HVS 6D VR Virtual Reality Triangle Completion (Return-to-Home) Task

A fully immersive equivalent of the Triangle Completion Test

The HVS 6D VR system allows researchers to implement a controlled, fully immersive version of the Triangle Completion Test (TCT), also known as the return-to-home task, within a fully immersive and controlled virtual environment.

In this paradigm, participants are guided along two legs of a triangular path and are then required to return directly to the starting point without guidance. This task is used to assess path integration – the ability to update position based on self-motion cues – while minimizing reliance on landmark-based or allocentric strategies common in VR Morris water maze paradigms.

Unlike traditional laboratory versions of the test, which often require blindfolding and physical guidance, the HVS 6D VR implementation allows participants to walk naturally while maintaining experimental control and safety; it automatically analyses behavior and (if required) theta activity.

Natural Movement Without Blindfolding

In conventional triangle completion tasks:

  • Participants are often blindfolded.
  • They may be physically guided along paths.
  • Balance and postural instability can influence results.
  • Anxiety or ataxia may affect performance independently of navigation ability.

In the HVS 6D VR system:

  • Participants walk naturally on the omnidirectional treadmill.
  • The environment can be rendered visually uniform when required, to remove stable visual landmarks and directional reference cues, or optionally to eliminate visual cues entirely.
  • No blindfolding is necessary.
  • The safety rail of the Omnidrive omnidirectional treadmill provides physical stability if needed.
  • The risk of falls or instability is minimized.
  • Quantitative analysis is automatically provided.

This makes the task suitable not only for research participants, but also for:

  • Vestibular patients
  • Older adults
  • Individuals with balance difficulties
  • Neurological or rehabilitation cohorts

Controlled Manipulation of Sensory Inputs

A major advantage of the VR implementation is the ability to control which idiothetic and allothetic cues are available.

The system allows:

  • Full integration of idiothetic cues (vestibular, proprioceptive, efferent) – or controlled exclusion (see below)
  • Controlled inclusion or exclusion of visual (allothetic) cues
  • Isolation of specific sensory contributions

Typical task structure

In a standard version:

  • The first two corners of the triangle are visible targets in the VR environment (either both visible at once, or just the current target visible).
  • Participants walk naturally on the omnidirectional treadmill (or in a physical space that’s larger than the VR environment) toward the first target, and then the second target.
  • For the return-to-start phase, all visual cues are removed.
  • The participant attempts to return to the origin using path integration, stopping when they reach their percieved start-point.
  • This preserves natural locomotion while ensuring that the critical return segment depends primarily on self-motion cues (vestibular, proprioceptive, and motor efference signals), in the absence of visual landmarks or directional references.

Alternative Versions

The system supports multiple variations depending on research aims:

Pure Path Integration (as above)

  • No visual cues during the return phase.
  • Tests integration of vestibular, proprioceptive, and motor efference signals in spatial updating.

Passive Rotation (Externally Driven Angular Updating)

The participant is rotated by external action (e.g., on a rotating chair) rather than initiating head or body turns themselves. The participant is rotated en bloc (head and body together) to stimulate semicircular canals without introducing voluntary motor commands.

  • No efference copy is generated as no voluntary motor command is issued by the participant.
  • Central cancellation mechanisms associated with self-generated movement are not engaged.
  • Visual cues can be included or removed depending on experimental design.

Testing participants with this version as well as the active-turning version, allows you to test:

  • Vestibular angular encoding without efference-copy-based cancellation (semicircular canal-mediated angular encoding).
  • The integrity of vestibular afferent signaling independent of motor prediction.
  • Differences between active and passive vestibular processing.
  • The contribution of efference copy and internal model prediction to spatial updating.
  • Whether vestibular damage primarily affects peripheral encoding or disrupts the accuracy of central predictive (cancellation) models engaged during active motion.

Angular-Only Updating

  • Participants rotate to face successive triangle vertices without walking.
  • Reduces the task to angular spatial updating, emphasizing semicircular canal contributions while minimizing translational proprioceptive cues.

Visual Reference Versions

  • Visual cues remain present throughout.
  • Allows assessment of landmark-based correction of path integration error and recalibration of internal spatial estimates.

Visual vs Vestibular Comparison

  • Compare return performance with and without visual landmarks.
  • Quantify relative cue weighting using precision and variance measures consistent with Bayesian multisensory integration models.

Experimenter Control

Because all environmental features are experimenter-controlled, researchers can precisely define:

  • Path length between each point
  • Required turn angles
  • Visibility conditions
  • Cue reliability
  • Trial sequencing
  • Reduced confounds from postural instability

Experimenters can also control other factors such as whether to use sound, whether to use EEG (e.g. to monitor or analyse theta activity) or whether to incorporate biofeedback.

Precision Measurement and Advanced Analysis

As with the HVS 6D VR Morris water maze, the system provides detailed quantitative measures. These are available for the first and second targets if required (e.g. to identify participants whose performance is affected by ataxia or other difficulties), and for the return from the second target to the start-point/final target, and include:

  • Heading angle error (actual turn angle vs ideal (re)turn angle)
  • Path efficiency ratio (actual path vs ideal (return) path)
  • Proximity analyses indicating closeness to the target during the trial, such as close encounter measures and Gallagher proximity measures
  • End point error – distance and angle
  • Any or all of the above can be used to calculate variability across trials. Optionally we can provide Bias and Precision Analysis, where the system distinguishes between systematic bias and precision in spatial updating. This distinction is important in vestibular research, as peripheral vestibular deficits often increase variability (reduced precision) without introducing consistent directional bias.
    • Bias (accuracy) is quantified as the mean angular deviation from the ideal return vector.
    • Precision is quantified as the trial-to-trial variability of angular error (using circular statistics), endpoint dispersion, and variability in path efficiency.
      This allows investigation not only of accuracy, but of precision and variability, which are critical for understanding vestibular contribution and Bayesian cue integration.
  • EEG monitoring can be included, optionally with analysis of theta activity during navigation.

Reducing Confounds from Postural Instability

Traditional blindfolded walking tasks can be confounded by:

  • Fear of falling
  • Guarded gait
  • Balance deficits
  • Increased cognitive load from instability

The VR treadmill reduces these issues by:

  • Providing a stable walking surface
  • Allowing natural stepping rather than free-space locomotion
  • Availability of safety rail if required

This allows cleaner measurement of navigation rather than balance control.

Translational Applications

The VR triangle completion paradigm is particularly suited for:

  • Vestibular research
  • Aging studies
  • Sex differences in navigation
  • Sensory cue weighting experiments
  • Rehabilitation research
  • Neurological disorders affecting path integration

Because sensory inputs can be manipulated independently, the system supports direct investigation of:

  • Vestibular dependence
  • Visual compensation
  • Internal model recalibration
  • Active vs passive movement effects

Summary

The HVS 6D VR system provides a safe, immersive, and highly controllable implementation of the triangle completion test, allowing researchers to study path integration under natural locomotion conditions while precisely manipulating sensory input.

It combines ecological validity with experimental rigor, enabling controlled dissociation and manipulation of vestibular, proprioceptive, and visual contributions to navigation in both healthy and clinical populations. By comparing active locomotion, angular-only updating, and passive rotation paradigms, the system allows dissociation of translational path integration, angular vestibular updating, and motor-prediction mechanisms, supporting detailed investigation of peripheral vestibular deficits versus central integration impairments.

Please contact us to discuss any other requirements.