Anticipatory saccades in sequential procedural learning in monkeys.

1. In a preceding paper we examined the short-term and long-term processes of learning of sequential procedures in monkeys. We now report that the pattern of eye movements changed along with the long-term learning. 2. The monkey's task was to press five consecutive pairs of target buttons (indicated by illumination) in the correct order for every pair, which the monkey had to find by trial and error (2 x 5 task). The whole sequence was called the "hyperset"; each pair was called the "set." 3. Initially, the saccade toward the correct target occurred after illumination of the targets (visually guided saccade). After sufficient learning, the saccade tended to occur before the target illumination (anticipatory saccade). This was true only for the hyperset that had been learned. 4. The likelihood of anticipatory saccade increased gradually over 20-30 days of practice of the particular hyperset. The time course was similar to how the hand learned (button press latency). 5. The monkeys were required to use the same hand for each hyperset throughout learning, except when we asked them to use the opposite hand. The nearly perfect performance due to the extensive practice was then deteriorated by the use of the opposite hand. We found, in addition, that anticipatory saccades became much less frequent. This finding suggests that critical for the skilled performance was the combination of the eyes and the side of the hand that was used for the practice of a given sequence.