The statistical characteristics of visual images that provoke discomfort generally differ from th... more The statistical characteristics of visual images that provoke discomfort generally differ from those of images found in nature. Computational models of the cortex suggest that uncomfortable images are processed inefficiently, a suggestion consistent with the large electrical and haemodynamic cortical response such images induce. The response is greater in individuals who customarily experience visual discomfort, such as those with migraine. Text provides an unnatural image and can be uncomfortable when small and closely spaced. It can provoke illusions of color, shape and motion, just as do patterns of stripes, and these illusions can disturb reading and reading acquisition. Changing the lighting chromaticity can sometimes reduce these illusions, particularly in patients with migraine aura, thereby facilitating reading.
Migraine is a common neurological disorder characterized by recurrent episodes of headache, frequ... more Migraine is a common neurological disorder characterized by recurrent episodes of headache, frequently accompanied by various reversible neurological disturbances. Some migraine patients experience visually triggered migraine headache, and most attacks of migraine with aura are associated with the disturbance of vision and photophobia, suggesting an abnormal neural activity in the visual cortex. Numerous studies have shown a large cortical hemodynamic response to visual stimulation and an altered intrinsic visual functional connectivity network in patients with migraine. In this interictal study, we applied a novel data-driven method with fMRI to identify the functional network in the visual cortex evoked by visual stimulation and investigated the effect of migraine on this network. We found that the distribution of the functional network along both the ventral and dorsal visual pathways differed between migraine patients and non-headache healthy control participants, providing evid...
lthough the FL-41 lens was originally designed to reduce flicker, it rarely does so now because o... more lthough the FL-41 lens was originally designed to reduce flicker, it rarely does so now because of changes in lamp and driver technology. If it continues to be effective in reducing photophobia it may be for reasons that are complex and relate to cortical excitability.
Photophobia is a complex disorder that can involve aversion not simply to bright light but to spa... more Photophobia is a complex disorder that can involve aversion not simply to bright light but to spatial patterns, colour and flicker. The use of tinted lenses to reduce photophobia in neurological diseases has a long history. Rarely has the possibility that different individuals might require lenses individually tailored to their needs been considered. Here we explore this possibility using the Intuitive Colorimeter system. The colorimeter illuminates text with coloured light and permits the colour, strength of colour and brightness to be manipulated separately. Many individuals find that a colour other than white is comfortable for viewing text. This colour is optimized in the colorimeter by a search strategy that allows for colour adaptation. Spectacle lenses are then individually tinted so that the chosen colour is experienced under conventional lighting. In this article, we review the use of the Intuitive Colorimeter in photosensitive epilepsy, autism, migraine, cluster headache, ...
Background: Trypophobia is a common condition in which sufferers are averse to images of small ho... more Background: Trypophobia is a common condition in which sufferers are averse to images of small holes arranged in clusters. Methods: We used photo-plethysmography to examine cardiovascular correlates and near infrared spectroscopy to examine cortical correlates of the phenomenon in order to validate the Trypophobia Questionnaire and explore the several interlinked explanations of the disorder. Results: Trypophobic images were found to increase heart rate and heart rate variability, but only in individuals with high scores on the Trypophobia Questionnaire. Trypophobic images were also found to elicit larger haemodynamic responses in posterior cortical areas, but again only in individuals with high scores. Limitations: The results are consistent with a contribution from both parasympathetic and sympathetic systems. Conclusion: The data demonstrate the validity of the Trypophobia Questionnaire and show an involvement not only of the autonomic system but cortical mechanisms including cortical hyperexcitability.
e report on a patient with cluster headache who wore spectacles tinted to provide maximum comfort... more e report on a patient with cluster headache who wore spectacles tinted to provide maximum comfort when reading printed text. The spectacles absorbed short-wavelength light and were only worn during the prodrome period. The patient has been free of cluster headaches for the 6 years since the spectacles became available, and the prodromes have decreased in severity and frequency. The hypothalamus is highly active during cluster headaches and receives visual input from the intrinsically photosensitive retinal ganglion cells (ipRGCs). The ipRGCs are most sensitive to short-wavelength light.
Visual discomfort is related to the statistical regularity of visual images. The contribution of ... more Visual discomfort is related to the statistical regularity of visual images. The contribution of luminance contrast to visual discomfort is well understood and can be framed in terms of a theory of efficient coding of natural stimuli, and linked to metabolic demand. While color is important in our interaction with nature, the effect of color on visual discomfort has received less attention. In this study, we build on the established association between visual discomfort and differences in chromaticity across space. We average the local differences in chromaticity in an image and show that this average is a good predictor of visual discomfort from the image. It accounts for part of the variance left unexplained by variations in luminance. We show that the local chromaticity difference in uncomfortable stimuli is high compared to that typical in natural scenes, except in particular infrequent conditions such as the arrangement of colorful fruits against foliage. Overall, our study dis...
Photosensitive epilepsy is interesting partly because it is the most common form of reflex epilep... more Photosensitive epilepsy is interesting partly because it is the most common form of reflex epilepsy, and the discovery of techniques for preventing seizures may be of practical significance, and partly because the visual system is better understood than other sensory systems, and inferences about physiological mechanisms can therefore be made. As will be shown in this chapter, the inferences may help explain not only seizures but also the visual discomfort experienced by people who do not have epilepsy.
Discussion Ratings of discomfort increased with the colour difference (delta E*) between the bars... more Discussion Ratings of discomfort increased with the colour difference (delta E*) between the bars of the gratings, but accommodative lag remained unchanged. Those observers who were sensitive to patterns had a greater accommodative lag. Although it is unlikely that the discomfort from the gratings is caused by poor accommodation, the accommodative system differs from one individual to another systematically to reflect pattern sensitivity, possibly via cortical mechanisms.
The purpose of the study was to assess the repeatability of clinical assessments with the Intuiti... more The purpose of the study was to assess the repeatability of clinical assessments with the Intuitive Colorimeter, a repeatability classified as “poor” in a previous study. Patients underwent assessments with the Intuitive Colorimeter in two studies. In each study, one published by Suttle et al [1] and the other described herein, assessments were undertaken on two occasions. The studies differ in respect of the models of colorimeter used, the methods employed, the interval between examinations, and the masking of examiners. The repeatability was assessed using the methods currently used in clinical practice, which differ according to examiner. Both studies show a similar repeatability of the assessments. This repeatability is consistent with previous literature. We estimate the standard deviation of u’ and v’ coordinates each to be 0.020 and thereby obtain an estimate of the number of tinted trial lenses necessary when prescribing coloured filters. In patients with visual stress asses...
Visual patterns are all around us. Despite overwhelming evidence from the visual sciences that so... more Visual patterns are all around us. Despite overwhelming evidence from the visual sciences that some visual patterns, in particular highly geometric and repetitive patterns, can be aversive, patterns in our visual environment are rarely considered with regard to their impact on brain, behaviour, and well-being. Yet, attempts toward developing healthier, more inclusive cities recently attracted negative headlines, for example for their use of dazzling floor patterns in public spaces that lead to discomfort, avoidance behaviours and falls, particularly in older citizens. Recent developments in analysis now allow us to measure and predict adverse effects of patterns in the real world. Here, we show that aversive patterns are rare in natural scenes but prevalent in modern man-made settings. They occur at every spatial scale, partly because of modular construction, partly because of artistic expression. We review the evidence that visual discomfort and other adverse neurological and behav...
Photophobia is one of the most common symptoms in migraine, and the underlying mechanism is uncer... more Photophobia is one of the most common symptoms in migraine, and the underlying mechanism is uncertain. The discovery of the intrinsically-photosensitive retinal ganglion cells which signal the intensity of light on the retina has led to discussion of their role in the pathogenesis of photophobia. In the current review, we discuss the relationship between pain and discomfort leading to light aversion (traditional photophobia) and discomfort from flicker, patterns, and colour that are also common in migraine and cannot be explained solely by the activity of intrinsically-photosensitive retinal ganglion cells. We argue that, at least in migraine, a cortical mechanism provides a parsimonious explanation for discomfort from all forms of visual stimulation, and that the traditional definition of photophobia as pain in response to light may be too restrictive. Future investigation that directly compares the retinal and cortical contributions to photophobia in migraine with that in other co...
Uncomfortable images generally have a particular spatial structure, which deviates from a recipro... more Uncomfortable images generally have a particular spatial structure, which deviates from a reciprocal relationship between amplitude and spatial frequency (f) in the Fourier domain (1/f). Although flickering patterns with similar temporal structure also appear uncomfortable, the discomfort is affected by not only the amplitude spectrum but also the phase spectrum. Here we examined how discomfort from flicker with differing temporal profiles also varies as a function of the mean light level and luminance contrast of the stimulus. Participants were asked to rate discomfort for a 17° flickering uniform field at different light levels from scotopic to photopic. The flicker waveform was varied with a square wave or random phase spectrum and filtered by modulating the slope of the amplitude spectrum relative to 1/f. At photopic levels, the 1/f square wave flicker appeared most comfortable, whereas the discomfort from the random flicker increased monotonically when the slope of the amplitude spectrum was shallow. This special status for the 1/f square wave condition was limited to photopic light levels. At the lower mesopic or scotopic levels, the effect of phase spectrum on the discomfort was diminished, with both phase spectra showing a monotonic change with the slope of the amplitude spectrum. We show that these changes cannot be accounted for by changes in the effective luminance contrast of the stimuli or
Visual discomfort refers to discomfort or pain in or around the eyes, often associated with heada... more Visual discomfort refers to discomfort or pain in or around the eyes, often associated with headache and/or nausea, and sometimes accompanied by signs such as red, itchy or watering eyes. The lighting conditions likely to cause visual discomfort are insufficient light for the task at hand, dramatic differences in illuminance around the task, shadows, veiling reflections, glare and flicker. To date, research on visual discomfort has been largely reactive, i.e. in response to complaints, but there is now proactive work that explores why discomfort occurs. The hypothesis underlying this work is that the human visual system has evolved to extract information from the natural world efficiently so that when the visual environment departs from the temporal, spatial or chromatic characteristics of the natural world, discomfort is likely because of inefficient neural processing. An important implication is that visual discomfort therefore depends on both the lighting and the dé cor of a space. Until this approach becomes more established, visual discomfort can be minimised by following carefully developed standards and guidance, by using products that meet appropriate standards, by paying attention to both lighting and dé cor and by being aware of the wide variation in individual sensitivity.
Kannada, one of the Dravidian languages, is the official language of Karnataka state of India. Th... more Kannada, one of the Dravidian languages, is the official language of Karnataka state of India. There is a need for a test using Kannada words that can assess visual aspects of reading independently of syntactic and semantic knowledge. A test of reading rate in Kannada was developed following the design principles of the Wilkins Rate of Reading Test (RRT). Fifteen high-frequency bisyllabic Kannada words were selected. Children were recruited from state and private schools that used Kannada or English as the medium of instruction. A total of 799 children from Grade 2 to 9 participated in the study. Reading rate was measured using the English RRT and the Kannada version twice in immediate succession during the first session. In 85 children, measurements using the Kannada RRT were repeated after an interval of 15 days. Pearson product moment correlation between the two immediately successive tests was 0.95 for the Kannada RRT and 0.91 for the English RRT. The correlation for the tests s...
222 SU-PM* BrainVISA: an extensible software environment for sharing multimodal neuroimaging data... more 222 SU-PM* BrainVISA: an extensible software environment for sharing multimodal neuroimaging data and (O-F2) processing tools,
Visual discomfort occurs when the statistics of the retinal image depart from those of natural sc... more Visual discomfort occurs when the statistics of the retinal image depart from those of natural scenes, particularly in respect of an excess energy at spatial frequencies close to 3 cycles/degree. Computer models suggest that uncomfortable stimuli are processed with a larger and less sparse neural response. Uncomfortable stimuli usually evoke a relatively large oxygenation of the visual cortex of the brain, consistent with inefficient neural encoding. The discomfort may be homeostatic. The neural computation that sustains sight is therefore likely to be more complex when the visual scene is spatially periodic, when the colour contrast is high or when saccadic suppression is impaired by flicker that is too rapid to be seen.
The statistical characteristics of visual images that provoke discomfort generally differ from th... more The statistical characteristics of visual images that provoke discomfort generally differ from those of images found in nature. Computational models of the cortex suggest that uncomfortable images are processed inefficiently, a suggestion consistent with the large electrical and haemodynamic cortical response such images induce. The response is greater in individuals who customarily experience visual discomfort, such as those with migraine. Text provides an unnatural image and can be uncomfortable when small and closely spaced. It can provoke illusions of color, shape and motion, just as do patterns of stripes, and these illusions can disturb reading and reading acquisition. Changing the lighting chromaticity can sometimes reduce these illusions, particularly in patients with migraine aura, thereby facilitating reading.
Migraine is a common neurological disorder characterized by recurrent episodes of headache, frequ... more Migraine is a common neurological disorder characterized by recurrent episodes of headache, frequently accompanied by various reversible neurological disturbances. Some migraine patients experience visually triggered migraine headache, and most attacks of migraine with aura are associated with the disturbance of vision and photophobia, suggesting an abnormal neural activity in the visual cortex. Numerous studies have shown a large cortical hemodynamic response to visual stimulation and an altered intrinsic visual functional connectivity network in patients with migraine. In this interictal study, we applied a novel data-driven method with fMRI to identify the functional network in the visual cortex evoked by visual stimulation and investigated the effect of migraine on this network. We found that the distribution of the functional network along both the ventral and dorsal visual pathways differed between migraine patients and non-headache healthy control participants, providing evid...
lthough the FL-41 lens was originally designed to reduce flicker, it rarely does so now because o... more lthough the FL-41 lens was originally designed to reduce flicker, it rarely does so now because of changes in lamp and driver technology. If it continues to be effective in reducing photophobia it may be for reasons that are complex and relate to cortical excitability.
Photophobia is a complex disorder that can involve aversion not simply to bright light but to spa... more Photophobia is a complex disorder that can involve aversion not simply to bright light but to spatial patterns, colour and flicker. The use of tinted lenses to reduce photophobia in neurological diseases has a long history. Rarely has the possibility that different individuals might require lenses individually tailored to their needs been considered. Here we explore this possibility using the Intuitive Colorimeter system. The colorimeter illuminates text with coloured light and permits the colour, strength of colour and brightness to be manipulated separately. Many individuals find that a colour other than white is comfortable for viewing text. This colour is optimized in the colorimeter by a search strategy that allows for colour adaptation. Spectacle lenses are then individually tinted so that the chosen colour is experienced under conventional lighting. In this article, we review the use of the Intuitive Colorimeter in photosensitive epilepsy, autism, migraine, cluster headache, ...
Background: Trypophobia is a common condition in which sufferers are averse to images of small ho... more Background: Trypophobia is a common condition in which sufferers are averse to images of small holes arranged in clusters. Methods: We used photo-plethysmography to examine cardiovascular correlates and near infrared spectroscopy to examine cortical correlates of the phenomenon in order to validate the Trypophobia Questionnaire and explore the several interlinked explanations of the disorder. Results: Trypophobic images were found to increase heart rate and heart rate variability, but only in individuals with high scores on the Trypophobia Questionnaire. Trypophobic images were also found to elicit larger haemodynamic responses in posterior cortical areas, but again only in individuals with high scores. Limitations: The results are consistent with a contribution from both parasympathetic and sympathetic systems. Conclusion: The data demonstrate the validity of the Trypophobia Questionnaire and show an involvement not only of the autonomic system but cortical mechanisms including cortical hyperexcitability.
e report on a patient with cluster headache who wore spectacles tinted to provide maximum comfort... more e report on a patient with cluster headache who wore spectacles tinted to provide maximum comfort when reading printed text. The spectacles absorbed short-wavelength light and were only worn during the prodrome period. The patient has been free of cluster headaches for the 6 years since the spectacles became available, and the prodromes have decreased in severity and frequency. The hypothalamus is highly active during cluster headaches and receives visual input from the intrinsically photosensitive retinal ganglion cells (ipRGCs). The ipRGCs are most sensitive to short-wavelength light.
Visual discomfort is related to the statistical regularity of visual images. The contribution of ... more Visual discomfort is related to the statistical regularity of visual images. The contribution of luminance contrast to visual discomfort is well understood and can be framed in terms of a theory of efficient coding of natural stimuli, and linked to metabolic demand. While color is important in our interaction with nature, the effect of color on visual discomfort has received less attention. In this study, we build on the established association between visual discomfort and differences in chromaticity across space. We average the local differences in chromaticity in an image and show that this average is a good predictor of visual discomfort from the image. It accounts for part of the variance left unexplained by variations in luminance. We show that the local chromaticity difference in uncomfortable stimuli is high compared to that typical in natural scenes, except in particular infrequent conditions such as the arrangement of colorful fruits against foliage. Overall, our study dis...
Photosensitive epilepsy is interesting partly because it is the most common form of reflex epilep... more Photosensitive epilepsy is interesting partly because it is the most common form of reflex epilepsy, and the discovery of techniques for preventing seizures may be of practical significance, and partly because the visual system is better understood than other sensory systems, and inferences about physiological mechanisms can therefore be made. As will be shown in this chapter, the inferences may help explain not only seizures but also the visual discomfort experienced by people who do not have epilepsy.
Discussion Ratings of discomfort increased with the colour difference (delta E*) between the bars... more Discussion Ratings of discomfort increased with the colour difference (delta E*) between the bars of the gratings, but accommodative lag remained unchanged. Those observers who were sensitive to patterns had a greater accommodative lag. Although it is unlikely that the discomfort from the gratings is caused by poor accommodation, the accommodative system differs from one individual to another systematically to reflect pattern sensitivity, possibly via cortical mechanisms.
The purpose of the study was to assess the repeatability of clinical assessments with the Intuiti... more The purpose of the study was to assess the repeatability of clinical assessments with the Intuitive Colorimeter, a repeatability classified as “poor” in a previous study. Patients underwent assessments with the Intuitive Colorimeter in two studies. In each study, one published by Suttle et al [1] and the other described herein, assessments were undertaken on two occasions. The studies differ in respect of the models of colorimeter used, the methods employed, the interval between examinations, and the masking of examiners. The repeatability was assessed using the methods currently used in clinical practice, which differ according to examiner. Both studies show a similar repeatability of the assessments. This repeatability is consistent with previous literature. We estimate the standard deviation of u’ and v’ coordinates each to be 0.020 and thereby obtain an estimate of the number of tinted trial lenses necessary when prescribing coloured filters. In patients with visual stress asses...
Visual patterns are all around us. Despite overwhelming evidence from the visual sciences that so... more Visual patterns are all around us. Despite overwhelming evidence from the visual sciences that some visual patterns, in particular highly geometric and repetitive patterns, can be aversive, patterns in our visual environment are rarely considered with regard to their impact on brain, behaviour, and well-being. Yet, attempts toward developing healthier, more inclusive cities recently attracted negative headlines, for example for their use of dazzling floor patterns in public spaces that lead to discomfort, avoidance behaviours and falls, particularly in older citizens. Recent developments in analysis now allow us to measure and predict adverse effects of patterns in the real world. Here, we show that aversive patterns are rare in natural scenes but prevalent in modern man-made settings. They occur at every spatial scale, partly because of modular construction, partly because of artistic expression. We review the evidence that visual discomfort and other adverse neurological and behav...
Photophobia is one of the most common symptoms in migraine, and the underlying mechanism is uncer... more Photophobia is one of the most common symptoms in migraine, and the underlying mechanism is uncertain. The discovery of the intrinsically-photosensitive retinal ganglion cells which signal the intensity of light on the retina has led to discussion of their role in the pathogenesis of photophobia. In the current review, we discuss the relationship between pain and discomfort leading to light aversion (traditional photophobia) and discomfort from flicker, patterns, and colour that are also common in migraine and cannot be explained solely by the activity of intrinsically-photosensitive retinal ganglion cells. We argue that, at least in migraine, a cortical mechanism provides a parsimonious explanation for discomfort from all forms of visual stimulation, and that the traditional definition of photophobia as pain in response to light may be too restrictive. Future investigation that directly compares the retinal and cortical contributions to photophobia in migraine with that in other co...
Uncomfortable images generally have a particular spatial structure, which deviates from a recipro... more Uncomfortable images generally have a particular spatial structure, which deviates from a reciprocal relationship between amplitude and spatial frequency (f) in the Fourier domain (1/f). Although flickering patterns with similar temporal structure also appear uncomfortable, the discomfort is affected by not only the amplitude spectrum but also the phase spectrum. Here we examined how discomfort from flicker with differing temporal profiles also varies as a function of the mean light level and luminance contrast of the stimulus. Participants were asked to rate discomfort for a 17° flickering uniform field at different light levels from scotopic to photopic. The flicker waveform was varied with a square wave or random phase spectrum and filtered by modulating the slope of the amplitude spectrum relative to 1/f. At photopic levels, the 1/f square wave flicker appeared most comfortable, whereas the discomfort from the random flicker increased monotonically when the slope of the amplitude spectrum was shallow. This special status for the 1/f square wave condition was limited to photopic light levels. At the lower mesopic or scotopic levels, the effect of phase spectrum on the discomfort was diminished, with both phase spectra showing a monotonic change with the slope of the amplitude spectrum. We show that these changes cannot be accounted for by changes in the effective luminance contrast of the stimuli or
Visual discomfort refers to discomfort or pain in or around the eyes, often associated with heada... more Visual discomfort refers to discomfort or pain in or around the eyes, often associated with headache and/or nausea, and sometimes accompanied by signs such as red, itchy or watering eyes. The lighting conditions likely to cause visual discomfort are insufficient light for the task at hand, dramatic differences in illuminance around the task, shadows, veiling reflections, glare and flicker. To date, research on visual discomfort has been largely reactive, i.e. in response to complaints, but there is now proactive work that explores why discomfort occurs. The hypothesis underlying this work is that the human visual system has evolved to extract information from the natural world efficiently so that when the visual environment departs from the temporal, spatial or chromatic characteristics of the natural world, discomfort is likely because of inefficient neural processing. An important implication is that visual discomfort therefore depends on both the lighting and the dé cor of a space. Until this approach becomes more established, visual discomfort can be minimised by following carefully developed standards and guidance, by using products that meet appropriate standards, by paying attention to both lighting and dé cor and by being aware of the wide variation in individual sensitivity.
Kannada, one of the Dravidian languages, is the official language of Karnataka state of India. Th... more Kannada, one of the Dravidian languages, is the official language of Karnataka state of India. There is a need for a test using Kannada words that can assess visual aspects of reading independently of syntactic and semantic knowledge. A test of reading rate in Kannada was developed following the design principles of the Wilkins Rate of Reading Test (RRT). Fifteen high-frequency bisyllabic Kannada words were selected. Children were recruited from state and private schools that used Kannada or English as the medium of instruction. A total of 799 children from Grade 2 to 9 participated in the study. Reading rate was measured using the English RRT and the Kannada version twice in immediate succession during the first session. In 85 children, measurements using the Kannada RRT were repeated after an interval of 15 days. Pearson product moment correlation between the two immediately successive tests was 0.95 for the Kannada RRT and 0.91 for the English RRT. The correlation for the tests s...
222 SU-PM* BrainVISA: an extensible software environment for sharing multimodal neuroimaging data... more 222 SU-PM* BrainVISA: an extensible software environment for sharing multimodal neuroimaging data and (O-F2) processing tools,
Visual discomfort occurs when the statistics of the retinal image depart from those of natural sc... more Visual discomfort occurs when the statistics of the retinal image depart from those of natural scenes, particularly in respect of an excess energy at spatial frequencies close to 3 cycles/degree. Computer models suggest that uncomfortable stimuli are processed with a larger and less sparse neural response. Uncomfortable stimuli usually evoke a relatively large oxygenation of the visual cortex of the brain, consistent with inefficient neural encoding. The discomfort may be homeostatic. The neural computation that sustains sight is therefore likely to be more complex when the visual scene is spatially periodic, when the colour contrast is high or when saccadic suppression is impaired by flicker that is too rapid to be seen.
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Papers by Arnold Wilkins