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VISION
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Project 74 - Computational Modelling of Visual Perception
Visual Psychophysics (Watt)
This has comprised work in four main areas:
74.1 Shape Perception
Investigations to discover something of the nature of 2D shape measurement and representation used in human vision produced several findings of note. First, corners and intersections of edges and lines have a priority in visual processing and effectively delimit the spatial extent of integration for smooth shapes even when the smooth line extends across an intersection [588]. Second, the nature of the integration process has also been established [594]. Finally, the limitations on precision have been explored and related to theoretical concepts [607].
74.2 Eccentricity and Peripheral Vision
In a separate enterprise, and in collaboration with Hess and Pointer of the Physiological Laboratory, University of Cambridge, the differences between foveal and peripheral vision have been quantified [573]. There is little evidence for any significant qualitative difference, except that positional uncertainty is very high beyond the central degree or so of vision.
74.3 Time Course of Vision
The most important development concerns the time course of the evolving visual percept. An extensive series of experiments measured the effective spatial scale or resolution of the visual system as a function of time after stimulus presentation [590, 617]. Two distinct functions were obtained. For texture and statistical information there is hardly any effect of exposure duration over and above that anticipated because of the increased signal/noise ratio of the stimulus. For geometric and spatial tasks, on the other hand, the effective spatial scale of the visual system scans from a very coarse level of resolution to increasingly fine degrees in a direct reciprocal relationship with time. The effect lasts for one or two seconds and under some circumstances considerably longer. This work has been related both to a theoretical model of human vision (see below) and also to the various phenomena of visual attention [561]. In particular it has been suggested that many of the "search-light" type of effects can be related to this time course. Whether this is generally true remains to be seen.
74.4 Visual Theory
A major product of Watt's time at the APU was the development of theoretical insight into human vision. His book [561] is a statement of many of the important issues in understanding vision. Its claim is that three different sources of knowledge about human vision, psychophysical, computational theoretic, and cognitive experimental, can be combined to give a single coherent picture of the human visual system as a dynamic process producing refinable, hierarchical representations of the optical image. A mechanism is proposed and the way in which the mechanism could account for many phenomena of visual attention is described.
The essence of the theory is that the computation of spatial position within a metrical framework requires iterative parallel processing and is time consuming. Psychophysical research has identified the mechanisms whereby the effects of this slow process can be alleviated, and the cognitive research can be understood as giving details of how the process can be programmed and controlled.
Project 75 - Visual Discomfort and Environmental Design
A theory of visual discomfort has been developed by Wilkins which can account for the complaints of eye-strain and headache common in the modern office environment. According to the theory outlined in the last progress report but reviewed more recently [596], at least two aspects of particular retinal images (pulsation and "stripes") make the neural computation involved in vision unnecessarily complex, with visual discomfort as a consequence.
75.1 Pulsation of Light (Craven, Neary, Wilkins)
The light from a fluorescent lamp and from a visual display unit (VDU) pulsates at a high frequency. Pulsation of light affects the control of eye movements [621, 210, 597] and accommodation [576] even at high frequencies when the light appears steady. Contours lit briefly during a saccade are not suppressed in the ordinary way but are perceptually confused with those lit afterwards, which may be one reason why corrective saccades are increased in number [577].
Rapid pulsation of light interferes with accommodation [576] and causes headaches and eye-strain. A double-blind study compared conventional fluorescent lighting with that from a new high-frequency circuit that avoids the typical 100-per-second pulsations. The steady lighting was associated with less than half the episodes of headaches and eye-strain [619, 600].
Watts and Wilkins have shown that a substantial proportion of patients with agoraphobia report that fluorescent lighting precipitates their panic attacks [595]. When agoraphobic patients were tested under double-blind conditions, heart rate was higher under conventional pulsating fluorescent lighting than under the high-frequency form [572]. The implications of these findings are far-reaching. Fluorescent lighting is ubiquitous in public places, and if it helps to provoke panic attacks, one possible major factor in agoraphobia has been discovered.
75.2 "Stripes" (Watt, Wilkins)
The visual system seeks to group the detail in the visual image using information in the mid-range spatial frequencies [561]. This grouping becomes computationally complex when the mid-range frequency components are similar and therefore ambiguous with respect to their position. According to the theory of visual discomfort [627], this is why regular geometric patterns of stripes with specific spatial characteristics can provoke eye-strain. The neurological mechanisms responsible for the visual discomfort resemble those that underlie photosensitive epilepsy in so far as they involve an excess of physiological excitation [611, 612]. They differ in that the synchronization of that excitation at a cortical level is necessary for epileptogenesis but not for discomfort [598, 626].
The successive lines of text resemble a pattern of stripes with epileptogenic properties, and this is one reason why reading can provoke seizures, eye-strain and headaches (Wilkins and Nimmo-Smith, 1984, [614, 602]). Some texts are more striped than others, and although this is difficult to discern from the page, it is immediately evident after spatial filtering.
Project 76 - Visual Aspects of Epilepsy and Other Diseases
76.1 Epilepsy (Wilkins)
About 4% of patients with epilepsy are liable to visually-induced seizures. The visual stimulation responsible includes both flickering light and stationary steadily-illuminated patterns, usually of stripes. The seizures start in the visual cortex of one cerebral hemisphere or both hemispheres independently [609]. The seizures occur when normal physiological excitation involves more than a critical cortical area, particularly when the excitation is rhythmic [564].
Studies of pattern sensitivity during the course of therapy with the anticonvulsant drug, sodium valproate, have shown that the drug affects the spread of the EEG discharge but leaves the trigger mechanism relatively unaffected [568].
Certain visual display units share characteristics in common with television (Wilkins, 1984), and television can induce seizures. Details as to which VDUs and televisions present a risk of seizures, and how this risk can be minimised, have been reviewed for the benefit of patients [615] and those who care for them [610, 565]. Non-pharmacological techniques for treating other forms of reflex epilepsy have also been reviewed [614].
Both sensory and cognitive processes can contribute to epileptogenesis, and are in turn disrupted by it [566, 616].
76.2 Headache (Neary, Wilkins, M Williams)
Mechanisms of migraine [624] and the role of visual stimulation in the induction of headache [628] have been reviewed for the benefit of patients.
The illusions observed in patterns with epileptogenic characteristics provide for a test that may be useful in the diagnosis and management of headache. People with visual or ocular involvement in headaches report more illusions when they observe such patterns, and their illusion susceptibility is elevated both on days when a headache occurs [684] and up to 24 hours before a headache [578]. A collaborative project with Khalil and Legge (Hammersmith Hospital) has investigated contrast sensitivity and illusions in patients with classical migraine whose visual aura occurs consistently in one lateral visual field. Illusions are predominant in that field, and contrast sensitivity is poorer.
76.3 Stroke (Wilkins)
In collaboration with G Plant (National Hospital) the spatio-temporal properties of preserved movement sensitivity have been studied in a patient with occipital lobe damage [581]. Various techniques for rehabilitation following occipital strokes have been described, based on neuropsychological principles [604].
76.4 Other Diseases (Wilkins)
A simple clinical test of contrast sensitivity has been developed [625, 563] and marketed [622], and norms for the test have been published [601]. The test concentrates measurements at one spatial frequency, that at which deficits due to disease are most commonly shown. The test has been shown to have diagnostic value in multiple sclerosis [570], optic neuritis [571], diabetes [569] and glaucoma [585].
An alternative contrast sensitivity test in the form of low-contrast letters has also been published in collaboration with Robson and Pelli of the Cambridge Physiology Department [580] and is currently under evaluation.
76.5 Amblyopia (Watt)
An extensive examination of the condition amblyopia was carried out by Watt in collaboration with Hess, Physiological Laboratory, University of Cambridge [592, 616, 605]. Their finding was that in anisometropic amblyopia, the bad eye behaves exactly as would be expected if the connections between optic nerve and, say, visual cortex were mildly scrambled. No other difference was found. The most likely conclusion is that the optic nerve makes only approximately topologically correct connections with the brain and that these are "unscrambled" during development. The key to doing this lies in the way in which, for a sharply focussed image, near points will have highly correlated patterns of response, whereas far points will be uncorrelated.
The pattern of results in strabismic amblyopia is much more complex, and this work has not yet been concluded.
Watt also collaborated with Cowell in a study of a larger sample of patients presenting at the eye clinic of Leicester Royal Infirmary. Using a purpose-designed test chart, the above findings on anisometropic amblyopia have been replicated on 50 patients aged 5-10 years. A longitudinal study, with and without patching of the good eye (the presently preferred treatment) is being considered.
REFERENCES
Al - Authored Books
561. WATT, R.J. (1988) Visual Processing: Computational, Psychophysical and Cognitive Research. Hove: Lawrence Erlbaum Associates.
B - Refereed Journal Articles
562. BARTON, J. and WATT, R. (1988) An Electronic Oscilloscope Spot Diffuser for measuring neural blur. Clinical Vision Sciences, 3, 289-291.
563. Bertoni, G., Somazzi, L., Blini, M., Delia Sala, S. and WILKINS, A. (1986) La sensibilite au contraste par un nouveau test a choix force. Bull, el Mem S.F.O., 97, 140-145.
564. Binnie, C.D., Findlay, J. and WILKINS, A.J. (1985) Mechanisms of epileptogenesis in photosensitive epilepsy implied by the effects of moving patterns. Electroencephalography and Clinical Neurophysiology, 61, 1-6.
565. Binnie, C.D., Kasteleijn-Nolst Trenite, D.G.A., de Korte, R. and WILKINS, A.J. (1985) Visual display units and risk of seizures. The Lancet, 8435, p.991.
566. Binnie, C.D., Kasteleijn-Nolst Trenite, D.G.A., Smit, A.M. and WILKINS, A.J. (1987) Interactions of epileptiform EEG discharges and cognition. Epilepsy Research, 1, 239-245.
567. CRAVEN, B.J. and WATT, R.J. The use of fractal image statistics in the estimation of spatial extent. Spatial Vision, in press.
568. Darby, C.E., Park, D.M., Smith, A.T. and WILKINS, A.J. (1986) EEG characteristics of epileptic pattern sensitivity and their relation to the nature of pattern stimulation and the effects of sodium valproate. Electroencephalography and Clinical Neurophysiology, 63, 517-525.
569. Delia Sala, S., Bertoni, G., Somazzi, L., Stubbe, F. and WILKINS, A.J. (1985) Impaired contrast sensitivity in diabetic patients with and without retinopathy: A new technique for rapid assessment. British Journal of Ophthalmology, 69, 136-142.
570. Delia Sala, S., Comi, G., Martinelli, V., Somazzi, L. and WILKINS, A.J. (1987) The rapid assessment of visual dysfunction in multiple sclerosis. Journal of Neurology, Neurosurgery, and Psychiatry, 50, 840-846.
571. Delia Sala, S., Somazzi, L. and WILKINS, A.J. (1985) Rapid technique for detecting "blurred vision" in diseases of primary visual pathways. The Lancet, 2, (8462), 1015-1016.
572. Hazell, J. and WILKINS, A.J. A contribution of fluorescent lighting to agoraphobia. Psychological Medicine, in press.
573. Hess, R.F., Pointer, J.S. and WATT, R.J. (1989) How are spatial filters used in fovea and para fovea? Journal of the Optical Society of America A, 6, 329-339.
574. MCKENNA, F.P. (1985) Another look at the 'New Psychophysics'. British Journal of Psychology, 76, 97-109.
575. MCKENNA, F.P. (1985) Modifying the gestalt factor of proximity: Theories compared. Perception, 14, 359-366.
576. NEARY, C. (1989) The effect of high frequency flicker on accommodation. Ophthalmic and Physiological Optics, 9, 440-446.
577. NEARY, C. and WILKINS, A.J. (1989) Effect of phosphor persistence on perception and the control of eye movements. Perception, 18, 257-264.
578. NEARY, C. and WILKINS, A.J. A study of visual function in patients wearing tinted glasses. (Manuscript in preparation).
579. NEARY, C, WILKINS, A.J. and WILLIAMS, J.M.G. Mood and pattern sensitivity in headache sufferers: A longitudinal study. (Manuscript submitted).
580. Pelli, D.G., Robson, J.G. and WILKINS, A.J. (1988) The design of a new letter chart for measuring contrast sensitivity. Clinical Vision Sciences, 2, 187-199.
581. Plant, G.T. and WILKINS, A.J. (1988) Preserved movement sensitivity following occipital lobe damage: A case report of spatio-temporal contrast sensitivity in the Riddoch phenomenon. Clinical Vision Sciences, 2, 321-329.
582. Pointer, J. and WATT, R.J. (1987) Shape recognition in amblyopia. Vision Research, 27, 651-660.
583. POULTON, E.C. (1985) Geometric illusions in reading graphs. Perception and Psychophysics, 37, 543-548.
584. POULTON, E.C. and SIMMONDS, D.C.V. (1985) Subjective zeros, subjectively equal stimulus spacing, and contraction biases in very first judgments of lightness. Perception and Psychophysics, 37, 420-428.
585. Somazzi, L., Delia Sala, S. and WILKINS, A.J. A simple test of contrast sensitivity in glaucoma. Italian Journal of Ophthalmology, in press.
586. WATT, R. (1985) Image segmentation at contour intersections in human focal vision. Journal of the Optical Society of America, 2, (7 July 1985), 1200-1204.
587. WATT, R.J. (1985) Structured representations in low-level vision. Nature, 313, 266-267.
588. WATT, R.J. (1986) Feature-based image segmentation in human vision. Spatial Vision, 1, 243-256.
589. WATT, R.J. (1987) An outline of the primal sketch in human vision. Pattern Recognition Letters, 5, 139-150.
590. WATT, R.J. (1987) Scanning from coarse to fine spatial scales in the human visual system after the onset of a stimulus. Journal of the Optical Society of America A, 4, 2006-2021.
591. WATT, R.J. and Campbell, F.W. (1985) Vernier acuity: Interactions between length effects and gaps when orientation cues are eliminated. Spatial Vision, 1, 31-38.
592. WATT, R.J. and Hess, R.F. (1987) Spatial information and uncertainty in anisometropic amblyopia. Vision Research, 27, 661-674.
593. WATT, R. and Morgan, M. (1985) A theory of the primitive spatial code in human vision. Vision Research, 25, 1661-1674.
594. WATT, R.J., Ward, R.M. and Casco, C. (1987) The detection of deviation from straightness in lines. Vision Research, 27, 1659-1678.
595. WATTS, F.N. and WILKINS, A.J. (1989) The role of provocative visual stimuli in agoraphobia. Psychological Medicine, 19, 875-885.
596. WILKINS, A.J. (1985) Discomfort and visual displays. Displays, April, 101- 103.
597. WILKINS, A. (1986) Intermittent illumination from visual display units and fluorescent lighting affects movements of the eyes across text. Human Factors, 28, 75-81.
598. WILKINS, A.J. (1986) What is visual discomfort? Trends in Neurosciences, 9, 343-346.
599. WILKINS, A.J. (1987) What's in a name? Perception, 16, 409-410.
600. WILKINS, A.J. (1988) Visual distress in the office environment. Facilities, 6,9-12.
601. WILKINS, A.J., Delia Sala, S., Somazzi, L. and NIMMO-SMITH, I. (1988) Age-related norms for the Cambridge Low Contrast Gratings, including details concerning their design and use. Clinical Vision Sciences, 2, 201-212.
602. WILKINS, A.J. and NIMMO-SMITH, I. (1987) The clarity and comfort of printed text. Ergonomics, 30, 1705-1720.
603. WILKINS, A.J., NIMMO-SMITH, I., Slater, A.I. and Bedocs, L. (1989) Fluorescent lighting, headaches and eyestrain. Lighting Research and Technology, 21, 11-18.
604. WILKINS, A.J., Plant, G. and Huddy, A. (1989) Neuro-psychological principles applied to rehabilitation of a stroke patient. The Lancet, 1, (8628), p.54.
C - Invited Chapters and Commentaries
605. Hess, R.F., Field, D.J. and WATT, R.J. The puzzle of amblyopia. In C. Blakemore (Ed.), Efficiency and Coding in Vision. Cambridge: Cambridge University Press, in press.
606. WATT, R.J. (1988) What is Weber's Law? Behavioral and Brain Sciences, 12,313-314.
607. WATT, R.J. and NIMMO-SMITH, I. Representing the shape of image contours. In J-C. Simon (Ed.), From the Pixels to the Features. North-Holland, in press.
608. WATT, R.J. and Rogers, B.J. (1989) Human vision and cognitive science. In A.D. Baddeley and N.O. Bernsen (Eds.), Research Directions in Cognitive Science: A European Perspective, Vol. 1: Cognitive Psychology. London: Lawrence Erlbaum Associates, pp.9-22.
609. WILKINS, A.J. (1986) Disturbances of vision and their association with epilepsy and related disorders. In M.R. Trimble and E.H. Reynolds (Eds.), What is Epilepsy? The Clinical and Scientific Basis of Epilepsy. Edinburgh: Churchill Livingston, pp.183-191.
610. WILKINS, A.J. (1987) Photosensitive epilepsy and visual display units. In E. Ross, D. Chadwick and R. Crawford (Eds.), Epilepsy in Young People. Chichester: John Wiley and Sons Ltd., pp.147-155.
611. WILKINS, A.J. (1987) Visual sensitivity and hyperexcitability in epilepsy and migraine. In F. Andermann and E. Lugaresi (Eds.), Migraine and Epilepsy. Boston, MA: Butterworth Publishers, pp.339-365.
612. WILKINS, A.J. (1989) Photosensitive epilepsy and visual discomfort. In C. Kennard and M. Swash (Eds.), Hierarchies in Neurology: A Reappraisal of a Jacksonian Concept. London: Springer-Verlag, pp.65-75.
613. WILKINS, A.J. and CRAVEN, B.J. (1987) Visual display units and fluorescent lighting enlarge movements of the eyes across text. In J. Crowly-Dillon, E.S. Rosen and J. Marshall (Eds.), Hazards of Light (Eye and Skin): Myths and Realities. Pergamon Press, pp.229-234.
614. WILKINS, A. and Lindsay, J. (1985) Common forms of reflex epilepsy: Physiological mechanisms and techniques for treatment. In T.A. Pedley and B.S. Meldrum (Eds.), Recent Advances in Epilepsy II. Edinburgh: Churchill Livingstone, pp.239-271.
615. WILKINS, A.J. and Lindsay, J. (1987) Questions and answers about photosensitive epilepsy. In E. Ross, D. Chadwick and R. Crawford (Eds.), Epilepsy in Young People. Chichester: John Wiley and Sons, pp.157-160.
D - Conference Proceedings
616. Hess, R. and WATT, R.J. (1987) Human amblyopia: Cortical neurones are misplaced not lost. Journal of Physiology, 390, p.21.
617. WATT, R.J. (1987) Space-scale analysis in the human primal sketch. In Proceedings Alvey Vision Club Conference AVCC87.
618. WILKINS, A.J. (1986) On the manner in which sensory and cognitive processes contribute to epileptogenesis and are disrupted by it. Acta Neurologica Scandanavia, 74, (Suppl.109) (Proceedings of the Fourth Workshop on Memory Function), 91-95.
619. WILKINS, A.J., NIMMO-SMITH, I., Slater, A.I. and Bedocs, L. (1988) Fluorescent lighting, headaches and eye-strain. In Proceedings of the National Lighting Conference and Daylighting Colloquium, Robinson College, Cambridge. CIBSE, pp.188-196.
E - Technical Reports, Theses and Tests
620. CRAVEN, B. (1988) Saccadic undershoot and the estimation of lateral spatial extent. Unpublished PhD Thesis, University of Cambridge.
621. WILKINS, A.J. (1985) Visual display units and fluorescent lighting affect movements of the eyes across text. Human Factors Laboratory of IBM UK Limited, Report HF104 - April.
622. WILKINS, A.J. and Robson, J.G. (1986) Cambridge Low Contrast Gratings. London: Clement Clark International Ltd.
F - Dissemination
623. Gregory, R.L. and WATT, R.J. (1987) Neural channels. In R.L. Gregory (Ed.), Oxford Companion to the Mind. Oxford: Oxford University Press, pp.129-130.
624. Kennard, C. and WILKINS, A.J. (1987) Migraine. In R.L. Gregory (Ed.), Oxford Companion to the Mind. Oxford: Oxford University Press, pp.483-484.
625. WILKINS, A. (1986) Contrast sensitivity and its measurement. Optician, 192, (5054), 13-14.
626. WILKINS, A. (1986) Visual discomfort. Optician, 191, (5048), 15-16.
627. WILKINS, A.J. (1986) Why are some things unpleasant to look at? In D.J. Oborne (Ed.), Contemporary Ergonomics. London: Taylor and Francis, pp.259-263.
628. WILKINS, A. (1987) Stricken by stripes. Migraine News, 53, 8-9. (Also appeared in Migraene Nyt, 1, (87-88), 2-5 (1988) in Dutch.)
Other sections in the 1985-1989 report
3. LANGUAGE, SPEECH, READING AND WRITING