ABSTRACT
A unique apparatus recorded eye and head movements of subjects as they tapped or only looked at sequences of 2, 4 or 6 nearby, 3-D targets. Each sequence was repeated 10 times to allow an opportunity for learning. A stereotypical pattern of movements was established after 2-3 repetitions. Subjects almost always looked at each target just before tapping it. Looking-only was more difficult than tapping in that it took more time and, unlike tapping, usually did not benefit from practice. The number of targets in a sequence affected time/target in both tasks. Sequence length and practice effects show that memory was involved. The persistent strategy of looking before tapping and the subjects’ inability to tap a well-learned pattern with eyes closed, show that visual cues were also important We conclude that motor planning occurred first at the level of the task and then at the level of specific motor programs. The relative difficulty of the less natural, looking-only task, in which the eyes worked without a meaningful cognitive or motor purpose, suggests that efficient eye movement programming requires a natural task of the kind eye movements evolved to serve.
