Coordination of eye and head movements during reading.
PURPOSE: There is little information regarding the characteristics of head movements during reading. This study was undertaken to investigate horizontal and vertical head movements during two different reading tasks. METHODS: Head and eye movements were monitored with an infrared pupil and head tracker in 15 subjects during repeated reading of text from an A4-sized card and a card 90 degrees wide. In addition, head and eye movements were recorded in 45 subjects to compare head movement propensity during an A4 text-reading task and a saccadic task of an equivalent gaze shift. RESULTS: During the A4 standard reading task, horizontal and vertical head movements accounted for 4.7% and 28.7% of the gaze shift, respectively. During the 90 degrees text reading, horizontal head movements accounted for 40.3% of the gaze amplitude, and vertical head movements accounted for 28.4%. Horizontal gaze velocities increased significantly on repeated A4 and 90 degrees text readings, as did horizontal head velocities and amplitudes. Reading head movement propensities were significantly smaller than saccadic head movement propensities (P < 0.001). CONCLUSIONS: Head movement strategies are rapidly switched between the A4 and 90 degrees text-reading paradigms. They are minimized during A4 text reading but actively assist the gaze strategy during 90 degrees text reading. Horizontal head movement is reduced during A4 reading compared to the equivalent saccadic task and may be suppressed to improve fixation stability. The results support the view that the head and eye movement system is a highly coupled but extremely flexible system.