Small saccades versus microsaccades: Experimental distinction and model-based unification

Area of Science:

• Ophthalmology
• Neuroscience
• Vision Science

Background:

• Natural vision involves rapid gaze shifts (saccades) and fixations.
• During fixations, the eye exhibits continuous movement, including microsaccades and drift.
• Existing models suggest microsaccades are coupled to preceding drift, potentially distinguishing them from voluntary saccades.

Purpose of the Study:

• Investigate the relationship between microsaccades and preceding drift during a sequential scanning task.
• Differentiate properties of microsaccades from goal-directed saccades.
• Develop and test a mathematical model integrating fixational and goal-directed eye movements.

Main Methods:

• Participants performed a sequential scanning task involving goal-directed saccades and microsaccades.
• Analyzed correlations between microsaccade properties and precursory drift motion.
• Developed and simulated a mathematical model of eye movements.

Main Results:

• Microsaccade properties correlated with preceding drift, unlike goal-directed saccades.
• Goal-directed saccade amplitudes were independent of prior drift epochs.
• Model simulations replicated experimental findings, showing drift-microsaccade correlation but not drift-saccade correlation.

Conclusions:

• Microsaccades and goal-directed saccades exhibit functional differences.
• Both movement types may be part of a unified oculomotor continuum.
• The mathematical model quantitatively describes this continuum.