Temporal coordination of the human head and eye during a natural sequential tapping task

The 'natural' temporal coordination of head and eye was examined as four subjects tapped a sequence of targets arranged in 3D on a worktable in front of them. The head started to move before the eye 48% of the time. Both the head and eye started to move 'simultaneously' (within 8 ms of each other) 37% of the time. The eye started to move before the eye only 15% of the time. Gaze-shifts required to perform the tapping task were relatively large, 68% of them were between 27 degrees and 57 degrees. Gaze-shifts were symmetrical. There were almost as many lefts as rights. Very little inter- or intra-subject variability was observed. These results were not expected on the basis of prior studies of head/eye coordination performed under less natural conditions. They also were not expected given the results of two rather similar, relatively natural, prior experiments. We conclude that more observations under natural conditions will have to be made before we understand why, when and how human beings coordinate head and eyes as they perform everyday tasks in the work-a-day world.