Interhemispheric coordination is compromised in subjects with developmental dyslexia.

Developmental dyslexics (DDs) and good readers (GRs) were tested on measures of interhemispheric coordination. All subjects (ages 16 to 47) demonstrated normal oculomotor control and visual acuity, prior to testing. Subjects were instructed to track three different point-light source patterns (single stimulus in one hemifield, dual stimuli in one hemifield and a pair of simultaneous, symmetric, bihemifield stimuli [SSBS]), presented in random sequence and arrayed horizontally at +/- 5, +/- 10, and +/- 15 degrees of eccentricity. Tested with unihemifield stimuli, all subjects showed normal saccadic latencies and trajectories. In response to SSBS, all GRs had pronounced directional preference, choosing largely to track one side over the other. In contrast, DDs showed reduced laterality bias (p less than .025). DDs exhibited also significantly longer response latencies to SSBS than to unihemifield stimulation (p less than .01) and differed significantly from GRs (p less than .05).