Investigating some critical spatial parameters of text Involved in the judgement of its clarity.

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                      Spatial parameters of text involved                        

                               in judgements of its clarity

Investigating some critical spatial parameters of text Involved in the judgement of its clarity

Illusions observed in striped patterns have been investigated extensively but the origins of perceptual distortions remain unclear. Illusions in striped patterns were first recorded in the last century, with descriptions such as the oscillations of lines, appearing as waves on closer inspection (Purkinje, 1823; pg. 122; cited in Wilkins, 1995), and lines losing their straightness, with the spaces between such lines becoming coloured (Brewster, 1832; pg. 170; cited in Wilkins, 1995).

Patterns of striped lines can induce seizures in patients with photosensitive epilepsy and when these patients view patterns of this kind, epileptiform electroencephalographic activity are often seen (Wilkins, Nimmo-Smith, Tait, McManus, Della Sala, Tilley, Arnold, Barrie & Scott, 1984). When viewing similar patterns of striped lines, individuals not suffering from epilepsy report illusions of colour, shape and motion giving rise to headaches and eyestrain (Wilkins & Nimmo-Smith, 1984).

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Wilkins (1995) observed a 14-year-old girl with epilepsy, who suffered absences only when she was exposed to striped patterns. An electroencephalograph (EEG) was used to determine specific types of pattern that induced the electroencephalographic precursors of seizures.  Further investigation suggested that pattern sensitivity in epilepsy was not as rare as first thought and subsequentially led to studies that determined the stimulus characteristics responsible for the EEG abnormalities in patients with epilepsy (Wilkins et al., 1975, 1979a, 1980, 1981; cited in Wilkins, 1995). The pattern parameters found to increase the probability of epileptiform activity became the basis of research into parameters ...

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