Eye-Movements of Dyslexic Children Reading in Regular Orthography: Exploring Word Frequency and Length Effects

Eye-Movements of Dyslexic Children Reading in Regular Orthography: Exploring Word Frequency and Length Effects Evgenia Hristova (ehristova@cogs.nbu.bg) Alexander Gerganov (agerganov@cogs.nbu.bg) Ekaterina Todorova (e.todorova@nbu.bg) Severina Georgieva (severina.georgieva@cogs.nbu.bg) Central and East European Center for Cognitive Science, Department of Cognitive Science and Psychology New Bulgarian University 21 Montevideo St., 1618 Sofia, Bulgaria Abstract Eye-movements represent a great interest in studying the specificity of the reading difficulties that individuals with developmental dyslexia have. In the present study dyslexic children were pair-matched with control children in a sentence reading task. The children read sentences in Bulgarian – a Cyrillic alphabet language with regular orthography. Target nouns with controlled frequency and length were embedded in the sentences. Eye movements revealed highly significant group differences in the gaze time and the total fixation times, word frequency and word length effects as well as interaction for both frequency and length with the group factor. These results, especially the frequency effect found in the dyslexic children, are discussed in the context of previous studies. Keywords: development dyslexia; eye movements; reading. Introduction Developmental dyslexia is described as a condition found in children as young as 6-7 years that impairs their reading skills, while their IQ, reasoning and communication abilities are intact. Still, there is large variability in both the symptoms that dyslexic children demonstrate and in the experimental findings that give support to several theories explaining the underlying causes for dyslexia (see Vellutino, Fletcher, Snowling & Scanlon, 2004 for a review). Usually, dyslexic children are given non-verbal, phonological or single word reading tasks, which aim to distinguish between different theories. While the rationale behind these experiments is very sound, classical reading experiments are also of great interest. For many years eye movements during reading provide insight into psycholinguistic research. During reading, dyslexic readers exhibit more and longer fixations and a higher percentage of regressions than normal readers. It is still a matter of debate, whether these divergent eye movement patterns of dyslexic readers reflect an underlying problem in word processing or whether they are – as the proponents of the oculomotor deficit hypothesis claim (e.g. Pavlidis, 1981) – associated with deficient visual performance that is causal for dyslexia. It is a well-documented (and undisputed fact) that eye movements of dyslexic readers differ from those of normal readers. During reading, dyslexic readers exhibit more and longer fixations, shorter saccades and a higher percentage of regressions than normal readers (for review, see Rayner, Hutzler, Kronbichler, Jacobs and Wimmer (2006) used a string processing task that imposes the same requirements as reading to visual perception (letter identification) and oculomotor control (moving the eyes in the same pattern as during reading). The task is different from reading as it does not require linguistic or language processing of the visual information beyond letter identification. In the study above the authors found no differences between the eye- movements of dyslexic and normal readers and concluded that differences in eye-movements during reading are not the cause for the impaired performance. Hyona & Olson (1995) also tested the hypothesis that the specificity of eye-movements of dyslexic readers is the cause for their reading difficulties. They found word length and word frequency effects on eye-movement characteristics of dyslexic readers. The conclusion they made was that the eye-movement patterns of dyslexic readers are affected by the properties of the linguistic material encountered during reading and therefore eye- movement patterns of dyslexic readers are reflection of the difficulties these readers have during linguistic processing (and not vice versa). Still, there are few studies of text- or sentence-level reading with dyslexic children. An eye-movement study on reading German text passage found word length effects for both dyslexic and normal readers as well as interaction between the groups (Hutzler & Wimmer, 2004). The words taken from the text passage, however, could not be controlled for possibly confounding factors like predictability and frequency. In a similar task of reading short text passages in Italian, De Luca, Di Pace, Judica, Spinelli and Zoccolotti (1999) found once again strong length effects but much smaller frequency main effect that was marginally significant and did not interact with the group factor. Finally, Hyona & Olson (1995) compared a group of dyslexic children with younger ones and found highly significant word frequency and word length effects