Data from: Fixational saccade inhibition and pupil dilation during self-paced limb movement preparation

Fixational saccades are modulated in anticipation of several kinds of
stimuli and motor actions, suggesting that they can form an overt marker
of preparatory state. However, no existing work has studied fixational
saccades ahead of spontaneous limb movements in the absence of sensory
stimuli, in order to isolate motor preparation from other anticipatory
processes (e.g., those related to stimulus processing). Here we examined
fixational saccades while participants made self-paced hand and foot
movements. We observed that fixational saccade rate steadily dropped prior
to either kind of motor action, and recovered immediately after. To
examine the relation between this fixational saccade rate signal and other
known signals that precede volitional action, we analyzed how this signal
related to anticipatory pupil size changes in the same dataset.
Replicating previous work, we found steady pupil dilation ahead of limb
movements, followed by rapid re-constriction. The amplitude of this pupil
signal covaried across individual limb movements with that of the
fixational saccade rate signal. The pupil modulations, moreover, followed
too shortly after the accompanying fixational saccade rate modulations to
be caused by saccade-induced changes in visual input. Together, these
observations suggest a joint neural factor influencing both fixational
saccade rate and pupil size ahead of limb movements. We discuss possible
interpretations of our findings, both specific ones that center on
processes of motor planning or temporal expectation, and more general ones
that are in terms effort.