Test Protocols
Sensory Organisation Test (SOT)
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0:00The Sensory Organisation Test consists of six conditions, each repeated three times for a total of eighteen trials. Trials last twenty seconds.
0:14Condition one: eyes open, fixed surface, fixed visual surround. The baseline. All three inputs are reliable.
0:28Condition two: eyes closed, fixed surface. Vision is removed. Somatosensation and vestibular input remain reliable.
0:41Condition three: eyes open, sway-referenced surround. The walls move with the patient — vision is now misleading. Somatosensation and vestibular input remain reliable.
0:57Condition four: eyes open, sway-referenced surface. The floor moves with the patient — somatosensation is now misleading. Vision and vestibular input remain reliable.
1:13Condition five: eyes closed, sway-referenced surface. Vision absent, somatosensation misleading. Only vestibular input remains.
1:28Condition six: eyes open with sway-referenced surface AND sway-referenced surround. Vision and somatosensation both misleading. Only vestibular input remains, but now with two unreliable streams to ignore.
1:47From these six conditions, four sensory ratios are derived. Each isolates one input by comparing performance on the condition that taxes it against the baseline.
2:04The somatosensory ratio is condition two over condition one — how well the patient stands without vision.
2:17The visual ratio is condition four over condition one — how well the patient uses vision when somatosensation is unreliable.
2:32The vestibular ratio is condition five over condition one — pure vestibular reliance.
2:46The visual preference ratio is conditions three and six combined, over conditions two and five combined. It detects pathological over-reliance on vision.
3:05The classical vestibular pattern is selective abnormality on conditions five and six, with intact performance elsewhere. This is the signature of acute peripheral vestibular loss.
Six-condition interactive
The interactive below lets you cycle through every disease pattern in the atlas and see how it manifests across the six SOT conditions. Each card synthesises a 20-second anterior-posterior sway trace from the archetype's mean equilibrium score, with seeded jitter — click New instantiation for a fresh draw of the same pattern.
Equilibrium scores trend downward as conditions become more sensorily challenging. C5 and C6 are the lowest in healthy subjects but remain above device norms. The composite score sits comfortably above the age-matched lower limit.
In this module
- Overview of the SOTFoundation · Trainee · Clinician
- The six conditionsFoundation · Trainee · Clinician
- Equilibrium score calculationTrainee · Clinician
- Composite score and age normsFoundation · Trainee · Clinician
- Sensory analysis ratiosTrainee · Clinician
- Pattern interpretationFoundation · Trainee · Clinician
- Strategy analysis (ankle vs hip)Clinician
Overview of the SOT
The Sensory Organisation Test is the most-used CDP protocol. It consists of six conditions, each repeated for three 20-second trials, for a total of eighteen trials and about 12 minutes of recording time including rest periods.
Across the six conditions, vision is either available (eyes open) or removed (eyes closed), and the support surface and visual surround are either fixed or sway-referenced. The combinations systematically isolate each sensory stream.
The output of each trial is an equilibrium score from 0 to 100, with 100 meaning negligible sway and 0 meaning the patient's sway exceeded the limit of stability — operationally, a fall. The three trial scores per condition, the six condition means, and the overall composite all feed into pattern interpretation.
The six conditions
Condition 1: eyes open, fixed surface, fixed surround. The baseline. All three sensory inputs are reliable; healthy adults score above 90.
Condition 2: eyes closed, fixed surface. Vision removed; somatosensation and vestibular input remain reliable. Most healthy adults still score above 85.
Condition 3: eyes open, sway-referenced surround. The visual surround tracks body sway, making vision misleading. Somatosensation and vestibular input are unaffected. Healthy adults score in the mid-80s.
Condition 4: eyes open, sway-referenced surface. The floor tracks body sway, making somatosensation misleading. Vision and vestibular input are reliable. Scores drop into the mid-70s in healthy adults.
Condition 5: eyes closed, sway-referenced surface. Vision absent, somatosensation misleading. Only vestibular input remains. This is the hardest pure-input condition and the most sensitive to peripheral vestibular loss; healthy adults score in the 60–70 range.
Condition 6: eyes open, sway-referenced surface and surround. Both vision and somatosensation are misleading. Only vestibular input remains, but the patient must also ignore the false visual signal — harder than condition 5 cognitively, though the pure sensory information is identical.
Equilibrium score calculation
The equilibrium score is calculated from the peak anterior-posterior sway during the 20-second trial, expressed relative to the 12.5 degree limit of stability. The standard formula is EQS = (1 − θ_peak / 12.5) × 100, clamped to the [0, 100] range.
If the patient reaches or exceeds the limit of stability — or steps, or relies on the harness — the trial is scored as a fall (EQS = 0). Some clinicians report fall trials separately rather than averaging them into the condition mean, as a single fall in three trials carries different information than three near-falls.
A score of 100 is rarely seen in practice. Even still, healthy subjects sway by 1–2 degrees during quiet stance; 100 would require zero sway, which is non-physiological. Scores in the high 90s are typical for healthy condition 1 and 2 trials.
Composite score and age norms
The composite score is a weighted average across all eighteen trials. It is the single number most often quoted in clinical reports, and it correlates well with global functional balance.
Age-matched lower limits of normal are roughly 70 in young and middle-aged adults, dropping to about 60 by age 75. The exact cut-off depends on the device's normative database — use the one supplied with the system that recorded the test.
A reduced composite is sensitive but non-specific. It tells you the patient has impaired balance, but not why. The condition-level pattern and the sensory ratios carry the diagnostic information; the composite is the summary metric.
Sensory analysis ratios
Four sensory ratios are derived from the SOT conditions, each isolating one sensory stream:
Somatosensory (SOM) = C2 / C1. How well the patient stands without vision, normalised to baseline. Normal values exceed 0.90.
Visual (VIS) = C4 / C1. How well the patient uses vision when somatosensation is unreliable. Normal values exceed 0.75.
Vestibular (VEST) = C5 / C1. Pure vestibular reliance. Normal values exceed 0.60. This is the ratio most often abnormal in peripheral vestibular disease.
Visual preference (PREF) = (C3 + C6) / (C2 + C5). Detects hyper-reliance on vision: a patient who falls when vision becomes misleading even though somatosensation/vestibular input are intact. Normal values are below 0.92. Elevated PREF is supportive of PPPD.
Pattern interpretation
Five canonical patterns emerge from the SOT, named for which conditions are abnormal:
Vestibular pattern: selective reduction on C5 and C6, all other conditions normal. Classical signature of acute peripheral vestibular loss — neuritis, an uncompensated schwannoma, or the acute phase of Ménière's. The most common pattern in vestibular clinic populations.
Visual-vestibular pattern: reduction on C4, C5, and C6 — the conditions in which somatosensation is unreliable. Park and colleagues (2017) found this in about 24% of acute neuritis cases.
Surface-dependent pattern: reduction on conditions with sway-referenced surfaces (C4–C6) but spared performance with reliable somatosensation. Seen in peripheral neuropathy where vestibular function may be normal but somatosensation is unreliable.
Visual preference pattern: PREF ratio elevated, with or without reductions on C3 and C6. Characteristic supportive feature of PPPD.
Aphysiologic pattern: easier conditions paradoxically worse than harder ones (the Cevette inversion), or extreme inter-trial variability, or patterns that don't fit any physiologically-plausible combination. Non-specific; warrants clinical correlation rather than diagnosis.
Strategy analysis (ankle vs hip)
Strategy analysis reports the proportion of corrective effort taken up by ankle versus hip torque during each trial. The system infers this from the shape of the sway trace — slow, smooth sway is ankle strategy; fast, abrupt sway is hip strategy.
Pure ankle strategy approaches 100 in conditions 1 and 2 in healthy adults. As conditions become more challenging, hip strategy is recruited and the score drops. In condition 5 in young healthy adults, strategy scores around 60–70 are typical.
Three abnormal patterns emerge. Premature hip recruitment — low strategy scores even in conditions 1 and 2 — suggests reduced confidence in ankle torque, often from lower-limb pathology or fear of falling. Failure to recruit hip strategy — strategy scores stuck near 100 even in difficult conditions — suggests trunk-control deficits, sometimes seen in cerebellar disease. Co-contraction stiffening, an anxiety-driven pattern, produces high strategy scores with non-physiological sway frequencies and should be flagged separately.