Binocular coordination during reading

The chapter reviews a range of evidence that suggests that the fixation positions of the two eyes are not perfectly coordinated during reading, such that fixation disparity is frequently observed. The chapter focuses on three critical issues. First, evidence is reviewed for whether the visual or linguistic characteristics of text can influence binocular coordination. Second, a possible link between developmental factors and binocular coordination is discussed (that is, whether children show different patterns of binocular coordination compared to adults). Third, evidence for and against the possibility that dyslexia might be associated with differences in binocular coordination is assessed. On the basis of the existing evidence we conclude that: fixation disparity is, at most, minimally affected by linguistic processing demands; that binocular coordination develops with age such that by the age of 12 children display patterns of binocular coordination equivalent to that of adults; and that the issue of a possible link between binocular coordination and dyslexia demands much further research. The conclusions also highlight the implications of these findings for our understanding of word processing mechanisms, eye movement control during reading, and research with dyslexic readers.