Perisaccadic mislocalization in dyslexia

Evidence from experiments designed to elicit the phenomenon of perisaccadic mislocalization of briefly presented probe stimuli suggests that mechanisms implicated in the planning of a saccade are also implicated in the means by which spatial constancy is maintained across saccades. We postulated that impairments of visual attention observed in dyslexic readers may arise from impairment of mechanisms that also subserve the maintenance of spatial constancy, leading to visual confusion during reading. To test this hypothesis, we compared the performance of adults with dyslexia with that of non-impaired control participants on a task designed to elicit perisaccadic mislocalization. Typically in such tasks, when probes are presented close to saccade onset, mislocalization of all probes, including those presented beyond the saccade target, are mislocalized in the direction of the saccade target, a phenomenon known as perisaccadic spatial compression. In addition, a second tendency, in which all probes are mislocalized in the direction of the saccade itself is referred to as shift. Dyslexic participants showed attenuated perisaccadic compression effects relative to those found in control participants, while the degree to which the reported positions of the probes were shifted in the direction of the saccade did not differ significantly between groups. We propose that compression errors are likely to arise from predictive mechanisms that normally maintain spatial constancy across saccades. Our finding was therefore interpreted as support for the hypothesis that predictive spatial constancy mechanisms may be disrupted in dyslexia.