Eye-head movement coordination: vestibulo-ocular reflex suppression with head-fixed target fixation

Area of Science:

• Neuroscience
• Ophthalmology
• Vestibular System

Background:

• Clear vision requires stable retinal images, achieved through eye counter-rotation during head movements.
• The vestibulo-ocular reflex (VOR) and optokinetic reflex are crucial for stabilizing gaze.
• Understanding the intrinsic gain of the VOR (VORG) and its modulation is vital for comprehending eye movement control.

Purpose of the Study:

• To investigate the intrinsic gain of the human VOR (VORG) under different visual conditions.
• To determine how VORG is modulated by visual feedback during head movements.
• To compare VORG during fixation of stationary and head-moving targets versus a no-target condition.

Main Methods:

• Recorded eye movements in seated subjects during sinusoidal and transient head rotations around the vertical axis.
• Tested three conditions: total darkness (DARK), earth-fixed target (EFT), and chair-fixed target (CFT).
• Analyzed VORG during the initial 200 ms and subsequent periods to assess reflex and visual influence.

Main Results:

• During transient rotations, VORG was consistently 0.9 +/- 0.15 within the first 200 ms across all visual conditions.
• Beyond 200 ms, VORG remained stable at 0.9 in darkness but adjusted towards 1 (EFT) or 0 (CFT).
• Visual tracking mechanisms (smooth pursuit, saccades) appear to influence VORG after 200 ms to minimize retinal slip.

Conclusions:

• The intrinsic VORG in humans is approximately 0.9 in the absence of visual input.
• Visual feedback plays a significant role in modulating VORG, especially for sustained head movements.
• Observed VORG values in darkness reflect the baseline reflex, while visual conditions demonstrate adaptive gain control.