The CDP battery
Sensory Organization Test
Six 20-second conditions that progressively strip out vision and proprioception, forcing the patient to rely on different combinations of sensory input. The result is a profile of which system the patient depends on, and which has failed.
The SOT is the most-administered CDP test. It works by taking away or distorting individual sensory inputs to expose what the patient is relying on. A patient who falls only on the conditions that isolate the vestibular system has, by inference, a vestibular deficit.
The figure below shows the six conditions and the typical clinical interpretation of each. Conditions 5 and 6 — eyes-closed sway-referenced platform and sway-referenced vision + platform — are the most discriminating for vestibular hypofunction.
Each condition is performed three times for 20 seconds. The score for each trial is the equilibrium score — a 0–100% measure of how much of a theoretical 12.5° anteroposterior sway envelope the patient retains.2The three trials are averaged per condition; the six condition scores combine into a single composite score.
The diagnostic geometry: bilateral vestibulopathy fails 5 and 6 selectively; visual dependency fails 3 and 6 (the conditions where vision is unreliable); somatosensory loss fails 4, 5 and 6 (the conditions where the platform is sway-referenced).3
The model behind the SOT is Peterka's sensorimotor integration account: the central nervous system reweights the gain on visual, vestibular and somatosensory channels in proportion to their perceived reliability, and posturographic profiles can be reproduced by parametric changes in those weights.1This is why the SOT is functional, not anatomic — it measures the weighting, not the lesion.
The strategy score in each condition reports whether the patient is using an ankle strategy (high score) or a hip strategy (low score). A drift from ankle to hip across conditions is normal as the sensory challenge increases; persistent hip-strategy reliance at low difficulty flags compensatory behaviour, fear of falling, or impaired sensory integration.5,4
The six conditions
Click a tile to read the sensory profile and the typical failure pattern. Each glyph animates the patient's sway — note how the platform tilts with the body when sway-referenced, and how the visual surround tilts in SOT 3 and 6.
Reading the equilibrium score
Drag the slider to see how the score collapses as maximum sway approaches the 12.5° stability envelope. The patient figure tilts in real time; the score band changes from normal through critical to a fall.
Increased sway but no fall. Partial dependence on the manipulated sensory channel.
ES = ((12.5° − θmax) ÷ 12.5°) × 100
- Score near 100: patient remains within the stability envelope; balance is well-controlled in that condition.
- Score 60–90: increased sway but no fall; partial dependence on the manipulated channel.
- Score 0–40: large sway approaching the envelope edge; high-risk pattern.
- Score 0: fall — patient stepped or used the harness; the condition exposes a critical deficit.
Sensory reweighting — a live model
Adjust the visual, vestibular and somatosensory reliability sliders to see the centre of pressure trace and approximate equilibrium score change. Try the presets: Eyes closed, Vestibular loss, Neuropathy and Triple losseach reproduce a clinically familiar stabilogram.
Optic flow and horizon cues. Lost: SOT 2 (eyes closed), 5; degraded SOT 3, 6.
Semicircular canal and otolith input. Lost: bilateral vestibulopathy. Critical for SOT 5 and 6.
Proprioception from feet, ankles and joints. Lost: peripheral neuropathy. Critical for SOT 4–6.
Mixed pattern. Sway broadly tracks total available sensory evidence.