Flicker and reading speed: Effects on individuals with visual sensitivity.

Flicker and patterns of stripes in the modern environment can evoke visual illusions, discomfort migraine, and seizures. We measured reading speed while striped and less striped texts were illuminated with LED lights. In Experiment 1, the lights flickered at 60 Hz and 120 Hz compared to 60 kHz (perceived as steady light). In Experiment 2, the lights flickered at 60 Hz or 600 Hz (at which frequency the phantom array is most visible), and were compared to continuous light. Two types of text were used: one containing words with high horizontal autocorrelation (striped) and another containing words with low autocorrelation (less striped). We measured the number of illusions participants saw in the Pattern Glare (PG) Test. Overall, reading speed was slowest during the 60 Hz and 600 Hz flicker and was slower when reading the high autocorrelation text. Interestingly, the low PG group showed greater effects of flicker on reading speed than the high PG group, which tended to be slower overall. In addition, reading speed in the high PG group was reduced when the autocorrelation of the text was high. These findings suggest that uncomfortable visual environments reduce reading efficiency, the more so in individuals who are visually sensitive.

Assessment of a Clinical Test for Detection of Alteration in Visual Perception Due to Astigmatism.

Purpose: Astigmatism blurs the retinal image of a circular spot along a particular orientation rendering it an elliptical shape. Astigmatic patients demonstrate adaptation to residual astigmatic blur that may affect their discrimination between oval and circular targets. The Wilkins Egg and Ball Test (WEBT) was created to detect altered visual perception due to residual astigmatic blur by discriminating a circle within a row of oval elements. This prospective, cross-sectional study examined the utility of WEBT in detecting uncorrected residual astigmatism on the perception of form symmetry in astigmatic and keratoconic participants as well as normal participants with induced astigmatism at four primary meridians. Methods: The mean search time (sT) and number of errors (noE) of 33 non-astigmatic controls (mean age: 24±5, range: 18-43, 6 males), 23 astigmatic participants (mean age: 36±12, range: 18-43, 6 males) and 13 keratoconic participants (N=22 eyes, mean age: 36±12, range: 18-58, 6 males) were measured under baseline, and 2.00 DC induced cylinder at four primary meridians, and for uncorrected, spherical-correction only, and fully corrected conditions, respectively. Mean sT and noE were converted to Z-scores, combined for each condition, and compared using repeated measures ANOVA with post-hoc analysis. Results: Combined Z-scores for the controls were significantly worse (p<0.001) for all induced cylinder conditions. The induced 180° condition was significantly better than 45° and 90° conditions (p=0.04), but not the 135° condition. For both astigmatic and keratoconic cohorts, Z-scores of the uncorrected condition were significantly worse than the fully corrected condition (both p<0.01), but the fully corrected and spherical-only conditions did not differ significantly (p=0.06 and p=0.05, respectively). Conclusion: In accommodating young adults, WEBT detected altered visual perception due to overall blur, and moderate-high amounts of uncorrected induced astigmatism and keratoconus, but is not useful as a tool for detection of altered visual perception due to small residual astigmatic blur.

Identification of the human cerebral cortical hemodynamic response to passive whole-body movements using near-infrared spectroscopy.

The human vestibular system is crucial for motion perception, balance control, and various higher cognitive functions. Exploring how the cerebral cortex responds to vestibular signals is not only valuable for a better understanding of how the vestibular system participates in cognitive and motor functions but also clinically significant in diagnosing central vestibular disorders. Near-infrared spectroscopy (NIRS) provides a portable and non-invasive brain imaging technology to monitor cortical hemodynamics under physical motion. Objective: This study aimed to investigate the cerebral cortical response to naturalistic vestibular stimulation induced by real physical motion and to validate the vestibular cerebral cortex previously identified using alternative vestibular stimulation. Approach: Functional NIRS data were collected from 12 right-handed subjects when they were sitting in a motion platform that generated three types of whole-body passive translational motion (circular, lateral, and fore-and-aft). Main results: The study found that different cortical regions were activated by the three types of motion. The cortical response was more widespread under circular motion in two dimensions compared to lateral and fore-and-aft motions in one dimensions. Overall, the identified regions were consistent with the cortical areas found to be activated in previous brain imaging studies. Significance: The results provide new evidence of brain selectivity to different types of motion and validate previous findings on the vestibular cerebral cortex.

Excessive fear of clusters of holes, its interaction with stressful life events and the association with anxiety and depressive symptoms: large epidemiological study of young people in Hong Kong.

BACKGROUND: Excessive and persistent fear of clusters of holes, also known as trypophobia, has been suggested to reflect cortical hyperexcitability and may be associated with mental health risks. No study, however, has yet examined these associations in representative epidemiological samples. AIMS: To examine the prevalence of trypophobia in a population-representative youth sample, its association with mental health and functioning, and its interaction with external stress. METHOD: A total of 2065 young people were consecutively recruited from a household-based epidemiological youth mental health study in Hong Kong. Trypophobia, symptoms of anxiety, depression and stress, and exposure to personal stressors were assessed. Logistic regression was used to assess the relationships between trypophobia and mental health. Potential additive and interaction effects of trypophobia and high stress exposure on mental health were also tested. RESULTS: The prevalence of trypophobia was 17.6%. Trypophobia was significantly associated with severe symptoms of anxiety (odds ratio (OR) = 1.83, 95% CI = 1.32-2.53), depression (OR = 1.78, 95% CI = 1.24-2.56) and stress (OR = 1.68, 95% CI = 1.11-2.53), even when accounting for sociodemographic factors, personal and family psychiatric history, resilience and stress exposure. Dose-response relationships were observed, and trypophobia significantly potentiated the effects of stress exposure on symptom outcomes, particularly for depressive symptoms. Those with trypophobia also showed significantly poorer functioning across domains and poorer health-related quality of life. CONCLUSIONS: Screening for trypophobia in young people may facilitate early risk detection and intervention, particularly among those with recent stress exposure. Nevertheless, the generally small effect sizes suggest that other factors have more prominent roles in determining recent mental health outcomes in population-based samples; these should be explored in future work.

A mechanistic account of visual discomfort.

Much of the neural machinery of the early visual cortex, from the extraction of local orientations to contextual modulations through lateral interactions, is thought to have developed to provide a sparse encoding of contour in natural scenes, allowing the brain to process efficiently most of the visual scenes we are exposed to. Certain visual stimuli, however, cause visual stress, a set of adverse effects ranging from simple discomfort to migraine attacks, and epileptic seizures in the extreme, all phenomena linked with an excessive metabolic demand. The theory of efficient coding suggests a link between excessive metabolic demand and images that deviate from natural statistics. Yet, the mechanisms linking energy demand and image spatial content in discomfort remain elusive. Here, we used theories of visual coding that link image spatial structure and brain activation to characterize the response to images observers reported as uncomfortable in a biologically based neurodynamic model of the early visual cortex that included excitatory and inhibitory layers to implement contextual influences. We found three clear markers of aversive images: a larger overall activation in the model, a less sparse response, and a more unbalanced distribution of activity across spatial orientations. When the ratio of excitation over inhibition was increased in the model, a phenomenon hypothesised to underlie interindividual differences in susceptibility to visual discomfort, the three markers of discomfort progressively shifted toward values typical of the response to uncomfortable stimuli. Overall, these findings propose a unifying mechanistic explanation for why there are differences between images and between observers, suggesting how visual input and idiosyncratic hyperexcitability give rise to abnormal brain responses that result in visual stress.

Visual-stress-related cortical excitability as a prospective marker for symptoms of depression and anxiety in young people.

Visual stress is thought to reflect cortical excitability and has been associated with many neurological, neuropsychiatric, and neurodevelopmental conditions. However, its relationships with symptoms of depression and anxiety have not yet been elucidated. We conducted two separate studies to first examine visual stress in a longitudinal community sample of 104 participants (aged 12-24) in association with prospective symptoms of depression, anxiety, and distress after 3 months, and subsequently in a cross-sectional epidemiological sample of 530 participants (aged 15-24) to validate its associations with current mood and distress symptoms. The Pattern Glare Test was used to examine visual stress to three grating patterns with the spatial frequencies (SF) of 0.3, 2.3, and 9.4 cycles per degree (cpd). Other known factors of mental health, including functioning, as well as resilience, hopelessness, and loneliness, were also assessed at baseline. In both studies, we showed that perceptual distortions were highest toward the pattern with mid-SF (2.3 cpd). Multiple linear regression analyses revealed that greater visual stress was significantly associated with not only baseline but also 3-month symptom outcomes, even when accounting for age, years of education, days of no functioning, resilience, hopelessness, and loneliness. Our findings suggest the importance of visual stress in understanding and predicting poor mental health outcomes. As mental health can lead to far-reaching consequences that extend to adulthood, our findings may inform state-of-the-art innovative strategies for the prediction of poor mental health outcomes and suggest visual stress as a potential marker for early risk detection among young people.

Visually sensitive seizures: An updated review by the Epilepsy Foundation.

Light flashes, patterns, or color changes can provoke seizures in up to 1 in 4000 persons. Prevalence may be higher because of selection bias. The Epilepsy Foundation reviewed light-induced seizures in 2005. Since then, images on social media, virtual reality, three-dimensional (3D) movies, and the Internet have proliferated. Hundreds of studies have explored the mechanisms and presentations of photosensitive seizures, justifying an updated review. This literature summary derives from a nonsystematic literature review via PubMed using the terms "photosensitive" and "epilepsy." The photoparoxysmal response (PPR) is an electroencephalography (EEG) phenomenon, and photosensitive seizures (PS) are seizures provoked by visual stimulation. Photosensitivity is more common in the young and in specific forms of generalized epilepsy. PS can coexist with spontaneous seizures. PS are hereditable and linked to recently identified genes. Brain imaging usually is normal, but special studies imaging white matter tracts demonstrate abnormal connectivity. Occipital cortex and connected regions are hyperexcitable in subjects with light-provoked seizures. Mechanisms remain unclear. Video games, social media clips, occasional movies, and natural stimuli can provoke PS. Virtual reality and 3D images so far appear benign unless they contain specific provocative content, for example, flashes. Images with flashes brighter than 20 candelas/m2 at 3-60 (particularly 15-20) Hz occupying at least 10 to 25% of the visual field are a risk, as are red color flashes or oscillating stripes. Equipment to assay for these characteristics is probably underutilized. Prevention of seizures includes avoiding provocative stimuli, covering one eye, wearing dark glasses, sitting at least two meters from screens, reducing contrast, and taking certain antiseizure drugs. Measurement of PPR suppression in a photosensitivity model can screen putative antiseizure drugs. Some countries regulate media to reduce risk. Visually-induced seizures remain significant public health hazards so they warrant ongoing scientific and regulatory efforts and public education.

The Functional Network of the Visual Cortex Is Altered in Migraine.

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 evidence that the functional network was altered in migraine between headaches. The functional network was bilateral in the control participants but substantially lateralized in the migraine patients. The results also indicated different effects of colored lenses on the functional network for both participant groups.

Precision, reliability and application of the Wilkins Rate of Reading Test.

BACKGROUND: The Wilkins Rate of Reading Test (WRRT) enables rapid measurement of reading speed using text passages that have no semantic content and demand minimal word recognition skills. It is suited to applications where the primary interest is in the influence of visual and ocular motor factors on reading rate. METHODS: We obtained estimates of precision and reliability of WRRT from four data samples (A-D) collected independently by the authors: (A) n = 118 adults; (B) n = 90 adults; (C) n = 787 children; (D) n = 134 children. Each participant was asked to read aloud as quickly and accurately as possible, for 1 min, and results were recorded as number of words read correctly per minute (wcpm). RESULTS: Estimates of precision are given by the within-subjects standard deviation sw , and reliability by the intraclass correlation coefficient for single measurements r1 . For each sample these estimates were (A) sw  = 11.5 wcpm, r1  = 0.85; (B) sw  = 3.8 wcpm, r1  = 0.98; (C) sw  = 6.7 wcpm, r1  = 0.93; (D) sw  = 6.2 wcpm, r1  = 0.94. CONCLUSION: The reliability of WRRT reflects large variation in reading rate between individuals compared to within-individual variability, indicating that it is a good test for discriminating differences in reading speed between individuals. The precision of the test varies from 3.8 wcpm to 11.5 wcpm among samples, and the pooled value of 7.2 wcpm, provides a basis for setting a population-wide criterion for minimum detectable change of reading rate in individuals over time. Nevertheless, a preferable way of monitoring change in an individual would be to use a criterion determined from estimates of that individual's baseline variation in WRRT scores.

Pattern-sensitive patients with epilepsy use uncomfortable visual stimuli to self-induce seizures.

Sensory stimuli can induce seizures in patients with epilepsy and predisposed subjects. Visual stimuli are the most common triggers, provoking seizures through an abnormal response to light or pattern. Sensitive patients may intentionally provoke their seizures through visual stimuli. Self-induction methods are widely described in photo-sensitive patients, while there are only a few reports of those who are pattern-sensitive. We analyzed 73 images of environmental visual triggers collected from 14 pattern-sensitive patients with self-induced seizures. The images were categorized according to their topics: 29 Objects (43%); 19 Patterns (28%); 15 External scenes (22%); 4 TV or computer screens (6%). Six photos were of poor quality and were excluded from analysis. Images were analyzed by an algorithm that calculated the degree to which the Fourier amplitude spectrum differed from that in images from nature. The algorithm has been shown to predict discomfort in healthy observers. The algorithm identified thirty-one images (46%) as "uncomfortable". There were significant differences between groups of images (ANOVA p = .0036; Chi2 p < .0279), with higher values of difference from nature in the images classified as "Objects" (mean 6,81E+11; SD 6,72E+11; n.17, 59%) and "Pattern" (mean 9,05E+11; SD 6,86E+11; n.14, 74%). During the semi-structured face-to-face interviews, all patients described the visual triggers as 'uncomfortable'; the appearance of enjoyable visual epileptic symptoms (especially multi-colored hallucinations) transformed uncomfortable images into pleasant stimuli. Patients considered self-induction as the simplest and most effective way to overcome stressful situations, suggesting that self-inducing pattern-sensitive patients often use uncomfortable visual stimuli to trigger their seizures. Among the reasons for the self-inducing behavior, the accidental discovery of pleasurable epileptic symptoms related to these "uncomfortable" visual stimuli should be considered.

Photophobia in migraine: A symptom cluster?

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 conditions may offer better specificity in identifying biomarkers and possible mechanisms to target for treatment.

Visual Discomfort and Variations in Chromaticity in Art and Nature.

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 discloses a new link between visual ecology and discomfort whereby discomfort arises when adaptive perceptual mechanisms are overstimulated by specific classes of stimuli rarely found in nature.

Trypophobia: Heart rate, heart rate variability and cortical haemodynamic response.

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 both 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.

Visual discomfort from flicker: Effects of mean light level and contrast.

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 as the slope of the amplitude spectrum decreased. 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 by the responses from a linear model based on the temporal impulse responses under different light levels. However, discomfort from flicker is robustly correlated with judgments of the perceived naturalness of flicker across different contrasts and mean luminance levels.

Preference for Lighting Chromaticity in Migraine With Aura.

OBJECTIVE: We studied the color of lighting chosen as comfortable for reading by individuals with migraine and controls. We explored the effects of the chosen color on visual performance. BACKGROUND: It has been reported that individuals who experience migraine with aura (MWA) choose, as comfortable for reading, light that is more strongly saturated in color than that chosen by individuals without migraine. METHODS: A convenience sample of 18 individuals who experienced MWA, 18 without aura, and 18 controls without migraine participated in a cross-sectional laboratory study at Anglia Ruskin University. We used an Intuitive Colorimeter that illuminated text with colored light and permitted the separate control of hue (color) and saturation (strength of color) without a change in luminance. We selected individuals with migraine and healthy controls from the general population. They were headache-free in the 48 hours prior to testing. We used a routine that permitted the selection of the most comfortable hue from 12 alternatives and then alternately optimized the saturation and hue using small changes, thereby allowing for color adaptation. Visual performance at a word search task was measured under white light and under light of a color chosen as comfortable, using colored lenses. RESULTS: Healthy individuals chose light with chromaticity close to the Planckian locus, which approximates the chromaticities of daylight and most electric lighting. The distance from the locus averaged 0.029 (SD 0.021). Individuals who experienced MWA chose strongly saturated colors well away from the Planckian locus (average distance 0.056, SD 0.022). Individuals who experienced migraine without aura chose intermediate chromaticities (average distance 0.034, SD 0.022). Overall there was a large statistically significant difference between participant groups that explained 24% variance. Visual search time of individuals with migraine aura decreased from 22.5 to 16.8 s when light of the chosen color was provided using tinted lenses (the average increase in search speed was 45.7%). The lenses had no statistically significant effect on the performance of individuals without migraine aura. CONCLUSIONS: Individuals who experienced MWA selected as comfortable colors that deviated from the lighting typically experienced in everyday life. Possibly, individuals who experience MWA may be more susceptible to photophobia under typical lighting. Visual performance was improved using lenses that provided light of the chosen comfortable color. The spectral power of that choice showed no evident relationship to melanopic energy (energy captured by the intrinsically photosensitive retinal ganglion cells).

The Influence of Typography on Algorithms that Predict the Speed and Comfort of Reading.

1. The speed with which text can be read is determined in part by the spatial regularity and similarity of vertical letter strokes as assessed by the height of the first peak in the horizontal autocorrelation of the text. The height of this peak was determined for two passages in 20 fonts. The peak was unaffected by the size of the text or its content but was influenced by the font design. Sans serif fonts usually had a lower peak than serif fonts because the presence of serifs usually (but not invariably) resulted in a more even spacing of letter strokes. There were small effects of justification and font-dependent effects of font expansion and compression. 2. The visual comfort of images can be estimated from the extent to which the Fourier amplitude spectrum conforms to 1/f. Students were asked to adjust iBooks to obtain their preferred settings of font and layout. The preference was predicted by the extent to which the Fourier amplitude spectrum approximated 1/f, which in turn was jointly affected by the design of the font, its weight and the ratio of x-height to line separation. Two algorithms based on the autocorrelation and Fourier transformation of text can be usefully applied to any orthography to estimate likely speed and comfort of reading.

Vision and Hyper-Responsiveness in Migraine.

: We investigated contrast processing in relation to visual comfort from coloured light in individuals with migraine. In Experiment 1, 24 individuals who experienced migraine with aura (MA), 15 migraine without aura (MO), and 23 healthy controls, identified which of four patterns, one in each quadrant, had the greatest contrast. Although there were no significant differences between groups, contrast discrimination was superior in the visual field affected by aura in all eight participants in whom the aura was consistently lateralised. In Experiment 2, 20 participants without aura and 20 controls selected comfortable light with a chromaticity close to the daylight (Planckian) locus, whilst 20 individuals with aura chose more strongly saturated colours, mostly distant from the locus. In Experiment 3, nine participants with consistently unilateral aura undertook the contrast discrimination task wearing (a) lenses that provided a comfortable colour of light and (b) grey lenses of similar transmission. With grey lenses, seven of the nine individuals with unilateral aura showed a superior performance in the affected field, as before. With lenses providing a comfortable colour, however, the performance was relatively poor for the nine individuals with unilateral aura, but not for the 10 controls. This was the case in both visual fields. The cortical hyper-responsiveness with which migraine is associated may improve the perception of contrast. The perception is poorer (and more normal) with ophthalmic lenses having a comfortable colour.

Clinical Use of the Kannada and English Rate of Reading Tests.

The rate of reading test in which randomly ordered common words are read aloud has found use in optometric and educational practice as a means of assessing visual aspects of reading largely independently of comprehension. English and Kannada versions of the rate of reading test were administered to 761 children aged between 9 and 15 years. These children were recruited from four private and five state schools in Udupi Taluk that had English and Kannada, respectively, as the principal medium of instruction. The results showed that the reading rate increased with age, as expected, but depended on the language of the test and the medium of instruction. The study emphasizes the importance of using normative data based on age and the language of instruction used in school. It also suggests age-specific criteria to measure the efficacy of any visual intervention aimed at improving reading speed. The test can be used to assess (1) educational under-performance in reading and (2) the effects of optometric and educational intervention, and separate norms appropriate for each use are presented.