The time course of top-down control on saccade averaging
J Heeman1, J Theeuwes2, S Van der Stigchel1
1Experimental Psychology, Helmholtz Institute, Utrecht University, Utrecht, The Netherlands.
Vision Research
|April 16, 2014
Summary
The global effect, where eye movements land between nearby objects, is influenced by top-down factors earlier than previously thought. Even for rapid eye movements (saccades), instructions can guide gaze towards a specific target.
Area of Science:
- Neuroscience
- Cognitive Psychology
- Vision Science
Background:
- The global effect describes how eye movements to nearby objects land intermediately.
- This effect is primarily driven by bottom-up, reflexive processes for short-latency saccades.
- Top-down factors are known to modulate this effect at longer latencies.
Purpose of the Study:
- To determine the time course of top-down influence on the global effect.
- To investigate how target instructions affect saccade landing positions.
- To understand the interplay between bottom-up and top-down processing in eye movements.
Main Methods:
- Utilized a standard global effect paradigm with two peripheral stimuli (red and green).
- Manipulated target instructions: no instruction, block instruction, or trial-by-trial variation.
- Measured saccade landing positions in relation to stimulus proximity and latency.
Main Results:
- Without specific instructions, saccades landed between stimuli (classic global effect).
- Target instructions significantly altered saccade landing accuracy.
- Top-down effects were observed even at short saccade latencies (around 200 ms).
Conclusions:
- Top-down processing influences saccade averaging earlier than previously assumed.
- The global effect is not purely reflexive and is susceptible to cognitive control.
- This suggests an early integration of goal-directed information in the saccade generation process.
