Reading unspaced text: implications for theories of reading eye movements.

According to current theories of reading, the reader's saccades are guided primarily by spaces between words, clearly the most prominent visual feature in most modern texts. This belief was investigated by recording eye movements with unprecedented accuracy and precision while subjects read spaced and unspaced passages both silently and aloud. Modest increases in fixation durations and decreases in overall reading speed were observed when unspaced texts were read. However, subjects read unspaced texts with the same level of comprehension and percentage of regressions as they read spaced texts. The only global eye movement parameter that changed appreciably when spaces were removed was progressive (rightward) saccade length. Progressive saccades were shorter in unspaced texts. However, unspaced texts were denser and narrower because they were constructed so as to contain the same number of words/line as the spaced texts. This meant that unspaced texts contained more informational characters/degree of visual angle. The observed decrease in progressive saccade lengh tended to be proportional to this increase in text density. Therefore, the number of saccades/line of text remained approximately the same in both spaced and unspaced texts. Furthermore, a detailed examination of local eye movement properties, i.e. where within words the subjects fixated and how many times they fixated words of different lengths, suggested that the same oculomotor strategy was used for reading spaced and unspaced texts. This was true for both silent reading and reading aloud. Thus, a model that could explain reading spaced texts could also explain reading unspaced texts with only a change of a single global parameter, namely, saccade length. We conclude that the current tendency to emphasize spaces as guides to reading eye movements must be reconsidered. Words, not spaces, may serve as the perceptual units that guide the line of sight through the text.