The motor programs of monkey's saccades: an attentional hypothesis.

We analyzed the dynamics of saccadic eye movements performed by monkeys in three different conditions: as a part of an ocular motor task, spontaneously when the monkey was alert but not performing a task in ordinary room illumination, and spontaneously when the monkey was alert but not performing a task in total darkness. We found three general classes of saccades: 1) regular-symmetric, in which the rise time of the velocity profile was equal to the falling time; 2) regular-asymmetric, in which the rise time was less than the falling time; 3) irregular, in which there were multiple velocity maxima or inflection points. The monkeys made irregular saccades half the time in the two spontaneous saccade conditions, and almost never during the task. In order to see if the regularity of saccades was an artifact of reward, we then evoked saccades by presenting the monkeys with novel visual and acoustic stimuli to which they made saccades. Such guided saccades to novel stimuli had regular velocity profiles. We suggest that saccades made as a part of attentive behavior differ in their motor programming from saccades made spontaneously in darkness, or saccades made in the light without a purpose relevant to visual behavior.