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The oculomotor gap effect without a foveal fixation point
R Fendrich1, S Demirel, S Danziger
1Program in Cognitive Neuroscience, Dartmouth College, Hanover, NH 03755-3547, USA.
Vision Research
|May 26, 1999
Summary
The gap effect reduces saccade latency when a fixation point disappears before a visual target appears. This effect was observed regardless of fixation anchor type, suggesting involvement of superior colliculus fixation cells.
Area of Science:
- Neuroscience
- Ophthalmology
- Cognitive Psychology
Background:
- The 'gap effect' is a phenomenon where saccade latency decreases when a fixation point is removed prior to target onset.
- Understanding the neural mechanisms underlying the gap effect is crucial for comprehending sensorimotor control.
Purpose of the Study:
- To investigate the influence of fixation anchor eccentricity on the gap effect.
- To explore the role of fixation cells in the superior colliculus in mediating the gap effect.
Main Methods:
- Human participants performed saccadic eye movements to visual targets under three conditions: Gap, 0-Gap, and Overlap.
- Fixation anchors were presented centrally or eccentrically (1, 2, or 4 degrees).
- Saccadic reaction times were measured and compared across conditions and eccentricities.
Main Results:
- Saccadic reaction time was significantly reduced in the Gap condition compared to the 0-Gap condition across all fixation anchor eccentricities.
- The 0-Gap condition did not show a reaction time reduction compared to the Overlap condition when fixation anchors were at 2 or 4 degrees eccentricity.
- These findings suggest a partial mediation of the gap effect by fixation cells in the superior colliculus.
Conclusions:
- The gap effect is a robust phenomenon influencing saccade initiation.
- Fixation anchor eccentricity plays a role in the manifestation of the gap effect.
- Superior colliculus fixation cells are likely involved in the neural circuitry underlying the gap effect.