Microsaccade production during saccade cancelation in a stop-signal task

Area of Science:

• Neuroscience
• Ophthalmology
• Behavioral Science

Background:

• Two hypotheses exist regarding neural mechanisms of gaze control: the fixation hypothesis and the microsaccade hypothesis.
• The fixation hypothesis posits that rostral superior colliculus (SC) neurons enforce gaze fixation.
• The microsaccade hypothesis suggests rostral SC neurons encode microsaccades, not fixation itself.

Purpose of the Study:

• To evaluate the fixation and microsaccade hypotheses using behavioral data from a saccade stop-signal task.
• To determine if neural activity in the SC during saccade cancellation leads to increased or decreased microsaccade production.

Main Methods:

• Analyzed microsaccades produced by four monkeys performing a voluntary saccade cancellation task.
• Monkeys received explicit stop signals to cancel partially prepared eye movements.
• Behavioral data on microsaccade production and timing were collected and analyzed.

Main Results:

• Successfully canceled saccades were associated with significantly fewer microsaccades, supporting the fixation hypothesis.
• The microsaccade hypothesis was contradicted, as imbalanced SC activity did not elevate microsaccade production.
• Microsaccades that did occur during successful cancellation were often directed toward the target location.

Conclusions:

• Findings demonstrate that imbalanced activity within the superior colliculus does not necessarily produce microsaccades.
• Evidence suggests that saccade preparation and cancellation are distinct neural processes.
• The study supports the role of SC in enforcing gaze fixation rather than solely encoding microsaccades.