Certain patterns of stripes are judged to be unpleasant to look at. They induce illusions of colour, shape and motion that are sometimes perceived predominantly to one side of fixation. People who suffer frequent headaches tend to report more illusions, and if the pain consistently occurs on the same side of the head the illusions tend to be lateralized. The parameters of the patterns that induce illusions (including their shape, spatial frequency, duty cycle, contrast and cortical representation) closely resemble those that elicit epileptiform electroencephalographic abnormalities in patients with photosensitive epilepsy. The viewing conditions under which such abnormalities are likely to appear are also those under which more illusions are seen.

It is well established that generalized epileptiform EEG discharges unaccompanied by overt clinical change may nevertheless be associated with transitory cognitive impairment (TCI) detectable by appropriate psychological testing. However, the tests employed in most research studies of this phenomenon are of little use for routine clinical application. They are suitable for administration only over short periods of time and are therefore applicable only to patients with a high discharge rate, a serious limitation, as the discharges are generally depressed by the tests themselves. We have developed two short-term memory tasks, one using verbal, the other nonverbal material presented in the form of television games which patients are generally prepared to perform for up to an hour or longer. Forty-six patients with subclinical EEG discharges have been studied. They were screened by video monitoring before and during testing to exclude any with overt clinical changes during the discharges. Despite this rigorous selection, in 50 per cent TCI was demonstrable with a confidence level (within the individual patient) of 10 per cent. Discharges during stimulus presentation were most disruptive of performance and those confined to the period when the patient was responding were without demonstrable effect. A significant association was found between the laterality of focal or asymmetrical generalized discharges and impairment of one or other task, left-sided discharges being associated with errors in the verbal task and right-sided with impairment of the nonverbal test. Two case histories are cited illustrating patients who were clearly handicapped by TCI and whose functioning improved when the subclinical discharges were suppressed by medication. To determine how many patients suffer such disabilities or can be helped by appropriate medication, further prospective studies are required.

Summary:Purpose: This report summarizes background material presented to a consensus conference on visually provoked seizures, convened by the Epilepsy Foundation of America.Methods: A comprehensive review of literature was performed.Results: Photosensitivity, an abnormal EEG response to light or pattern stimulation, occurs in ∼0.3-3% of the population. The estimated prevalence of seizures from light stimuli is ∼1 per 10,000, or 1 per 4,000 individuals age 5-24 years. People with epilepsy have a 2-14% chance of having seizures precipitated by light or pattern. In the Pokemon cartoon incident in Japan, 685 children visited a hospital in reaction to red-blue flashes on broadcast television (TV). Only 24% who had a seizure during the cartoon had previously experienced a seizure. Photic or pattern stimulation can provoke seizures in predisposed individuals, but such stimulation is not known to increase the chance of subsequent epilepsy. Intensities of 0.2-1.5 million candlepower are in the range to trigger seizures. Frequencies of 15-25 Hz are most provocative, but the range is 1-65 Hz. Light-dark borders can induce pattern-sensitive seizures, and red color also is a factor. Seizures can be provoked by certain TV shows, movie screen images, video games, natural stimuli (e.g, sun on water), public displays, and many other sources.Conclusions: Recommendations on reducing risk of seizures have been developed by agencies in the United Kingdom, Japan, and the International Telecommunications Union, affiliated with the United Nations. The Epilepsy Foundation of America has developed a consensus of medical experts and scientists on this subject, reported in an accompanying work.

We find that the ratings of discomfort from a wide variety of images can be predicted from the energy at different spatial scales in the image, as measured by the Fourier amplitude spectrum of the luminance. Whereas comfortable images show the regression of Fourier amplitude against spatial frequency common in natural scenes, uncomfortable images show a regression with disproportionately greater amplitude at spatial frequencies within two octaves of 3 cycles per degree. In six studies, the amplitude at this spatial frequency relative to that 3 octaves below explains variance in judgments of discomfort from art, from images constructed from filtered noise and from art in which the phase or amplitude spectra have been altered. Striped patterns with spatial frequency within the above range are known to be uncomfortable and capable of provoking headaches and seizures in susceptible persons. The present findings show for the first time that even in more complex images the energy in this spatial frequency range is associated with aversion. We propose a simple measurement that can predict aversion to those works of art that have reached the national media because of negative public reaction. Keywords photophobia; visual stress; art appreciation; image analysisIt is known that certain geometric patterns, most notably those of stripes with a spatial frequency close to 3 cycles per degree, can induce seizures in patients with photosensitive epilepsy (Chatrian et al., 1970;Wilkins, 1995), and discomfort in others (Wilkins et al., 1984), particularly individuals with migraine (Marcus and Soso, 1989). Stripes with sinewave luminance profile and square-wave luminance profile, and patterns comprising the first and third Fourier components of a square-wave pattern in triangular or square-wave phase are all capable of inducing seizures when the fundamental spatial frequency is close to 3 cycles/degree (Soso et al., 1980). We show for the first time that the discomfort experienced in response to more complex images can be predicted from their Fourier components, including complex images from non-representational contemporary art or created from filtered noise, and even representational images: photographs of urban and rural scenes.Our investigation was prompted by concern over the complaints with which contemporary art is sometimes associated. In 1971 when an exhibition of Op art was held in London, the Daily Telegraph reported that the guards complained of headaches and were issued with dark glasses. In 1989, the front page of the Sunday Observer carried the story of a newspaper advert with swirling stripes that had been banned after it evoked seizures. In 2005, when a London hospital commissioned artwork and three members of staff complained of migraines in consequence, the resulting controversy reached the national Correspondence should be addressed to: Professor Arnold Wilkins, Department of Psychology, University of Essex, Wivenhoe Park, Colchester, CO4 3SQ, UK, tel +441206872381, fax +441206873590, email arnold@esse...

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