Normal Waves

Before learning what abnormal looks like, the eye has to learn the normal pattern in three sweeps: gain rises with frequency, phase lead decays toward zero, and symmetry stays inside a narrow band.

Gain

Healthy adults show a low-frequency “roll-off”: at 0.01 Hz the gain averages ~0.35 with a normal range from about 0.18 to 0.55, rising to ~0.75 at 0.32 Hz Wang Y 2022. The low-frequency dip is not pathology — it is the cupula's mechanical filter character. The eye catches up at higher frequencies because the canal is now operating well above its corner frequency.

Phase lead

Phase lead is the temporal offset of eye velocity ahead of chair velocity. At very low frequencies eye velocity peaks well before chair velocity (large positive lead, 20–65°). As frequency climbs, the lead shrinks toward zero. A frequency-flat profile near 0° is the signature of a fully working VOR.

Symmetry

Symmetry — sometimes called directional preponderance — compares peak slow-phase velocity in the right-beating versus left-beating phases of each sinusoid. A healthy adult is symmetric to within roughly ±22 %. The arithmetic is borrowed from the Jongkees caloric formula Jacobson GP 2015.

Time constant (step test)

The step-test Tc reflects how long the velocity-storage integrator keeps the VOR firing after labyrinth input has stopped. Normal Tc sits between 12 and 25 s. Shorter Tc (toward the cupula value of ~5 s) indicates peripheral loss; longer Tc (often 30 s or more) suggests cerebellar disinhibition Raphan T 2002.