Rebollo, I. 1 , Aparici, M. 2 & Maiche, A. 1
1 Center for Basic Research in Psychology, School of Psychology, Universidad de la República
2 Universitat Autónoma de Barcelona
The cognitive causes of developmental dyslexia are yet a matter of debate. Recent studies have challenged the phonological theory of dyslexia as the only cause of the reading difficulties; suggesting deficits in balance, motor control, and low level sensory and attentional processing. These deficits are supported by anatomical evidence that shows that dyslexic brain has anomalies in the Cerebellum, Corpus Callosum, Thalamus, and Perysilvean cortex. This study focuses on the visuoatentional deficits that occur in dyslexia. These consist of difficulties integrating and correctly identifying fast sequences of stimuli. Two different hypotheses have arisen in order to explain this deficit. The Visual Attention Span Deficit hypothesis suggests that dyslexics have deficits in the amount of distinct visual elements that can be processed in parallel. On the other hand, the Sluggish Attentional Shifting hypothesis suggests that dyslexics have difficulties in moving the attentional focus between the different elements of a series. The two deficits may interact and co-occur among deficits in different domains. We asked a group of dyslexics university students to compare two strings of eight unknown characters (Arabic) and look for differences. The strings differed in whether there was a difference or not, and in the position where the difference was. Dyslexics were significantly slower than controls, while maintaining the same performance level than controls. The differences in reaction times between dyslexics and controls increased as the differences between the stimuli occurred later in the character strings. Both controls and dyslexics show a crowding effect near the middle and the end of the string, but these effects seems to hamper dyslexic participants performance significatively more than controls. These results cannot be explained by a phonological or lexical processing deficit, since this characters are completely unknown to the participants and thus no phonological information is activated while performing the task.