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Abstract
Abstract Saccadic accuracy requires that the control signal sent to the motor neurons must be the right size to bring the fovea to the target, whatever the initial position of the eyes (and corresponding state of the eye muscles). Clinical and experimental evidence indicates that the basic machinery for generating saccadic eye movements, located in the brainstem, is not accurate: learning to make accurate saccades requires cerebellar circuitry located in the posterior vermis and fastigial nucleus. How do these two circuits interact to achieve adaptive control of saccades? A model of this interaction is described, based on Kawato's principle of feedback-error-learning. Its three components were (1) a simple controller with no knowledge of initial eye position, corresponding to the superior colliculus; (2) Robinson's internal feedback model of the saccadic burst generator, corresponding to preoculomotor areas in the brain-stem; and (3) Albus's Cerebellar Model Arithmetic Computer (CMK), a neural net model of the cerebellum. The connections between these components were (I) the simple feedback controller passed a (usually inaccurate) command to the pulse generator, and (2) a copy of this command to the CMAC; (3) the CMAC combined the copy with information about initial eye position to (4) alter the gain on the pulse generator's internal feedback loop, thereby adjusting the size of burst sent to the motor neurons. (5) If the saccade were inaccurate, an error signal from the feedback controller adjusted the weights in the CMAC. It was proposed that connection (2) corresponds to the mossy fiber projection from superior colliculus to oculomotor vermis via the nucleus reticularis tegmenti pontis, and connection (5) to the climbing fiber projection from superior colliculus to the oculomotor vermis via the inferior olive. Plausible initialization values were chosen so that the system produced hypometric saccades (as do human infants) at the start of learning, and position-dependent hypermetric saccades when the cerebellum was removed. Simulations for horizontal eye movements showed that accurate saccades from any starting position could be learned rapidly, even if the error signal conveyed only whether the initial saccade were too large or too small. In subsequent tests the model adapted realistically both to simulated weakening of the eye muscles, and to intrasaccadic displacement of the target, thereby mimicking saccadic plasticity in adults. The architecture of the model may therefore offer a functional explanation of hitherto mysterious tectocerebellar projections, and a framework for investigating in greater detail how the cerebellum adaptively controls saccadic accuracy.
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Whyte MP, Greenberg CR, Salman NJ, Bober MB, McAlister WH, Wenkert D, Van Sickle BJ, Simmons JH, Edgar TS, Bauer ML, Hamdan MA, Bishop N, Lutz RE, McGinn M, Craig S, Moore JN, Taylor JW, Cleveland RH, Cranley WR, Lim R, Thacher TD, Mayhew JE, Downs M, Millán JL, Skrinar AM, Crine P, Landy H. Enzyme-replacement therapy in life-threatening hypophosphatasia. N Engl J Med 2012; 366:904-13. [PMID: 22397652 DOI: 10.1056/nejmoa1106173] [Citation(s) in RCA: 350] [Impact Index Per Article: 29.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND Hypophosphatasia results from mutations in the gene for the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). Inorganic pyrophosphate accumulates extracellularly, leading to rickets or osteomalacia. Severely affected babies often die from respiratory insufficiency due to progressive chest deformity or have persistent bone disease. There is no approved medical therapy. ENB-0040 is a bone-targeted, recombinant human TNSALP that prevents the manifestations of hypophosphatasia in Tnsalp knockout mice. METHODS We enrolled infants and young children with life-threatening or debilitating perinatal or infantile hypophosphatasia in a multinational, open-label study of treatment with ENB-0040. The primary objective was the healing of rickets, as assessed by means of radiographic scales. Motor and cognitive development, respiratory function, and safety were evaluated, as well as the pharmacokinetics and pharmacodynamics of ENB-0040. RESULTS Of the 11 patients recruited, 10 completed 6 months of therapy; 9 completed 1 year. Healing of rickets at 6 months in 9 patients was accompanied by improvement in developmental milestones and pulmonary function. Elevated plasma levels of the TNSALP substrates inorganic pyrophosphate and pyridoxal 5'-phosphate diminished. Increases in serum parathyroid hormone accompanied skeletal healing, often necessitating dietary calcium supplementation. There was no evidence of hypocalcemia, ectopic calcification, or definite drug-related serious adverse events. Low titers of anti-ENB-0040 antibodies developed in four patients, with no evident clinical, biochemical, or autoimmune abnormalities at 48 weeks of treatment. CONCLUSIONS ENB-0040, an enzyme-replacement therapy, was associated with improved findings on skeletal radiographs and improved pulmonary and physical function in infants and young children with life-threatening hypophosphatasia. (Funded by Enobia Pharma and Shriners Hospitals for Children; ClinicalTrials.gov number, NCT00744042.).
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Affiliation(s)
- Michael P Whyte
- Center for Metabolic Bone Disease and Molecular Research, Shriners Hospital for Children, St. Louis, MO 63131, USA.
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Escolar DM, Zimmerman A, Bertorini T, Clemens PR, Connolly AM, Mesa L, Gorni K, Kornberg A, Kolski H, Kuntz N, Nevo Y, Tesi-Rocha C, Nagaraju K, Rayavarapu S, Hache LP, Mayhew JE, Florence J, Hu F, Arrieta A, Henricson E, Leshner RT, Mah JK. Pentoxifylline as a rescue treatment for DMD: a randomized double-blind clinical trial. Neurology 2012; 78:904-13. [PMID: 22402864 DOI: 10.1212/wnl.0b013e31824c46be] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
OBJECTIVE To determine whether pentoxifylline (PTX) slows the decline of muscle strength and function in ambulatory boys with Duchenne muscular dystrophy (DMD). METHODS This was a multicenter, randomized, double-blinded, controlled trial comparing 12 months of daily treatment with PTX or placebo in corticosteroid-treated boys with DMD using a slow-release PTX formulation (~20 mg/kg/day). The primary outcome was the change in mean total quantitative muscle testing (QMT) score. Secondary outcomes included changes in QMT subscales, manual muscle strength, pulmonary function, and timed function tests. Outcomes were compared using Student t tests and a linear mixed-effects model. Adverse events (AEs) were compared using the Fisher exact test. RESULTS A total of 64 boys with DMD with a mean age of 9.9 ± 2.9 years were randomly assigned to PTX or placebo in 11 participating Cooperative International Neuromuscular Research Group centers. There was no significant difference between PTX and the placebo group in total QMT scores (p = 0.14) or in most of the secondary outcomes after a 12-month treatment. The use of PTX was associated with mild to moderate gastrointestinal or hematologic AEs. CONCLUSION The addition of PTX to corticosteroid-treated boys with DMD at a moderate to late ambulatory stage of disease did not improve or halt the deterioration of muscle strength and function over a 12-month study period. CLASSIFICATION OF EVIDENCE This study provides Class I evidence that treatment with PTX does not prevent deterioration in muscle function or strength in corticosteroid-treated boys with DMD.
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Affiliation(s)
- D M Escolar
- Children’s National Medical Center, Washington, DC, USA.
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4
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van der Ploeg AT, Clemens PR, Corzo D, Escolar DM, Florence J, Groeneveld GJ, Herson S, Kishnani PS, Laforet P, Lake SL, Lange DJ, Leshner RT, Mayhew JE, Morgan C, Nozaki K, Park DJ, Pestronk A, Rosenbloom B, Skrinar A, van Capelle CI, van der Beek NA, Wasserstein M, Zivkovic SA. A randomized study of alglucosidase alfa in late-onset Pompe's disease. N Engl J Med 2010; 362:1396-406. [PMID: 20393176 DOI: 10.1056/nejmoa0909859] [Citation(s) in RCA: 481] [Impact Index Per Article: 34.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
BACKGROUND Pompe's disease is a metabolic myopathy caused by a deficiency of acid alpha glucosidase (GAA), an enzyme that degrades lysosomal glycogen. Late-onset Pompe's disease is characterized by progressive muscle weakness and loss of respiratory function, leading to early death. We conducted a randomized, placebo-controlled trial of alglucosidase alfa, a recombinant human GAA, for the treatment of late-onset Pompe's disease. METHODS Ninety patients who were 8 years of age or older, ambulatory, and free of invasive ventilation were randomly assigned to receive biweekly intravenous alglucosidase alfa (20 mg per kilogram of body weight) or placebo for 78 weeks at eight centers in the United States and Europe. The two primary end points were distance walked during a 6-minute walk test and percentage of predicted forced vital capacity (FVC). RESULTS At 78 weeks, the estimated mean changes from baseline in the primary end points favored alglucosidase alfa (an increase of 28.1+/-13.1 m on the 6-minute walk test and an absolute increase of 3.4+/-1.2 percentage points in FVC; P=0.03 and P=0.006, respectively). Similar proportions of patients in the two groups had adverse events, serious adverse events, and infusion-associated reactions; events that occurred only in patients who received the active study drug included anaphylactic reactions and infusion-associated reactions of urticaria, flushing, hyperhidrosis, chest discomfort, vomiting, and increased blood pressure (each of which occurred in 5 to 8% of the patients). CONCLUSIONS In this study population, treatment with alglucosidase alfa was associated with improved walking distance and stabilization of pulmonary function over an 18-month period. (ClinicalTrials.gov number, NCT00158600.)
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Affiliation(s)
- Ans T van der Ploeg
- Department of Pediatrics, Center for Lysosomal and Metabolic Diseases, Erasmus MC University Medical Center, Rotterdam, The Netherlands.
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Buyse GM, Goemans N, Henricson E, Jara A, van den Hauwe M, Leshner R, Florence JM, Mayhew JE, Escolar DM. CINRG pilot trial of oxatomide in steroid-naïve Duchenne muscular dystrophy. Eur J Paediatr Neurol 2007; 11:337-40. [PMID: 17459739 DOI: 10.1016/j.ejpn.2007.02.009] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/13/2006] [Revised: 02/15/2007] [Accepted: 02/15/2007] [Indexed: 11/18/2022]
Abstract
The authors report a pilot open-label two-center therapeutic trial of oxatomide in 14 steroid-naive DMD boys aged 5-10 years. Comparison of linear evolutions between 3 months medication-free lead-in periods and 6 months treatment periods showed no significant differences in quantitative (QMT) and manual (MMT) measurements of muscle strength and timed functional tests. A modest mitigation of strength deterioration over time cannot be excluded.
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Affiliation(s)
- Gunnar M Buyse
- University Hospitals KU Leuven, Leuven, Herestraat 49, B-3000 Leuven, Belgium.
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Mayhew JE, Florence JM, Mayhew TP, Henricson EK, Leshner RT, McCarter RJ, Escolar DM. Reliable surrogate outcome measures in multicenter clinical trials of Duchenne muscular dystrophy. Muscle Nerve 2007; 35:36-42. [PMID: 16969838 DOI: 10.1002/mus.20654] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
We studied the reliability of a series of endpoints in an evaluation of subjects with Duchenne muscular dystrophy (DMD). The endpoints included quantitative muscle tests (QMTs), timed function tests, forced vital capacity (FVC), and manual muscle tests (MMT). Thirty-one ambulatory subjects with DMD (mean age 8.9 years; range 5-16 years) were evaluated at eight sites by 15 newly trained evaluators as a test of interrater reliability of outcome measures. Both total QMT score [intraclass correlation coefficient (ICC) 0.96] and individual QMT assessments (ICC 0.85-0.96) were highly reliable. Forced vital capacity and all timed function tests were also highly reliable (ICC 0.97-0.99). MMT was the least reliable assessment method (ICC 0.61). These data suggest that primary surrogate outcome measures in large multicenter clinical trials in DMD should use QMT, FVC, or time function tests to obtain maximum power and greatest sensitivity.
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Affiliation(s)
- Jill E Mayhew
- Research Center for Genetic Medicine, Children's National Medical Center, 111 Michigan Avenue NW, Washington, DC 20010, USA
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Gias C, Hewson-Stoate N, Jones M, Johnston D, Mayhew JE, Coffey PJ. Retinotopy within rat primary visual cortex using optical imaging. Neuroimage 2005; 24:200-6. [PMID: 15588611 DOI: 10.1016/j.neuroimage.2004.08.015] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2004] [Revised: 06/25/2004] [Accepted: 08/12/2004] [Indexed: 10/26/2022] Open
Abstract
The purpose of this study was to determine the retinotopic organization of rat primary visual cortex (area 17) using optical imaging technology. Stimulating discrete regions of visual space resulted in localised changes in the remitted light during optical imaging of visual cortex in rat. From these localised changes, our results confirm previous electrophysiological studies on the location, size and organization of rat primary visual cortex. Small differences in the cortical magnification factor (CMF) were found between visual field areas with the highest CMF confined to the upper nasal region. No significant CMF differences were found within the horizontal and vertical visual field axes. No secondary visual areas were activated either anterior or medial to area 17 with the pattern stimuli used in the current study. However, there was evidence of activity to upper nasal stimulation on the posterior lateral extrastriate area. The location of area 17 from optical imaging activity was confirmed anatomically using conventional immunohistochemical techniques. This study shows the retinotopic organization of rat primary visual cortex and serves as a precursor before examining animal models of retinal degeneration and the effectiveness of potential therapies to stem retinal disease.
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Affiliation(s)
- C Gias
- Visual Transplantation Research Group, Department of Psychology, University of Sheffield, Western Bank, S10 2TP, Sheffield, United Kingdom.
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Paley M, Mayhew JE, Martindale AJ, McGinley J, Berwick J, Coffey P, Redgrave P, Furness P, Port M, Ham A, Zheng Y, Jones M, Whitby E, van Beek EJ, Wilkinson ID, Darwent G, Griffiths PD. Design and initial evaluation of a low-cost 3-Tesla research system for combined optical and functional MR imaging with interventional capability. J Magn Reson Imaging 2001; 13:87-92. [PMID: 11169808 DOI: 10.1002/1522-2586(200101)13:1<87::aid-jmri1013>3.0.co;2-0] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A 3-Tesla research system has been developed for functional and interventional magnetic resonance imaging (MRI) procedures on animal models based on a low field niche spectrometer. Use of two stages of fourth harmonic frequency multiplication has allowed us to produce a high-frequency spectrometer with good frequency stability based on a low-frequency direct digital synthesizer. The system has been designed with the ability to introduce interventional tools such as biopsy needles, radiofrequency (RF) electrodes, and fiber optics for optical spectroscopy and thermal ablation as well as drug infusions to allow function to be studied in the presence of external challenges. Full MR-compatible physiologic support capability allows animals to be maintained in a stable condition over extended periods of study. Functional MR images have been acquired by using gradient echoes (TR/TE = 40/12 msec) from the rat whisker barrel cortex using electrical stimulation (5-V, 1.5-mA, 1-msec pulses at 5 Hz via two needle electrodes inserted into the rat whisker pad). Initial results using respiratory gas challenges of 100% N(2), 100% O(2), and 10% CO(2) have shown excellent agreement between single wavelength (633 nm) optical and functional MR time series with subsecond time resolution. The 1-mm copper electrodes for interventional radiofrequency ablation procedures were easily visualized in the superior colliculus by using gradient echo sequences. This novel, low-cost, high field system appears to be a useful research tool for functional and interventional studies of rat brain and allows concurrent optical spectroscopy. J. Magn. Reson. Imaging 2001;13:87-92.
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Affiliation(s)
- M Paley
- Section of Academic Radiology and Department of Psychology, University of Sheffield, Royal Hallamshire Hospital, Glossop Road, Sheffield S10 2JF, England.
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Schiessl I, Stetter M, Mayhew JE, McLoughlin N, Lund JS, Obermayer K. Blind signal separation from optical imaging recordings with extended spatial decorrelation. IEEE Trans Biomed Eng 2000; 47:573-7. [PMID: 10851799 DOI: 10.1109/10.841327] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
Optical imaging is the video recording of two-dimensional patterns of changes in light reflectance from cortical tissue evoked by stimulation. We derived a method, extended spatial decorrelation (ESD), that uses second-order statistics in space for separating the intrinsic signals into the stimulus related components and the nonspecific variations. The performance of ESD on model data is compared to independent component analysis algorithms using statistics of fourth and higher order. Robustness against sensor noise is scored. When applied to optical images, ESD separates the stimulus specific signal well from biological noise and artifacts.
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Affiliation(s)
- I Schiessl
- Department of Computer Science, Technical University of Berlin, Germany.
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10
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Affiliation(s)
- D Coca
- Department ACSE, University of Sheffield, United Kingdom
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11
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Mayhew JE, Askew S, Zheng Y, Porrill J, Westby GW, Redgrave P, Rector DM, Harper RM. Cerebral vasomotion: a 0.1-Hz oscillation in reflected light imaging of neural activity. Neuroimage 1996; 4:183-93. [PMID: 9345508 DOI: 10.1006/nimg.1996.0069] [Citation(s) in RCA: 267] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Imaging of scattered and reflected light from the surface of neural structures can reveal the functional architecture within large populations of neurons. These techniques exploit, as one of the principal signal sources, reflectance changes produced by local variation in blood volume and oxygen saturation related to neural activity. We found that a major source of variability in the captured light signal is a pervasive low-frequency (0.1-Hz) oscillation which apparently results from regional cerebral blood flow. This signal is present in brain parenchyma as well as the microvasculature and exhibits many characteristics of the low-frequency "vasomotion" signals observed in peripheral microcirculation. Concurrent measurements in brain with a laser Doppler flow meter contained an almost identical low-frequency signal. The presence of the 0.1-Hz oscillation in the cerebral microcirculation could underlie a portion of the previously described characteristics reported in reflected-light imaging studies. The prevalence of the oscillatory phenomena in the brain raises substantial temporal sampling issues for optical imaging and for other visualization techniques which depend on changes in regional cerebral blood dynamics, such as functional magnetic resonance imaging.
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Affiliation(s)
- J E Mayhew
- Artificial Intelligence Vision Research Unit, University of Sheffield, United Kingdom.
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12
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Abstract
A computational method for calibrating stereo using shape-from-texture is described together with five experiments that tested whether the human visual system implements the method. The experiments all tested the prediction that the perceived size of a step between two planar and slanted real surfaces should be affected by texture slant cues projected on to them that are inconsistent with the disparity cues. The predicted effect was observed but the results could be accounted for by a new phenomenon revealed in control conditions: the perceived size of a step between two slanted planes is in part determined by the size of the slants even when texture and stereo cues are held consistent. We conclude that the hypothesis that human stereo is calibrated by texture is not confirmed.
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Affiliation(s)
- J P Frisby
- AI Vision Research Unit, University of Sheffield, England
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13
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Abstract
The pattern of retinal binocular disparities acquired by a fixating visual system depends on both the depth structure of the scene and the viewing geometry. This paper treats the problem of interpreting the disparity pattern in terms of scene structure without relying on estimates of fixation position from eye movement control and proprioception mechanisms. We propose a sequential decomposition of this interpretation process into disparity correction, which is used to compute three-dimensional structure up to a relief transformation, and disparity normalization, which is used to resolve the relief ambiguity to obtain metric structure. We point out that the disparity normalization stage can often be omitted, since relief transformations preserve important properties such as depth ordering and coplanarity. Based on this framework we analyse three previously proposed computational models of disparity processing; the Mayhew and Longuet-Higgins model, the deformation model and the polar angle disparity model. We show how these models are related, and argue that none of them can account satisfactorily for available psychophysical data. We therefore propose an alternative model, regional disparity correction. Using this model we derive predictions for a number of experiments based on vertical disparity manipulations, and compare them to available experimental data. The paper is concluded with a summary and a discussion of the possible architectures and mechanisms underling stereopsis in the human visual system.
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Affiliation(s)
- J Gårding
- Computational Vision and Active Perception Laboratory, Royal Institute of Technology (KTH), Stockholm, Sweden
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Buckley D, Frisby JP, Mayhew JE. Integration of stereo and texture cues in the formation of discontinuities during three-dimensional surface interpolation. Perception 1989; 18:563-88. [PMID: 2602083 DOI: 10.1068/p180563] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A series of stereograms are presented which demonstrate that texture boundaries can strongly influence the perception of discontinuities between neighbouring three-dimensional (3-D) surfaces portrayed by means of stereo cues. In these demonstration figures, no stereo information is available in the immediate vicinity of the boundary between the two 3-D stereo surfaces because all texture in that region is removed in one eye's view. On the other hand, various forms of texture boundary information are provided in the resulting monocular region. This stimulus paradigm is used to explore the question: what influence does texture boundary information have on the nature of the perceived 3-D surface that is interpolated between two stimulus regions which carry stereo cues? It is shown that if a clear-cut texture boundary is present in the monocular region then this is used by the human visual system to fix the perceived location of 3-D crease and step surface discontinuities between the stereo regions. Collett (1985) explored this issue with a similar methodology and reported weak and unreliable assistance from monocular texture boundaries in helping shape 3-D stereo surface discontinuities. The strong and robust phenomena demonstrated here seem to rely on two main differences between the present stimuli and those of Collett. In the present stimuli, figurally continuous textures containing strong texture boundaries are used, together with a technique for minimising the complications, including binocular rivalry, that arise from the borders of the stimulus regions present in only one half of each stereogram.
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Affiliation(s)
- D Buckley
- Al Vision Research Unit, University of Sheffield, UK
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15
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Bradshaw MF, Frisby JP, Mayhew JE. The recovery of structure from motion: no evidence for a special link with the convergent disparity mechanism. Perception 1987; 16:351-7. [PMID: 3432030 DOI: 10.1068/p160351] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Convergent and divergent stereo mechanisms were compared in their ability to recover structure from motion. Contrary to a recent result reported by Richards and Lieberman, no difference in their performance was found; both mechanisms appeared equally capable of supporting the perception of good structure from motion. Possible reasons for the disparate results are discussed.
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Affiliation(s)
- M F Bradshaw
- Department of Psychology, University of Sheffield, UK
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Abstract
The advantages of solving the stereo correspondence problem by imposing a limit on the magnitude of allowable disparity gradients are examined. It is shown how the imposition of such a limit can provide a suitable balance between the twin requirements of disambiguating power and the ability to deal with a wide range of surfaces. Next, the design of a very simple stereo algorithm called PMF is described. In conjunction with certain other constraints used in many other stereo algorithms, PMF employs a limit on allowable disparity gradients of 1, a value that coincides with that reported for human stereoscopic vision. The excellent performance of PMF is illustrated on a series of natural and artificial stereograms. Finally, the differences between the theoretical justification for the use of disparity gradients for solving the stereo correspondence problems presented in the paper and others that exist in the stereo algorithm literature are discussed.
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Abstract
If the image received by one eye is vertically magnified by a small amount then an illusory tilt is perceived around the vertical axis through the fixation point. This is known as the induced effect and it can be explained by a recent computational theory of binocular vision which treats it as a side-effect of the use of vertical disparities to recover information about the distance to the fixation point and the angle of gaze. We have investigated the consequences of introducing vertical magnifications of some parts of a scene and not others and report here that there is a simple linear relationship between the size of the induced effect and the average vertical magnification. This suggests that a pooling strategy is adopted in the measurement of vertical disparities, a result which fits in well with expectations of the theory.
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Abstract
We point out that the horizontal disparities between a pair of retinal images are inadequate for computing the three-dimensional structure of a scene unless supplemented by independent information about the distance and direction of the fixation point. We suggest that this supplementary information is derived not from non-visual sources, but from the vertical disparities of a few non-meridional image points. This hypothesis is shown to account quantitatively for Ogle's induced effect--the marked distortion of a scene by a vertically magnifying lens placed in front of one eye.
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Abstract
Vergence responses were recorded from practised observers viewing narrow-band spatial-frequency-filtered planar random-dot stereograms. It was found that low spatial frequencies of 1.75-3.5 cycles deg-1 could trigger appropriate vergence responses to larger disparities than could the relatively high spatial frequency of 7.0 cycles deg-1. Nevertheless, appropriate vergence shifts were observed reliably for spatial-frequency/disparity combinations well outside the range predicted by Marr and Poggio's (1979) model of stereo vision. It was also found that for large-disparity/high-spatial-frequency combinations which the subjects could not fuse, the vergence system went into oscillation with the eyes diverging and converging at a frequency of about 1.5 Hz and with an amplitude of about 10-20 min arc. Finally, it was demonstrated that when a prominent monocular cue was superimposed upon a large-disparity/high-spatial-frequency stereogram then a speedy vergence response occurred which resulted in successful fusion. This latter finding supports the hypothesis advanced earlier that monocular cues can facilitate stereopsis by triggering appropriate vergence shifts.
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Frisby JP, Mayhew JE. Spatial frequency tuned channels: implications for structure and function from psychophysical and computational studies of stereopsis. Philos Trans R Soc Lond B Biol Sci 1980; 290:95-116. [PMID: 6106245 DOI: 10.1098/rstb.1980.0085] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Various psychophysical experiments investigating the role of spatial frequency tuned channels in stereopsis are reviewed and a computational model of stereopsis deriving from these studies is described. The distinctive features of the model are: (1) it identifies edge locations in each monocular field by searching for zero crossings in non-orientated centre-surround convolution profiles; (2) it selects among all possible binocular point-for-point combinations of edge locations only those which satisfy a (quasi-) collinear figural grouping rule; (3) it presents a concept of the orientated and spatial frequency tuned channel as a nonlinear grouping operator. The success of the model is demonstrated both on a stereo pair of a natural scene and on a random-dot stereogram.
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Abstract
A computational model is described which effects the binocular combination of monocular edge information. The distinctive features of the model are: (i) it identifies edge locations in each monocular field by searching for zero crossings in nonorientated centre-surround convolution profiles; (ii) it selects amongst all possible binocular point-for-point combinations of edge locations only those which satisfy a (quasi-)collinear figural grouping rule; (iii) it presents a concept of the orientated and spatial-frequency-tuned channel as a nonlinear grouping operator. The success of the model is demonstrated both on a stereo pair of a natural scene and on a random-dot stereogram.
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Abstract
Surfaces possessing steep variations in depth present severe difficulties for orientationally tuned filter models of stereopsis. These difficulties are discussed in connection with a random-dot stereogram depicting a surface with steep horizontal corrugations. As expected on theoretical grounds, we find that a vertical +/- 45 degrees orientationally filtered version of this stereogram cannot be fused. Moreover, it is demonstrated that a horizontal +/- 45 degrees filtered version can be fused only with difficulty and its stereo percept is poor compared to that of the unfiltered original. It is concluded that orientated filters seem ill-designed to mediate the extraction of disparity cues, at least in the cases under consideration.
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Abstract
Various stereoscopic demonstrations are presented which indicate that visual texture discrimination is based on processes which occur after, or at the same time as, the binocular combination of images from the two eyes. Monocularly invisible texture regions can become apparent, and monocularly visible regions can be hidden, by the processes of binocular fusion.
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Abstract
A major theory of early visual processing has recently been proposed by Marr, which considers a number of aspects of visual perception in great detail, including grouping and texture discrimination. New phenomena associated with texture discrimination are described and experiments reported which allow a preliminary comparison of Marr's theory, as it applies to texture discrimination, with more established theories such as that due to Julesz. One experiment produced results which are clearly consistent with Marr's account, but the ability of his theory to deal with additional data on region suppression is not established. The theory of the analysis of proximity relations proposed by Fox offers a broadly satisfactory account of many texture perception results, while relying on the more fundamental parts of Marr's theory of primitive visual processes to deal with the remainder. A further attraction of proximity analysis is that it may shed new light on the classical paradox of symmetry perception. Some ways in which the preliminary proximity analysis model is incomplete are discussed, and it is concluded that development of the model may be profitable for theories of early visual processing.
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Abstract
A series of experiments is reported on rivalrous-texture stereograms composed of narrowband-filtered random noise. Experiment 1 found that the apparent deth-disparity function for such stereograms was different from that observed with similar but nonrivalrous stimuli. In particular, rivalrous divergent disparities produced the same depth as rivalrous zero disparity and this latter disparity itself produced a significant degree of protruding (i.e. 'convergent') depth in a certain type of rivalrous-texture stereogram. Free inspection was permitted and disparities were in the range 16 min convergent to 16 min divergent. Experiment 2 found no convincing evidence for reliable qualitative depth discriminations from tachistoscopic presentations of rivalrous-texture stereograms, using a forced-choice task requiring a discrimination between 16 min convergent and 16 min divergent conditions. This task was solved easily for equivalent nonrivalrous stimuli. Experiment 3 measured a hitherto unreported binocular depth effect, termed 'paradepth', which is produced by presenting a target in one field only. This effect appears to be a genuine biocular depth effect and not just the result of an ordinary monocular masking depth cue. The size of the depth effect was found to be a function of the width of the target. The overall conclusion derived from the series of experiments is that rivalrous-texture stereograms are complex stimuli capable of yielding curious and unexpected depth effects which are not readily explained in detail within any existing theoretical framework.
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Abstract
Contrast thresholds for stereopsis were measured for a variety of bandpass-filtered random-dot stereograms in a series of experiments. The principal finding was that contrast thresholds for stereopsis from 'complex' stereograms composed of mixtures of (a) two widely different spatial frequencies or (b) two or more widely different oriented random textures, are considerably lower than would be expected if stereopsis from such stimuli is mediated by the first component to rise above its own stereopsis contrast threshold. Instead, it appears that stereopsis comes about whenever the supradetection-threshold contrast of a stereogram exceeds a certain level, regardless of whether this contrast is provided by a single component or by a mix of two different ones. The implications of these findings for models of stereopsis are discussed.
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Abstract
A stereopsis signal carried by an oriented random texture and masked by a similar noise texture is not unmasked when the orientation of the noise is rotated. This result is discussed in connection with the orientational tuning of local and global stereopsis processes.
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Abstract
Contrast thresholds for stereopsis from narrow-band-filtered random-dot stereograms were compared with contrast thresholds for simple detection of similar narrow-band noise. Centre frequencies of filters were in the range 2.5--15 cycles deg(-1). It was found that the contrast sensitivity function for stereopsis is similar in shape to that for detection, suggesting that as far as contrast requirements are concerned the mechanisms of global stereopsis do not show a bias in sensitivity to any particular spatial frequency but instead require a constant level of suprathreshold contrast regardless of spatial frequency.
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Abstract
The use of the term 'global in the context of stereopsis is discussed. It is concluded that different meanings of this term need to be kept carefully distinguished at all times. The discussion centres around a series of demonstrations introduced by Ramachandran and Nelson, and interpretations are offered for these demonstrations in terms of spatial-frequency-tuned stereopsis channels.
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Abstract
A microtextured surface such as a homogeneously illuminated tracing-paper screen provides an excellent test surface for the movement aftereffect. When it is moved against the aftereffect at the appropriate velocity, a null occurs and the screen appears stationary. However, if patterned illumination is superimposed on the homogeneous field, the nulling breaks down. The pattern appears to move in one direction, driven by the aftereffect, and the screen can be clearly seen moving in the opposite direction. This breakdown begins to occur at luminances just above threshold for the detection of the pattern. The implication is that two populations of motion detectors are involved. Evidence in support of this postulate is presented.
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Abstract
Sekuler and Ganz (1963) called the difference in luminance threshold for movement in the same direction versus movement in the opposite direction to the adapting motion ‘direction-specific adaptation’ (DSA). The experiments reported here investigate colour-contingent DSA. After exposure of subjects to clockwise motion of a red pattern alternating with counterclockwise motion of a green pattern, their threshold for clockwise motion was found to be greater than for counterclockwise motion when the illumination was red, but lower when the illumination was green.
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Mayhew JE. Directional asymmetry in the duration of simple movement aftereffects produced by movement aftereffects contingent on colour. Perception 1972; 1:453-7. [PMID: 4680945 DOI: 10.1068/p010453] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
Movement aftereffects contingent on colour and pattern (CMAEs) were produced. A pattern, illuminated with red light and rotating clockwise, was alternated with its contrast-reversed ‘negative’, illuminated with green light and rotating counterclockwise. Subsequently, when the stationary patterns were presented, subjects reported counterclockwise MAEs on the ‘red’ pattern, and clockwise MAEs on the ‘green’ pattern. It was found that a simple MAE produced by adapting to the ‘red’ pattern and tested on the ‘green’ pattern was greater in duration when the direction of the inducing motion was opposite to that used in the CMAE adaptation procedure. It is suggested that this directional asymmetry in the duration of the simple MAE may be used as a within-subjects measure of the CMAE.
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