Eye and head coordination in reading: roles of head movement and cognitive control.

Simultaneous recording of eye and head movements during reading revealed that head movements consisted of two components: a modulatory-velocity component coupled to eye saccades, and a constant-velocity component that was independent of eye saccades. Whereas the constant-velocity component increased as subjects repeatedly read the same text, neither the magnitude of the modulatory-velocity component, nor the amplitude of the eye movement, increased. This outcome could be closely simulated when the head movement command was assumed to be stronger, and issued earlier with repeated reading. These results suggest that higher-level processes related to text familiarity modulate eye-head coordination through head movements.