# Eye Movement Parameters in Children with Reading Difficulties
## 1 Introduction  
Reading is a complex visuomotor task involving both a precise performance of the visual and oculomotor system when guiding the reader throughout the text, and a success in the principal components of reading, i.e., phonological awareness, phonics, vocabulary, fluency, and comprehension [1]. During reading, the eyes perform continuous movements from word to word called saccades, as well as regressions that are backward saccades aimed to read a previously read part of the text and refixations that are small-amplitude saccades within the same word. In between saccades, a relatively stable eye position called fixation is acquired during which the visual information, i.e., letters and words in reading, is obtained. Fixations usually last about 200-300 ms, but can last longer depending on the text complexity and other parameters [2]. The relation between saccadic eye movement programming and the higher information processes in reading has been widely discussed in the context of how the perceptual, cognitive, and motor systems interact during the reading process [3, 4, 5]. Based on different models of eye movement control in reading, saccadic eye movement programming is considered to be driven either by the completion of the lexical processing of a certainword [6; 7] or by a random timer that initiates saccadic programming independently from the lexical processing [8; 9]. There are other models of saccadic eye movement programming during reading (e.g., SERIF); however, they are out of the scope of the current research. Early reading development is associated with the executive cognitive functions, i.e., shifting attention, inhibition of dominant responses, working memory, and cognitive flexibility, all of which begin to develop in infancy [10; 11; 12]. It has been demonstrated that executive function performance as early as in infancy can be related to reading performance developing later in life [13; 14]. Reading acquisition has also been attributed to a stage-like process during which children learn visual discriminations of letters and words, grapheme-phoneme correspondences and identifying words (orthographic stage) [15]. Different stages of reading development and performance have also been reflected in eye tracking studies, indicating that as reading proficiency increases, shorter fixations, larger-amplitude saccades and less regressions and refixations are observed [16; 17]. Reading patterns in children are also subjected to the language and its orthographic complexity and predictability [18]. Children with reading difficulties not only present with lower reading rates, accuracy, fluency, and reading comprehension [19], but also demonstrate different performance in the objective measurement of eye movements during reading tasks, i.e., higher number of fixations, increased average fixation duration, reduced average saccadic duration, as well as increased total number of saccades and average number of fixations [20; 21; 22; 23; 24; 25]. [PERSON] et al. [26] suggested that the reduced eye movement performance in reading tasks might reflect the comprehension processes in reading. But, since reading is a complex cognitive task involving a precise coordination between the processes of visual perception, attention, phonological awareness and other cognitive processes [27], as well as the oculomotor system guiding the fixation from a word to the next word, the analysis of reading eye movements does not reveal whether the differences in the eye movement performance are related to oculomotor dysfunction or if they serve as an indicator of the cognitive load. [PERSON] [28] proposed that patients with dyslexia present with more corrective saccades in sequential non-reading saccade tasks, and had troubles with maintaining a stable fixation comparing to the control group, therefore indicating that patients with dyslexia might also present with oculomotor dysfunction.