Introduction

Today most, but not all, of the languages of the world are read from left to right. Historically, however, we know that sizable populations have read from right to left, as readers of Hebrew, Arabic, Persian, and Urdu do today. In the early stages of development of Greek writing, reading was in boustrophedon, reading alternately lines from left to right and then right to left, the way some modern day computers' printers print. Historically Chinese and Japanese are read in columns from up to down starting in the upper right hand side of the page; only in the modern era has a horizontal direction been preferred. That remains right to left in Taiwan, but has become left to right in the People's Republic of China and in Japan.

Should the thought cross one's mind that reading left to right is more “natural” because most people read that way today, it bears remembering that for centuries after the seventh and eighth century spread of Islamic civilization, the vast majority of the literate world was reading its languages from right to left. Most obviously in the case of modern Chinese there are cultural and political factors that interact in determining reading direction as well.

Laterality studies of bi-directional readers

Before we turn to the cases of reading disturbance in bi-directional readers, it is worth reviewing the laterality literature on healthy bi-directional readers.