Fixation Control and Antisaccades in Dyslexia

Abstract

While we are reading our eyes are driven by a combination of visual and linguistic properties of the text and by shifts of attention along the text. These cognitive factors influence the cortical-subcortical brain circuitries that basically control saccade programming. Cognitive strategies and saccade programming determine together how intensively a target is fixated, how efficiently attentional selection processes are working, and where and when the eyes will move next (Vitu et al. 1995). The hypothesis of a basic dysfunction in eye movement control in dyslexia independent of linguistic difficulties has been controversely discussed during the past (Stark et al. 1991). Our studies, however, have shown that the reflexive component of the saccadic system (measured in tasks requiring saccades to suddenly appearing targets) is underdeveloped in many dyslexic subjects (Biscaldi et al. 1998). Since fixation control, i.e. the ability of suppressing reflexive saccades, and voluntary saccade generation were found to develop with different speed in a standard population between 8 and 20 years of age (Fischer et al. 1997), we investigated the control of voluntary vs. reflexive saccades in dyslexics.