Visual constraints in written word recognition: evidence from the optimal viewing-position effect

In this paper we review the literature on visual constraints in written word processing. We notice that not all letters are equally visible to the reader. The letter that is most visible is the letter that is fixated. The visibility of the other letters depends on the distance between the letters and the fixation location, whether the letters are outer or inner letters of the word, and whether the letters lie to the left or to the right of the fixation location. Because of these three factors, word recognition depends on the viewing position. In languages read from left to right, the optimal viewing position is situated between the beginning and the middle of the word. This optimal viewing position is the result of an interplay of four variables: the distance between the viewing position and the farthest letter, the fact that the word beginning is usually more informative than the word end, the fact that during reading words have been recognised a lot of times after fixation on this letter position and the fact that stimuli in the right visual field have direct access to the left cerebral hemisphere. For languages read from right to left, the first three variables pull the optimal viewing position towards the right side of the word (which is the word beginning), but the fourth variable counteracts these forces to some extent. Therefore, the asymmetry of the optimum viewing-position curve is less clear in Hebrew and Arabic than in French and Dutch.