Reading twisted text: implications for the role of saccades.

These experiments investigated how the quality of saccadic skill limits the acquisition of visual information during a reading task. Subjects read text in which the spatial pattern of saccades was varied by reversing the order of words in a line, the order of letters in a word, or both. Some of these transformations drastically altered the customary visual appearance of words. To distinguish visual from oculomotor influences on reading, letters, in some conditions, were rotated 180 deg to produce text in which the customary visual appearance of words was destroyed while the order of words and letters remained unchanged. We found that the directional pattern of saccades had relatively modest effects on reading speed under the instruction to read accurately. The size of saccades had large effects on reading speed. Text in which familiar patterns of letters were destroyed, either by changing letter-order or letter-orientation, was read by sequences of small (less than 30') saccades made to look at every letter, or every alternate letter. Separate tests of letter recognition showed that these small saccades were necessary because recognition of letters drops sharply as a function of eccentricity in the absence of familiar letter patterns. Frequent small saccades slowed reading in that durations of the pauses before saccades increased when saccade size fell below 30-60'. We found a similar pattern of increased saccadic latency with decreasing saccade size when subjects used saccades to track a point whose motion mimicked their own reading eye movement patterns. The long latencies before small saccades in the point-tracking task showed that saccadic programming difficulties contributed to the long pause durations before small saccades during reading. The observed difficulty in programming small saccades means that valid inferences about the duration of visual or cognitive processes cannot be drawn from the temporal pattern of saccades unless the relative difficulty and time required to program different spatial patterns of saccades is taken into account.