Interactions between first- and second-order motion revealed by optokinetic nystagmus

Area of Science:

• Neuroscience
• Vision Science
• Oculomotor Control

Background:

• Previous research indicated second-order motion alone is insufficient for driving optokinetic nystagmus (OKN).
• First- and second-order motion cues are known to interact in motion perception.
• The influence of this interaction on eye movement control remained unclear.

Purpose of the Study:

• To investigate the interaction between first- and second-order motion cues in controlling eye movements.
• To determine if second-order motion modifies the oculomotor response to first-order motion.

Main Methods:

• Subjects viewed dynamic random noise carriers for first- and second-order drifting gratings.
• Combinations of first- and second-order motion cues moving in the same or opposite directions were presented.
• Eye movements were recorded using video-oculography to measure optokinetic nystagmus (OKN) gain.

Main Results:

• OKN gain evoked by first-order motion increased with stimulus contrast.
• Second-order motion in the opposite direction attenuated OKN at low first-order contrasts (<15%).
• Co-directional first- and second-order motion enhanced the OKN response.

Conclusions:

• Second-order motion significantly modifies the optokinetic response to simultaneously presented first-order motion.
• The direction of second-order motion relative to first-order motion determines its modulatory effect on OKN.
• This study demonstrates a clear interaction between different motion cue types in oculomotor control.