Effects of flicker on reading comfort - Essay Example

Meares in 1980 and subsequently Irlen in 1983 described same set of symptoms induced by reading as visual perceptual disorder known as Meares-Irlen syndrome (MIS) or scotopic sensitivity syndrome (SSS)2,3. Jeanes et al4 reported that this syndrome can be found in 12 percent of general population and 65 percent of dyslexics. Furthermore, Wilkins5 identified these symptoms as ‘visual stress’ and categorised them into somatic such as tired eyes and visuo-perceptual like color, motion or shape illusions.

Another name of this group of symptoms is ‘pattern glare’ that was used by Wilkins and Nimmo-Smith6 because they induced in normal people, who do not have photosensitive epilepsy, when they observed patterns of strips. There are number of parameters to characterise pattern of strips such as the total size, spatial frequency, duty cycle and contrast7. Wilkins et al8 found that the frequency of pattern glare depends on the characteristics of patterns. Similarly, reading text can induce same effects of discomfort because straight lines of text form a pattern of strips5.

The same characteristics of pattern of strips can also determine the effects induced from text. The size of the page contains text excluding the margins corresponds to the size of pattern, the interline spacing represents the spatial frequency, the middle body of written letters excluding ascenders and descenders corresponds to duty cycle, and the contrast of the ink used on the paper besides the thickness and spacing of the words strokes determines the grating contrast7. Thus, text can induce the incidence of pattern glare, which depends on text characteristics.

The book “Visual stress”, by Wilkins5 has a whole chapter to discuss photosensitive epilepsy and the visual stimulation of seizures. Wilkins states that visual stimulation may trigger seizures in 4 percent of patient with epilepsy. In addition, visual stimulation is the only factor to provoke seizures in many