Human Factors | Étienne Peillard

Lab — Avatars and embodiment in virtual reality

Wed, 11 Mar 2026 00:00:00 +0000

Overview

In this lab, you will explore how avatars are created, animated, and embodied in Virtual Reality.

Avatars are a central component of immersive systems. They allow users to perceive and interact with virtual environments through a virtual body. However, the design and calibration of avatars can significantly affect embodiment, comfort, and user perception.

In this lab you will:

create and import a humanoid avatar
animate it using VR tracking
experiment with avatar body modifications
evaluate their impact on embodiment and user experience

1 — Avatar Creation

Create or download an avatar using Mixamo.

Go to https://www.mixamo.com
Select a character from the library
Download the character in FBX format

Import the avatar into Unity

Create a new Unity 3D project.
Import the FBX avatar model into the project.
Drag the avatar into the scene.

Configure materials and textures

When importing FBX models, Unity may embed materials and textures inside the model file. Extract them to make them editable.

Select the avatar model in the Project panel.
In the Inspector, open the Materials tab.
Click:

Extract Materials
Extract Textures

Assign the extracted materials to the correct mesh elements if needed.
Assign appropriate textures to the materials (albedo, normal map, etc.) to ensure the avatar looks correct in the scene.
Verify that the avatar is rendered correctly in the scene.

2 — Using the Avatar in a VR Scene

Follow the tutorial available here:

Unity VR Avatar Tutorial

https://immersive-insiders.com/blog/how-to-animate-your-avatar-for-vr-in-unity

⚠️ Note
The original tutorial uses the Ready Player Me API, which has since been discontinued.
Ignore all steps related to Ready Player Me and instead use the Mixamo avatar you imported.

The objective of this part is to:

add the avatar to a VR scene
connect the avatar head and hands to the VR headset and controllers
observe how avatar motion follows user motion.

3 — Inverse Kinematics (IK)

In Virtual Reality, avatars usually do not have full-body tracking.
Most VR systems only track:

the headset (HMD)
the left controller
the right controller

However, the avatar has many joints (shoulders, elbows, spine, hips, etc.).
To animate the full body from only a few tracked points, VR systems use Inverse Kinematics (IK).

Forward vs Inverse Kinematics

There are two main approaches to animate articulated characters.

Forward Kinematics (FK)

In Forward Kinematics, the motion is applied joint by joint.

For example:

shoulder → elbow → wrist → hand

Each rotation affects the following joints.

This approach is commonly used in traditional animation.

Inverse Kinematics (IK)

In Inverse Kinematics, the desired end position of a limb is known.

For example:

the hand should be at the position of the controller.

The system then automatically computes the rotations of intermediate joints:

controller position → hand → elbow → shoulder

IK therefore allows a virtual body to follow user movements even with limited tracking.

IK in VR Avatars

In most VR systems:

Tracked device	Avatar body part
HMD	head
left controller	left hand
right controller	right hand

An IK solver estimates the position of:

elbows
shoulders
torso
sometimes legs

This reconstruction allows the avatar to appear natural even though only a few points are tracked.

Simple Unity IK Example

Unity’s Animator component includes a built-in IK system.

Example:

void OnAnimatorIK(int layerIndex)
{
 animator.SetIKPosition(AvatarIKGoal.LeftHand, leftController.position);
 animator.SetIKRotation(AvatarIKGoal.LeftHand, leftController.rotation);

 animator.SetIKPosition(AvatarIKGoal.RightHand, rightController.position);
 animator.SetIKRotation(AvatarIKGoal.RightHand, rightController.rotation);
}

This code forces the avatar’s hands to follow the position of the VR controllers.

Experiment

When testing your avatar, observe:

how the arms move when you raise your hands
whether the elbows behave naturally
whether body proportions affect IK quality

Body modifications introduced later in the lab may significantly affect the behavior of IK.

Add a mirror

Seeing your avatar from a third-person perspective helps evaluating embodiment.

You can add a mirror in your scene using the following Unity package:

Mirror Package

Place the mirror in front of the player so they can observe their avatar.

4 — Lower Body Animation (Optional)

If you want to go further, you can animate the lower body of your avatar.

Follow the tutorial:

https://immersive-insiders.com/blog/animating-ready-player-me-avatar-lower-body-for-vr-in-unity

Although the tutorial was written for Ready Player Me avatars, the steps should still apply because Mixamo avatars also use a Humanoid rig.

The goal of this section is to:

improve the realism of avatar motion
add basic walking animation
synchronize upper and lower body movement.

5 — Avatar Customization and Body Modification

In the previous section you adapted the avatar to match the user’s body (eye height, head position, etc.).

In this section you will intentionally modify the avatar body to explore how these changes affect:

embodiment
comfort
perception of movement.

Prepare several avatar configurations by modifying parameters such as:

Change avatar scale

avatar.transform.localScale = new Vector3(1.3f, 1.3f, 1.3f);

Modify arm length

Example:

UpperArm_L scale = 1.4
UpperArm_R scale = 1.4

Modify body proportions

Possible variations:

wider body
thinner body
shorter torso
larger head

Create a non-human avatar

Examples:

extremely long arms
oversized head
very short legs

Hybrid avatars

You may also experiment with avatars that remain humanoid but include non-human features:

cat-head humanoid
robotic body
stylized proportions

The goal is to explore how avatar morphology affects user perception and interaction.

6 — Evaluating Embodiment

To evaluate the impact of avatar modifications, conduct a small user study.

Test two avatars:

a normal avatar
a modified avatar

Ask 3-5 participants to experience both configurations.

Questionnaire

Participants rate each statement using a Likert scale from 1 to 7.

Embodiment

I felt as if the virtual body was my body.
The movements of the avatar felt like my own movements.

Agency

I felt that I controlled the avatar.

Comfort

The body proportions felt natural.

Discussion

After the experiment, discuss:

Which avatar modifications were the most disturbing?
Which ones still felt natural?
How do these results relate to proprioception and body perception?

Report

You will submit a short report describing your work.

Your report should include:

Avatar configurations

description of the tested avatar configurations
explanation of how they were implemented in Unity

Questionnaire results

summary of participant responses
comparison between normal and modified avatars

Discussion

Discuss the results in relation to:

embodiment
proprioception
perception of the body in VR

You may also propose explanations for the observed effects.

Course — Cybersickness and comfort in virtual reality

Tue, 10 Mar 2026 00:00:00 +0000

Cybersickness and Comfort in Virtual Reality

Introduction and key design factors

Étienne Peillard

IMT Atlantique — Lab-STICC

Why comfort matters in VR

Virtual reality can provide strong immersion and a compelling sense of presence.
However, VR can also induce discomfort in a significant proportion of users.
Typical symptoms include:
- nausea
- dizziness
- eye strain
- disorientation
- fatigue

Main idea

A VR application is not only judged by what it enables, but also by how comfortable it is to use.

What is cybersickness?

Cybersickness refers to a set of discomfort symptoms induced by exposure to virtual environments.

It is closely related to motion sickness, but with an important difference:

Motion sickness	Cybersickness
caused by physical motion	often caused by visually simulated motion
example: boat, car	example: VR headset

In VR

The user may see motion without physically moving.

Typical symptoms

Common symptoms include:

Nausea
Dizziness
Eye strain
Sweating
Headache
Disorientation
General discomfort

Questionnaires used in research

Simulator Sickness Questionnaire (SSQ)

One of the most widely used tools.

Measures three categories of symptoms:

Nausea
Oculomotor discomfort (eye strain, blurred vision)
Disorientation

Participants rate the intensity of several symptoms after exposure.

Main explanation: sensory conflict

The most common explanation is the sensory conflict theory.

The brain combines information from:

the visual system
the vestibular system (inner ear)
proprioception

Problem in VR

The eyes may signal motion.
The vestibular system may signal no motion.

This mismatch can produce discomfort.

Other complementary explanations

Postural instability

Cybersickness may also appear when users cannot easily stabilize their posture in response to the virtual scene.

Sensorimotor inconsistency

Discomfort can emerge when the environment behaves in ways that do not match the user’s action-perception expectations.

System disconfort

The prolonged use of a VR system can cause physical discomfort due to factors such as:

headset weight
heat
pressure on the face

Important takeaway

Cybersickness is not caused by a single factor. It usually results from a combination of perceptual, motor, and technical issues.

Technical factors

Several technical parameters strongly affect comfort:

Low frame rate
High latency
Tracking instability or jitter
Incorrect camera updates
Visual stutter

Why it matters

The visual scene should react to the user’s head and body movements in a way that is:

fast
stable
predictable

Motion and locomotion factors

Locomotion design is one of the strongest comfort factors in VR.

Often more discomfort	Often more comfortable
continuous joystick locomotion	teleportation
continuous rotation	snap turning
abrupt acceleration	smooth acceleration/deceleration
camera motion not initiated by the user	user-controlled motion

Field of view and visual mitigation

Peripheral visual motion can strongly contribute to discomfort.

A common mitigation strategy

Dynamic FOV reduction during movement:

reduce peripheral motion
keep central vision available
restore full field of view when the user stops moving

This is sometimes called:

tunneling
vignette

Spatial and perceptual consistency

Comfort is also influenced by how coherent the virtual world feels.

Potential issues include:

incorrect world scale
wrong camera height
tilted horizon
camera lag
head bobbing
artificial sway or roll

Key idea

If the VR system violates basic perceptual expectations, discomfort is more likely.

Design guidelines for comfort

Common recommendations for comfortable VR design include:

avoid abrupt acceleration
limit continuous artificial rotation
maintain a stable horizon
preserve correct scale and height
provide stable visual references
reduce peripheral motion during locomotion
prioritize technical stability and low latency

There is no universal solution

A design choice may help some users and disturb others.

Link with today’s practical session

In the TP, you will:

measure a baseline condition
implement at least three independent comfort-related features
test them with participants
compare the results across groups
derive design guidelines from the class dataset

Goal

Understand comfort in VR not only as a theory, but as a design and engineering problem.

Lab — Cybersickness and comfort in virtual reality

Tue, 10 Mar 2026 00:00:00 +0000

The goal of this practical session is to investigate how different design choices in VR influence user comfort and cybersickness.

You will modify an existing VR navigation application, implement several comfort-related features, and evaluate their impact through a small user experiment.

1. Baseline experiment

Start from the Navigation TP project used previously.

Deploy the application on the VR headset.

Use the city navigation task already implemented in the project.

Ask 3 participants to perform the task. Participants must try to activate as many buzzers as possible within 2 minutes, as in the original TP.

After the task, ask each participant to rate their experience using the following scales:

Nausea: 0–10
Dizziness: 0–10
Eye strain: 0–10

Record the results. These results constitute your baseline condition.

You must implement at least three independent features from different categories that can influence comfort in VR.

Each feature must be implemented independently so that it can be activated or deactivated for testing.

Possible features include (you may implement others if relevant):

Motion and locomotion factors

Continuous joystick navigation
Teleportation locomotion
Continuous rotation
Snap rotation (step-based turning)
Rotation speed modification
Abrupt acceleration
Smooth acceleration / deceleration
Navigation speed increase or decrease

Camera and motion behaviour

Camera lag (delay between head motion and camera update)
Head bobbing
Artificial camera sway
Artificial camera stabilization

Field of view and visual factors

Field-of-view reduction during movement (tunneling / vignette)
Dynamic FOV adjustment based on speed
Larger field of view
Smaller field of view

Spatial perception factors

Incorrect world scale
Height offset (camera slightly too high or too low)
Tilted horizon
Slight camera roll

Environmental cues

Adding stable visual references (e.g. cockpit frame or nose)
Removing environmental references
High visual motion in the environment (moving objects)
Static vs dynamic environment

Rendering / visual complexity

Reduced frame rate (simulated)
Motion blur
Increased visual contrast
Reduced visual contrast

Some of these modifications may increase discomfort, while others may reduce it.

3. User testing

For each implemented feature, repeat the same experiment.

Ask 3 participants to perform the same task again.

Important rules:

Participants must not know which modification is active.
Use the same task and duration (2 minutes).
Activate only one feature at a time.

After each condition, participants must rate:

Nausea: 0–10
Dizziness: 0–10
Eye strain: 0–10

Record all results.

4. Shared dataset

Report your results in this shared document.

For each condition include:

the implemented feature
the parameters used
the results for the three participants

This shared dataset will allow the class to compare many comfort factors in VR.

5. Report

Your report must include the following elements.

Implementation

Explain how each feature was implemented:

scripts modified or created
parameters used
technical choices

Illustrations or code snippets can be included.

Results

Present your experimental results:

baseline condition
each modified condition

Compare your results with those obtained by other groups in the shared dataset.

Discuss:

which factors had the strongest impact
whether the effects were expected or surprising

Discussion

Provide personal observations and reflections:

subjective impressions during testing
differences between participants
limitations of the experiment

Discuss possible explanations for the observed effects.

Design guidelines

Based on your experiments and the shared class results, propose at least five design guidelines for improving user comfort in VR applications.

Each guideline should include:

a short description of the recommendation
a brief explanation based on your experimental observations

Human Factors | Étienne Peillard

Lab — Avatars and embodiment in virtual reality

Overview

1 — Avatar Creation

Import the avatar into Unity

Configure materials and textures

2 — Using the Avatar in a VR Scene

3 — Inverse Kinematics (IK)

Forward vs Inverse Kinematics

Forward Kinematics (FK)

Inverse Kinematics (IK)

IK in VR Avatars

Simple Unity IK Example

Experiment

Add a mirror

4 — Lower Body Animation (Optional)

5 — Avatar Customization and Body Modification

Change avatar scale

Modify arm length

Modify body proportions

Create a non-human avatar

Hybrid avatars

6 — Evaluating Embodiment

Questionnaire

Embodiment

Agency

Comfort

Discussion

Report

Avatar configurations

Questionnaire results

Discussion

Course — Cybersickness and comfort in virtual reality

Cybersickness and Comfort in Virtual Reality

Introduction and key design factors

Why comfort matters in VR

Main idea

What is cybersickness?

Typical symptoms

Questionnaires used in research

Simulator Sickness Questionnaire (SSQ)

Main explanation: sensory conflict

Problem in VR

Other complementary explanations

Postural instability

Sensorimotor inconsistency

System disconfort

Important takeaway

Technical factors

Why it matters

Motion and locomotion factors

Field of view and visual mitigation

A common mitigation strategy

Spatial and perceptual consistency

Design guidelines for comfort

Link with today’s practical session

Lab — Cybersickness and comfort in virtual reality

1. Baseline experiment

2. Implement comfort-related features

Motion and locomotion factors

Camera and motion behaviour

Field of view and visual factors

Spatial perception factors

Environmental cues

Rendering / visual complexity

3. User testing

4. Shared dataset

5. Report

Implementation

Results

Discussion

Design guidelines