Vergence eye movements during fixations in reading.

The purpose of this explorative study was to examine vergence eye movements during fixations in reading. Eye movements of twelve normal adults were assessed during reading of different materials, that is, words within context (prose passages) and words without context (word lists), as well as during different tasks, that is, reading while attending to the meaning and reading while attending to the sound (words had to be pronounced subvocally). Results indicated that vergence velocity was higher during the reading of prose than during the reading of word lists as well as higher during reading for meaning than during reading while subvocalizing. These findings were also true if only the initial 80 ms of each fixation were measured. Post-hoc analyses indicated that the effects of text type and reading objective were partially, but not entirely, attributable to differences in saccade sizes. Findings are taken to suggest that the increase in vergence velocity results from readers attending to larger units of the text.