Dissociation of pursuit target selection from saccade execution

Area of Science:

• Neuroscience
• Ophthalmology
• Systems Neuroscience

Background:

• Smooth pursuit and saccadic eye movements are crucial for visual tracking.
• The relationship between target selection for these two eye movement types is not fully understood.
• It remains unclear if saccades can override established pursuit targets.

Purpose of the Study:

• To investigate whether saccades can alter the target selection for ongoing smooth pursuit.
• To determine if smooth pursuit obligatorily follows the stimulus targeted by saccades.
• To elucidate the underlying mechanisms of pursuit and saccade coordination.

Main Methods:

• Primate models were used to study eye movements.
• Microstimulation of the superior colliculus (SC) was employed to evoke saccades.
• Monkeys performed smooth pursuit on a moving target array.
• A distracter stimulus moving in the opposite direction was introduced.
• Eye velocity was measured post-stimulation to assess target selection shifts.

Main Results:

• Saccades evoked by SC stimulation did not significantly alter the selected pursuit target.
• Pursuit velocity changed by less than 10% of the expected value for a complete target switch.
• Observed velocity changes were comparable with or without a distracter, indicating saccade-evoked effects rather than target switching.

Conclusions:

• The motor execution of saccades is insufficient to redirect smooth pursuit.
• These findings support the hypothesis of a shared target selection mechanism for both pursuit and saccades.
• The coordination between saccadic and smooth pursuit eye movements is likely governed by a common selection process.