Locomotor sensory organization test: a novel paradigm for the assessment of sensory contributions in gait

Abstract

Feedback based balance control requires the integration of visual, proprioceptive and vestibular input to detect the body's movement within the environment. When the accuracy of sensory signals is compromised, the system reorganizes the relative contributions through a process of sensory recalibration, for upright postural stability to be maintained. Whereas this process has been studied extensively in standing using the Sensory Organization Test (SOT), less is known about these processes in more dynamic tasks such as locomotion. In the present study, ten healthy young adults performed the six conditions of the traditional SOT to quantify standing postural control when exposed to sensory conflict. The same subjects performed these six conditions using a novel experimental paradigm, the Locomotor SOT (LSOT), to study dynamic postural control during walking under similar types of sensory conflict. To quantify postural control during walking, the net Center of Pressure sway variability was used. This corresponds to the Performance Index of the center of pressure trajectory, which is used to quantify postural control during standing. Our results indicate that dynamic balance control during locomotion in healthy individuals is affected by the systematic manipulation of multisensory inputs. The sway variability patterns observed during locomotion reflect similar balance performance with standing posture, indicating that similar feedback processes may be involved. However, the contribution of visual input is significantly increased during locomotion, compared to standing in similar sensory conflict conditions. The increased visual gain in the LSOT conditions reflects the importance of visual input for the control of locomotion. Since balance perturbations tend to occur in dynamic tasks and in response to environmental constraints not present during the SOT, the LSOT may provide additional information for clinical evaluation on healthy and deficient sensory processing.

Figure 1

The SMART balance Master (NeuroCom International Clackamas, OR, USA) is used to perform the Sensory Organization Test (SOT). This test contains six conditions: 1) eyes open with fixed surface and fixed visual surrounding; 2) eyes closed with fixed surface; 3) eyes open with fixed surface and sway-referenced visual surroundings; 4) eyes open with sway-referenced surface and fixed visual surroundings; 5) eyes closed with sway-referenced surface; 6) eye open with sway-referenced surface and visual surroundings.

Figure 2

The components of Locomotor Sensory Organization Test (LSOT): virtual reality and the instrumented treadmill.

Figure 3

The six conditions of Locomotor Sensory Organization Test (LSOT) that mirrors those of the SOT: 1) normal walking condition 2) Reduced visual condition by reducing vision capability condition 3) Perturbed visual condition by manipulating optic flow speed condition 4) Perturbed somatosensory condition by manipulating treadmill speed condition 5) Perturbed visual and somatosensory condition by reducing vision capability and manipulating treadmill speed condition and 6) Perturbed visual and somatosensory condition by manipulating optic flow and treadmill speed condition.

Figure 4

The netCOP sway area was composed by two-triangle areas that are represented as the areas with dashed lines. Five points was used to generate these two-triangle areas as following: intersection point, right heel-strike, right toe-off, left heel-strike, left toe-off.

Figure 5

Representative trials from a single subject from the six SOT conditions -- the COP sway in the six conditions for the SOT during standing.

Figure 6

Representative trials from a single subject from the six LSOT conditions -- the netCOP sway in the six conditions for the LSOT during walking.