world serves as its own, external, representation. The experience of seeing occurs when the organism masters what we call the governing laws of sensorimotor contingency. The advantage of this approach is that it provides a natural and principled way of accounting for visual consciousness, and for the differences in the perceived quality of sensory experience in the different sensory modalities. Several lines of empirical evidence are brought forward in support of the theory, in particular: evidence from experiments in sensorimotor adaptation, visual “filling in,” visual stability despite eye movements, change blindness, sensory substitution, and color perception.

2,264 citations

Book
01 Jan 1994
TL;DR: Part 1 Foundations: introduction the era of decentralization, Constructions: constructionism LEGO/logo StarLogo objects and parallelism and Reflections: the centralized mindset beyond the decentralized mindset.
Abstract: Part 1 Foundations: introduction the era of decentralization. Part 2 Constructions: constructionism LEGO/logo StarLogo objects and parallelism. Part 3 Explorations: simulations and stimulations slime mould artificial ants traffic jams termites turtles and frogs turtle ecology new turtle geometry forest fire recursive trees. Part 4 Reflections: the centralized mindset beyond the centralized mindset. Part 5 Projections: growing up. Appendices: student participants StarLogo overview.

1,023 citations

Journal ArticleDOI
TL;DR: The E-Z Reader model as mentioned in this paper ) is a general model of eye movement control in reading that relates cognitive processing (specifically aspects of lexical access) to eye movements in reading.
Abstract: The authors present several versions of a general model, titled the E-Z Reader model, of eye movement control in reading. The major goal of the modeling is to relate cognitive processing (specifically aspects of lexical access) to eye movements in reading. The earliest and simplest versions of the model (E-Z Readers 1 and 2) merely attempt to explain the total time spent on a word before moving forward (the gaze duration) and the probability of fixating a word; later versions (E-Z Readers 3-5) also attempt to explain the durations of individual fixations on individual words and the number of fixations on individual words. The final version (E-Z Reader 5) appears to be psychologically plausible and gives a good account of many phenomena in reading. It is also a good tool for analyzing eye movement data in reading. Limitations of the model and directions for future research are also discussed.

1,010 citations