The coordination of eye, head, and hand movements in a natural task
Abstract
Relatively little is known about movements of
the eyes, head, and hands in natural tasks. Normal
behavior requires spatial and temporal coordination of
the movements in more complex circumstances than are
typically studied, and usually provides the opportunity
for motor planning. Previous studies of natural tasks
have indicated that the parameters of eye and head
movements are set by global task constraints. In this
experiment, we explore the temporal coordination of eye,
head, and hand movements while subjects performed a
simple block-copying task. The task involved fixations
to gather information about the pattern, as well as visually
guided hand movements to pick up and place blocks.
Subjects used rhythmic patterns of eye, head, and hand
movements in a fixed temporal sequence or coordinative
structure. However, the pattern varied according to the
immediate task context. Coordination was maintained by
delaying the hand movements until the eye was available
for guiding the movement. This suggests that observers
maintain coordination by setting up a temporary, taskspecific
synergy between the eye and hand. Head movements
displayed considerable flexibility and frequently
diverged from the gaze change, appearing instead to be
linked to the hand trajectories. This indicates that the
coordination of eye and head in gaze changes is usually
the consequence of a synergistic linkage rather than an
obligatory one. These temporary synergies simplify the
coordination problem by reducing the number of control
variables, and consequently the attentional demands,
necessary for the task.