A neural correlate for the gap effect on saccadic reaction times in monkey

Area of Science:

• Neuroscience
• Oculomotor control
• Primate vision

Background:

• The gap effect is a phenomenon where saccadic reaction time decreases with a dark interval between fixation point disappearance and target appearance.
• Fixation cells in the monkey superior colliculus are known to inhibit saccadic eye movements and control visual fixation.

Purpose of the Study:

• To investigate the correlation between fixation cell discharge patterns and the gap effect.
• To determine the role of superior colliculus fixation cells in modulating saccadic reaction times during varying temporal gaps.

Main Methods:

• Recording the activity of fixation cells in the monkey superior colliculus.
• Measuring saccadic reaction times during visually guided saccades with manipulated temporal gaps.
• Analyzing the relationship between fixation cell firing rates and gap durations.

Main Results:

• Saccadic reaction times were shortest for gap durations of 200-300 ms.
• Fixation cell activity showed a minimum discharge rate around 200-300 ms into the gap.
• Fixation cell activity increased with target appearance for shorter or longer gap durations.

Conclusions:

• Fixation cell activity in the superior colliculus provides a neural correlate for the gap effect.
• Reduced fixation cell activity during optimal gap durations weakens inhibition on the saccade system, leading to faster saccade initiation.