Perceptual Cues in the Interaction Between the Vestibulo Ocular Reflex and the Optokinetic Nystagmus in Virtual Reality Environments

Background: We studied the optokinetic nystagmus (OKN) with an optokinetic stimulation (OKs) presented on virtual reality goggles were the stimulus velocity (from the subject’s perspective remaines unchanged. We explored the eye movements and the perception of the OKs velocity while the head moved from side to side. If the OKN is purely dependent on the OKs, head movements should affect neither perception nor eye movements and we ought to see a classic OKN.

Methods: 10 healthy subjects (mean age 22.5, std 2.4) wore an eyetracking system and over it a virtual reality optokinetic stimulation. Pace of head movements was set by a metronome (0.5Hz) and subjects were instructed to move the head from side to side (around 90 degree total movement) in a smooth and velocity-constant movement.

Results: When the OKs direction was Left to Right, 80% of the subjects indicated that the OKs velocity was slowing down when the head moved towards the left and 20% reported that the OKs velocity did not change. When the head moved towards the right, 70% perceived it as moving faster and 30% as not changing velocity.

When the OKs direction was Right to Left, 80% of the subjects indicated that the OKs velocity was faster when the head moved towards the left and 20% that the OKs velocity did not change. When the head moved towards the right, 70% perceived it as moving slower and 30% as not changing velocity.

The number of the fast phase of the OKN with the same stimulus and opposite head movements, was significantly different for both OKs Left to Right (p=0.001) and OKs Right to Left (p<0.001).

Conclusions: The perceptual differences of OKs velocity can be attributed to different eye movements and these eye movements can be explained by simultaneous activation of the VOR and OKN.