Visual discomfort: the influence of spatial frequency

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.

Visual Sensitivity in Complex Regional Pain Syndrome and Fibromyalgia: An Online Study

Perceptual anomalies can provide insights into underlying pathologies even when they are not the main symptom of many clinical conditions. Complex regional pain syndrome (CRPS) and fibromyalgia are chronic pain conditions associated with changes in the central nervous system, possibly leading to enhanced visual sensitivity. It is unclear whether this occurs more than for people with other types of pain. We examined visual sensitivity elicited by different stimuli and in daily life, through an online study of people with CRPS (n = 57), fibromyalgia (n = 74), other pain (n = 50), and no pain (n = 89). Respondents rated changes in pain, discomfort, or distress from viewing patterns with different spatial frequencies (lower-order visual processing), and reversible figures (bistable images; higher-order visual processing). We assessed visual sensitivity in daily life using the Leiden Visual Sensitivity Scale and Visual Discomfort Scale. Respondents with CRPS or fibromyalgia reported more visual discomfort than pain-related and pain-free controls while viewing striped patterns and a circle, with no effect of spatial frequency. They reported more pain while viewing a nonreversible square, but not reversible figures (Necker Cube, Duck/Rabbit). Finally, they reported more daily visual sensitivity than pain-related and pain-free controls. Suppressing visual cortical activity might benefit people with CRPS or fibromyalgia.

What is the Link Between Mental Imagery and Sensory Sensitivity? Insights from Aphantasia

People with aphantasia have impoverished visual imagery so struggle to form mental pictures in the mind's eye. By testing people with and without aphantasia, we investigate the relationship between sensory imagery and sensory sensitivity (i.e., hyper- or hypo-reactivity to incoming signals through the sense organs). In Experiment 1 we first show that people with aphantasia report impaired imagery across multiple domains (e.g., olfactory, gustatory etc.) rather than simply vision. Importantly, we also show that imagery is related to sensory sensitivity: aphantasics reported not only lower imagery, but also lower sensory sensitivity. In Experiment 2, we showed a similar relationship between imagery and sensitivity in the general population. Finally, in Experiment 3 we found behavioural corroboration in a Pattern Glare Task, in which aphantasics experienced less visual discomfort and fewer visual distortions typically associated with sensory sensitivity. Our results suggest for the very first time that sensory imagery and sensory sensitivity are related, and that aphantasics are characterised by both lower imagery, and lower sensitivity. Our results also suggest that aphantasia (absence of visual imagery) may be more accurately defined as a subtype of a broader imagery deficit we name dysikonesia, in which weak or absent imagery occurs across multiple senses.

The effects of visual discomfort and chromaticity separation on neural processing during a visual task

Visual stimuli that are uncomfortable to look at evoke a large neural response suggesting altered processing. While there is some evidence linking uncomfortable achromatic stimuli to impaired visual processing, the effect of uncomfortable chromatic patterns on visual cognition has yet to be explored. Large differences in chromaticity separation (e.g. red and blue) elicit visual discomfort, larger metabolic responses, larger visual evoked potentials, and greater alpha suppression compared to small chromaticity separations (e.g. pink and purple). We investigated the impact of stimuli that varied in their chromaticity separation (calculated in perceptual color space) on a visual task and their effect on neural responses across the cortex. Thirty participants completed a continuous pairs task (letters changed at 3 Hz) while grating patterns that differed in their chromaticity separation alternated with a grey screen at 5 Hz. The different temporal frequencies allowed for steady-state visual evoked potentials (SSVEPs) to the two stimulus-types to be measured simultaneously using electroencephalography (EEG). A subset of participants rated the gratings on a 9-point scale of discomfort. We observed greater ratings of discomfort and increased power at 5 Hz with the larger chromaticity separations. The increase in 5 Hz power with greater chromaticity separation was evident across the cortex. However, there was no significant effect of chromaticity separation on power at 3 Hz, or on reaction times, and no consistent effect on behavioral accuracy. Despite eliciting heightened neural responses across the cortex, short term exposure to uncomfortable chromatic stimuli does not adversely impact visual task performance.

Validation of the Leiden Visual Sensitivity Scale and Visual Discomfort Scale in Chronic Pain Conditions

Discomfort provoked by normally innocuous visual stimuli has been reported by people with chronic pain. Visual discomfort may be higher in pain conditions in which central sensitization is implicated, such as Complex Regional Pain Syndrome (CRPS) and fibromyalgia. In an online study, we validated the Leiden Visual Sensitivity Scale (L-VISS) and Visual Discomfort Scale (VDS) in people with CRPS (n = 57), fibromyalgia (n = 75), and general chronic pain (n = 53); investigated whether these groups and pain-free controls (n = 125) differed in visual discomfort; and evaluated the effect of age. The L-VISS and VDS had good internal consistency. Both scales were positively related with experimentally induced visual distortions for mid-spatial frequency striped patterns, suggesting good construct validity. The scales were positively related with each other, and dissociated between the pain and pain-free groups in similar ways, suggesting good construct validity. There was no relationship between age and L-VISS scores and a small negative relationship between age and VDS scores. Visual discomfort was highest in the fibromyalgia group, followed by the CRPS group. This research confirms the utility of the L-VISS and VDS for measuring visual sensitivity in chronic pain and adds to evidence that central sensitization is an important mechanism of visual discomfort.

Differential Effects of Orientation and Spatial-Frequency Spectra on Visual Unpleasantness

Increasing psychophysical evidence suggests that specific image features – or statistics – can appear unpleasant or induce visual discomfort in humans. Such unpleasantness tends to be particularly profound if the image’s amplitude spectrum deviates from the regular 1/f spatial-frequency falloff expected in natural scenes. Here, we show that profound unpleasant impressions also result if the orientation spectrum of the image becomes flatter. Using bandpass noise with variable orientation and spatial-frequency bandwidths, we found that unpleasantness ratings decreased with spatial- frequency bandwidth but increased with orientation bandwidth. Similarly, a subsequent experiment revealed that sinusoidal modulations in the amplitude spectrum of 1/f noise along the spatial frequency increased unpleasantness, but modulations along the orientation decreased it. Given that natural scenes tend to have a linear slope along the spatial frequency but an uneven spectrum along the orientation dimension, our opposing results in the spatial-frequency and orientation domains commonly support the idea that images deviating from the spectral regularity of natural scenes can give rise to unpleasant impressions.

Visual Perception of Moisture Is a Pathogen Detection Mechanism of the Behavioral Immune System

The behavioral immune system (BIS) includes perceptual mechanisms for detecting cues of contamination. Former studies have indicated that moisture has a disgusting property. Therefore, moisture could be a target for detecting contamination cues by the BIS. We conducted two experiments to examine the psychophysical basis of moisture perception and clarify the relationship between the perception of moisture and the BIS. We assumed that the number of high luminance areas in a visual image provided optical information that would enable the visual perception of moisture. In two experiments, we presented eight images of dough that contained different amounts of moisture as experimental stimuli. The amount of moisture shown in the images was increased in eight steps, from 28.6 to 42.9% of the total weight of the dough. In Experiment 1, the images were randomly presented on a computer display, and the participants (n = 22) were asked to rank the images in the order of the visually perceived moisture content. In Experiment 2, the participants (n = 15) completed pairwise comparisons based on the perceived moistness of the images. Furthermore, to examine the BIS responses, the participants rated the strength of disgust evoked by the stimuli, their motivation to avoid touching the stimuli, and the estimated magnitude of the risk of contamination by physical contact with the stimuli. The results indicated that the moisture content and the numbers of high luminance areas in the images accurately predicted the perception of moisture, suggesting that the detection of visual moisture was highly accurate, and the optical information served as an essential perceptual cue for detecting moisture. On the other hand, the BIS responses peaked in response to stimuli having approximately 33 to 39% moisture content. These results show that objects containing a moderate amount of moisture could be the target of visually detecting pathogens by the BIS.

Development of the Japanese version of the Visual Discomfort Scale

BACKGROUND

Visual stimuli, such as stripes and texts, can induce "visual discomfort" including perceptual and somatic symptoms. Individuals reporting high levels of visual discomfort might experience migraine headache and may have reduced reading efficiency due to visual perceptual difficulties. This study aimed to develop and validate the Japanese version of the Visual Discomfort Scale, which measures proneness to visual discomfort.

METHODS AND RESULTS

In Survey 1, 428 adults completed the Japanese version and a questionnaire assessing migraine morbidity. Rasch analysis revealed that the Japanese version is a unidimensional scale with a high amount of unexplained variance due to random noise rather than another dimension, and has high person and item reliabilities. Participants with migraine exhibited high scores in the Japanese version, indicating the construct validity of the scale. Survey 2 with 118 adults revealed a strong test-retest correlation for the Japanese version, indicating the stability of the scale.

CONCLUSION

The Japanese version of the Visual Discomfort Scale is a sufficiently reliable and valid scale for assessing visual discomfort, although its unidimensionality leaves room for further improvements.

Atypical sensory sensitivity as a shared feature between synaesthesia and autism

Several studies have suggested that there is a link between synaesthesia and autism but the nature of that link remains poorly characterised. The present study considers whether atypical sensory sensitivity may be a common link between the conditions. Sensory hypersensitivity (aversion to certain sounds, touch, etc., or increased ability to make sensory discriminations) and/or hyposensitivity (desire to stimulate the senses , or a reduced response to sensory stimuli are a recently introduced diagnostic feature of autism spectrum conditions (ASC). Synaesthesia is defined by unusual sensory experiences and has also been linked to a typical cortical hyper-excitability. The Glasgow Sensory Questionnaire (GSQ) was administered to synaesthetes and people with ASC. Both groups reported increased sensory sensitivity relative to controls with a large effect size. Both groups also reported a similar pattern of both increased hyper- and hypo-sensitivities across multiple senses. The AQ (Autism-Spectrum Quotient) scores were elevated in the synaesthetes, and one subscale of this measure (attention to detail) placed synaesthetes within the autistic range. A standard laboratory test of visual stress (the Pattern Glare Test), administered online, corroborated the findings of increased sensitivity to aversive visual stimuli in synaesthetes. We conclude that atypical sensory sensitivity is an important shared feature between autism and synaesthesia.

A systematic review of controlled trials on visual stress using Intuitive Overlays or the Intuitive Colorimeter

Claims that coloured filters aid reading date back 200 years and remain controversial. Some claims, for example, that more than 10% of the general population and 50% of people with dyslexia would benefit from coloured filters lack sound evidence and face validity. Publications with such claims typically cite research using methods that have not been described in the scientific literature and lack a sound aetiological framework. Notwithstanding these criticisms, some researchers have used more rigorous selection criteria and methods of prescribing coloured filters that were developed at a UK Medical Research Council unit and which have been fully described in the scientific literature. We review this research and disconfirm many of the more extreme claims surrounding this topic. This literature indicates that a minority subset of dyslexics (circa 20%) may have a condition described as visual stress which most likely results from a hyperexcitability of the visual cortex. Visual stress is characterised by symptoms of visual perceptual distortions, headaches, and eyestrain when viewing repetitive patterns, including lines of text. This review indicates that visual stress is distinct from, although sometimes co-occurs with, dyslexia. Individually prescribed coloured filters have been shown to improve reading performance in people with visual stress, but are unlikely to influence the phonological and memory deficits associated with dyslexia and therefore are not a treatment for dyslexia. This review concludes that larger and rigorous randomised controlled trials of interventions for visual stress are required. Improvements in the diagnosis of the condition are also a priority.

Lexical decisions in adults with low and high susceptibility to pattern-related visual stress: a preliminary investigation

Pattern-related visual stress (PRVS) is a form of sensory hypersensitivity that some people experience when viewing high contrast repeating patterns, notably alternating dark and light stripes. Those susceptible to PRVS typically have a strong aversion to such stimuli, and this is often accompanied by experiences of visual discomfort and disturbance. The patterns most likely to elicit symptoms of PRVS have a square-wave grating configuration of spatial frequency ~3 cycles/degree. Such stimuli are characteristic of printed text in which lines of words and the spaces between them present a high contrast grating-like stimulus. Consequently, much printed reading material has the potential to elicit PRVS that may impair reading performance, and this problem appears to be common in individuals with reading difficulties including dyslexia. However, the manner in which PRVS affects reading ability is unknown. One possibility is that the early sensory visual stress may interfere with the later cognitive word recognition stage of the reading process, resulting in reading performance that is slower and/or less accurate. To explore the association of PRVS with word recognition ability, lexical decision performance (speed and accuracy) to words and pronounceable non-words was measured in two groups of adults, having low and high susceptibility to PRVS. Results showed that lexical decisions were generally faster but less accurate in high-PRVS, and also that high-PRVS participants made decisions significantly faster for words than for non-words, revealing a strong lexicality effect that was not present in low-PRVS. These findings are novel and, as yet, unconfirmed by other studies.

Signs of increased cortical hyperexcitability selectively associated with spontaneous anomalous bodily experiences in a nonclinical population

INTRODUCTION

The current study examined the presence of cortical hyperexcitability, in nonclinical hallucinators, reporting different forms of anomalous bodily experiences (ABEs). Groups reporting visual out-of-body experiences and nonvisual sensed-presence experiences were examined. It was hypothesised that only those hallucinators whose experiences contained visual elements would show increased signs of visual cortical hyperexcitability.

METHODS

One hundred and eighty-two participants completed the "Pattern-glare task" (involving the viewing of striped gratings with spatial frequencies irritable to visual cortex)-a task known to reflect degrees of cortical hyperexcitability associated with hallucinatory/aura experiences in neurological samples. Participants also completed questionnaire measures of anomalous "temporal-lobe experience" and predisposition to anomalous visual experiences.

RESULTS

Those reporting increased levels of anomalous bodily experiences provided significantly elevated scores on measures of temporal-lobe experience. Only the visual OBE group reported significantly elevated levels of cortical hyperexcitability as assessed by the pattern-glare task.

CONCLUSIONS

Collectively, the results are consistent with there being an increased degree of background cortical hyperexcitability in the cortices of individuals predisposed to some ABE-type hallucinations, even in the nonclinical population. The present study also establishes the clinical utility of the pattern-glare task for examining signs of aberrant visual connectivity in relation to visual hallucinations.

Visual search and visual discomfort

Certain visual stimuli evoke perceptions of discomfort in non-clinical populations. We investigated the impact of stimuli previously judged as uncomfortable by non-clinical populations on a visual search task. One stimulus that has been shown to affect discomfort judgments is noise that has been filtered to have particular statistical properties (Juricevic et al, 2010 Perception 39 884-899). A second type of stimulus associated with visual discomfort is striped patterns (Wilkins et al, 1984 Brain 107 989-1017). These stimuli were used as backgrounds in a visual search task, to determine their influence on search performance. Results showed that, while striped backgrounds did have an impact on visual search performance, this depended on the similarity between the target and background in orientation and spatial frequency. We found no evidence for a more generalised effect of discomfort on performance.

Susceptibility to pattern glare following stroke

The aim of this work was to measure susceptibility to pattern glare within a stroke group, employing a direct method of assessment. Twenty stroke subjects, aged 38–85 years, were recruited, along with an age-matched control group (n = 20). Assessment of pattern glare susceptibility was undertaken using the pattern glare test. An abnormal degree of pattern glare is present when individuals score[1 on the mid-high spatial frequency difference variable, a relative score that allows for normalization of the subject, or [3 when viewing the mid spatial frequency grating. Stroke subjects demonstrate elevated levels of pattern glare compared to normative data values and a control population, as determined using the pattern glare test. This was most notable when considering the output measure for the mid-high difference variable. The mean score for the mid-high difference variable was 2.15 SD 1.27 for the stroke subjects versus 0.10 SD 1.12 for the control subjects. When considering the mid-high difference variable, 75% of the stroke group recorded an abnormal level of pattern glare compared to 5% in the control group. This study demonstrates an association between stroke subjects and elevated levels of pattern glare. Cortical hyperexcitability has been shown to present following stroke, and this has been proposed as a plausible explanation for the perceptual distortions experienced by individuals susceptible to pattern glare. Further work to assess the benefits of spectral filters in reducing perceptual distortions in stroke patients is currently underway.

Detection and discrimination of flicker contrast in migraine

AIMS

Flickering light is strongly aversive to many individuals with migraine. This study was designed to evaluate other abnormalities in the processing of temporally modulating visual stimulation.

METHODS

We measured psychophysical thresholds for detection of a flickering target and for the discrimination of suprathreshold flicker contrasts (increment thresholds) in 14 migraineurs and 14 healthy controls with and without prior adaptation to high-contrast flicker. Visual discomfort (aversion) thresholds were also assessed.

RESULTS

In the baseline (no adaptation) conditions, detection and discrimination thresholds did not differ significantly between groups. Following adaptation, flicker detection thresholds were elevated equivalently in both groups; however, discrimination thresholds were more strongly affected in migraineurs than in controls, showing greater elevation at moderate contrasts and greater threshold reduction (sensitisation) at high contrast (70%). Migraineurs also had significantly elevated discomfort scores, and these were significantly correlated with number of years with migraine.

DISCUSSION

We conclude that visual flicker not only causes discomfort but also exerts measurable effects on contrast processing in the visual pathways in migraine. The findings are discussed in the context of the existing literature on habituation, adaptation and contrast-gain control.

The Pattern Glare Test: a review and determination of normative values

Pattern glare is characterised by symptoms of visual perceptual distortions and visual stress on viewing striped patterns. People with migraine or Meares-Irlen syndrome (visual stress) are especially prone to pattern glare. The literature on pattern glare is reviewed, and the goal of this study was to develop clinical norms for the Wilkins and Evans Pattern Glare Test. This comprises three test plates of square wave patterns of spatial frequency 0.5, 3 and 12 cycles per degree (cpd). Patients are shown the 0.5 cpd grating and the number of distortions that are reported in response to a list of questions is recorded. This is repeated for the other patterns. People who are prone to pattern glare experience visual perceptual distortions on viewing the 3 cpd grating, and pattern glare can be quantified as either the sum of distortions reported with the 3 cpd pattern or as the difference between the number of distortions with the 3 and 12 cpd gratings, the '3-12 cpd difference'. In study 1, 100 patients consulting an optometrist performed the Pattern Glare Test and the 95th percentile of responses was calculated as the limit of the normal range. The normal range for the number of distortions was found to be <4 on the 3 cpd grating and <2 for the 3-12 cpd difference. Pattern glare was similar in both genders but decreased with age. In study 2, 30 additional participants were given the test in the reverse of the usual testing order and were compared with a sub-group from study 1, matched for age and gender. Participants experienced more distortions with the 12 cpd grating if it was presented after the 3 cpd grating. However, the order did not influence the two key measures of pattern glare. In study 3, 30 further participants who reported a medical diagnosis of migraine were compared with a sub-group of the participants in study 1 who did not report migraine or frequent headaches, matched for age and gender. The migraine group reported more symptoms on viewing all gratings, particularly the 3 cpd grating. The only variable to be significantly different between the groups was the 3-12 cpd difference. In conclusion, people have an abnormal degree of pattern glare if they have a Pattern Glare Test score of >3 on the 3 cpd grating or a score of >1 on the 3-12 cpd difference. The literature suggests that these people are likely to have visual stress in everyday life and may therefore benefit from interventions designed to alleviate visual stress, such as precision tinted lenses.

Visual processing characteristics of children with Meares-Irlen syndrome

The potential role of visual processing deficits in reading difficulty was brought to public attention by claims that a large proportion of children with dyslexia suffer from a perceptual dysfunction currently referred to as Meares-Irlen syndrome (MISViS). A previous study showing that visual perceptual measures involving visual memory and discrimination predict independent variance in reading achievement [J. Learn. Disabil. 28 (1995) 216] provides a basis to examine their relationships with the diagnostic criteria of MISViS. This study examined these visual processing characteristics in 36 eight- to ten-year-old children, half of whom were experiencing reading difficulty. Children were assessed for MISViS by Irlen screeners; approximately half of the participants in each group were positively identified. Concurrent performance on standardized visual processing tests showed that while a positive diagnosis of MISViS is not indicative of reading ability, nor in particular of a visual-processing deficit subtype identified by Watson and Willows [J. Learn. Disabil. 28 (1995) 216], MISViS can indicate visual processing difficulties potentially related to visual attention inefficiency.

Effects of Luminance Ratio in a Liquid-Crystal Display on Discrimination of Separation by Elderly People

In a 2006 study the influence of spacing between vertical lines, exposure time, and number of vertical lines on visual performance was identified. The present study further explored the effects of luminance ratio on discrimination of separation. Analysis showed the luminance ratio of target vertical lines affected the visual performance of both younger and elderly people. The luminance ratio was greater, as was accuracy; however, accuracy might not become greater when the luminance ratio was too high. Further, the effect of the number of vertical lines on accuracy was significant, as was consistent with the 2006 study. Two interactive two-way effects were found, group × luminance ratio and luminance ratio × number of vertical lines.

Use of the Hermann grid illusion in the measurement of contrast perception in dyslexia

We measured contrast thresholds for perception of the Hermann grid illusion, using different contrast polarities and mean luminances, in dyslexics and non-dyslexics. Both groups of subjects gave significantly lower thresholds with grids having dark squares and light paths, but there was no significant threshold difference between groups. Perceived strength of illusion was also measured in grids at suprathreshold contrast levels. Dyslexics perceived the illusion to be significantly stronger than non-dyslexics when the grid had light paths and low luminance.

The optometric correlates of migraine

Migraine is a common, chronic, multi-factorial, neuro-vascular disorder typically characterised by recurrent attacks of unilateral, pulsating headache and autonomic nervous system dysfunction. Migraine may additionally be associated with aura; those focal neurological symptoms that may precede or sometimes accompany the headache. This review describes the optometric aspects of migraine headache. There have been claims of a relationship between migraine headaches and errors of refraction, binocular vision anomalies, pupil anomalies, visual field changes and pattern glare. The quality of the evidence for a relationship between errors of refraction and binocular vision and migraine is poor. The quality of the evidence to suggest a relationship between migraine headache and pupil anomalies, visual field defects and pattern glare is stronger. In particular the link between migraine headache and pattern glare is striking. The therapeutic use of precision-tinted spectacles to reduce pattern glare (visual stress) and to help some migraine sufferers is described.

Visual search in migraine and visual discomfort groups

Two experiments that investigate automatic and conscious attention among migraine and visual discomfort groups are reported. The prediction of a heightened sensory sensitivity producing a processing speed advantage in migraine was tested. In Experiment 1, an automatic attention task was conducted. There was no effect of migraine group, but the high visual discomfort group responded significantly more slowly than the low visual discomfort group when 16 distractors were presented. In Experiment 2, a conscious visual attention task was conducted. No processing-speed advantage was found for migraine groups. In all conditions, the high visual discomfort group performed significantly more slowly than other groups. It was concluded that heightened sensory sensitivity could not explain the processing speed advantage found previously in migraine but may explain the processing speed disadvantage found for the high visual discomfort group. Results are discussed in terms of disordered sustained attention in the high visual discomfort group.