Introduction

The rotational chair test (RCT) is the most natural and most repeatable stimulus we have for the vestibulo-ocular reflex. It earns its place in the modern vestibular battery for three very different reasons — and understanding them is the first step toward reading the curves.

What the rotational chair test is

A subject sits in a motor-driven chair that can be oscillated sinusoidally or accelerated to a constant velocity. The chair is usually inside a light-tight booth, or video-nystagmography goggles occlude vision. The eyes are filmed by an infrared camera; the software extracts the slow-phase eye velocity at each instant and compares it with the chair velocity to produce three principal numbers:

• Gain — peak eye velocity divided by peak chair velocity.
• Phase — the timing of eye velocity relative to chair velocity.
• Symmetry — whether nystagmus is stronger toward one direction than the other.

A second protocol — the step or velocity-step test — measures a fourth quantity, the time constant (Tc), reflecting how long the brain stores rotational signals after the labyrinth has stopped firing Raphan T 2002.

Three reasons RCT exists

1 · It tests both ears at the same time

Caloric testing irrigates one ear at a time. Patients with bilateral peripheral loss can therefore look symmetrically reduced and the diagnosis is easy to miss. RCT delivers a true bilateral stimulus, and the Bárány Society uses an SHA-based threshold (gain ≤ 0.1 at 0.1 Hz) as one of the criteria for bilateral vestibulopathy Strupp M 2017.

2 · It covers the low-mid frequencies caloric cannot

Caloric stimulation acts at roughly 0.003 Hz. The video head-impulse test (vHIT) covers 1–6 Hz. The RCT fills the gap — 0.01–0.64 Hz — which happens to be exactly the band in which everyday head movements live Wang Y 2022.

3 · It is uniquely good at showing compensation

A unilateral peripheral injury produces a caloric weakness that may persist for a lifetime, yet the patient can be entirely asymptomatic. The reason is central compensation: brainstem and cerebellar circuits rebalance resting tone. SHA tracks that recovery beautifully: an early directional preponderance and phase lead first appear and then fade as compensation proceeds ENT & Audiology News editorial. 2015.

Who this atlas is for

This chapter is written for medical students, ENT and neurology trainees, vestibular audiology fellows, and physiotherapists who want to be able to read a chair report and explain it to a patient. Use the sidebar to pick a level — Foundation, Trainee or Clinician — and the more advanced detail will be present where you want it.