VR & body perception

Dr Naylor

Size-weight illusions (SWI) (Buckingham, 2019)

• we experience our environment by combining our sensory inputs w/expectations derived from prior knowledge

• can lead to surprising perceptual effects

  • e.g small object feels heavier than larger

• the way an object’s volume is experienced affects the strength of illusion, e.g haptic cues

what we do know about the Size-weight illusion

• top-down influence

  • expectations shape the interpretation of sensory information 

• Haptic SWI is stronger than visual SWI when isolating senses

why should we study Size-weight illusion

• experiments often rely on removing one sense to investigate the other

• remains unclear how the interaction between the senses can impact top-down influences

Size-weight illusion (Buckingham, 2019) study

• recreated SWI in VR

• P judge the heaviness of identical weighted cylinders in 3 conditions:

  • different appearance/same size

  • same appearance/different size

  • different size/appearance.

• confirmed that SWI can be induced in VR

• haptic/tactile cues induce a larger SWI than visual size cues

• even vision & touch cues match → SWI is stronger

• expectations impact which sense is relied on 

material-weight illusion (MWI) (Naylor, 2021)

• low-density-looking materials feel heavier than equally weighted high-density-looking materials because of learned expectations about material–weight relations

  • top-down driven = heaviness perception is shaped by expectations

• P lifted real cubes while seeing virtual cubes in VR

  • mismatched or matched material/weight & tactile/visual

  • all weighed exactly the same 

material-weight illusion (MWI) findings (Naylor, 2021)

• P lifted RL cubes while seeing VR cubes

  • mismatched/matched materials/weights & tactile/visual info

  • all weighed same

• tactile cues induce a stronger illusion than visual cues

• trust the sense of touch more

• no extra effect of combined multisensory cues

  • disregard visual for touch

• conflicting visual expectations are ignored in favour of haptic info

• expectations about a material's typical density override immediate sensory feedback

• both visual & tactile cues can drive MWI but when they disagree → tactile expectations

  • produce a more robust illusion than visual cue alone in every multisensory context

Benefit of using VR in body perception studies 

• Precise control & easy modification to investigate specific questions

• Clarify relative role of each modality whilst retaining ecologically valid sensory experience

• Ability to precisely alter the conflict between multisensory cues to understand interaction

Complex Regional Pain Syndrome (CRPS)

• chronic pain condition occurring after trauma to a limb 

• 70–90% report distortions in how their affected limb looks or feels (size, shape, position, colour, definition, etc.), and these disturbances correlate with pain and symptom severity.

Body perception disturbances (BPD) in CRPS

• common feature of CRPS

• those affected often express altered perceptions, thoughts, & feelings about their affected limb

• patients are reluctant to look at their affected limb

  • avoid it, cover it or ask to amputate

• variability in types of disturbance & lack of diverse treatment

Body perception/representation

• Creating a cohesive representation of our bodies requires the integration & processing of multimodal sensory perceptions

  • both the peripheral and central nervous systems

• different representations for different tasks

• can be inaccurate to the actual physical state of the body 

VR body perception study w/CRPS (Naylor, 2025)

• built VR tool where p w/upper-limb CRPS can sculpt a virtual hand to match:

  • what a normal hand looks like to them

  • how their current hand feels

  • how they want it to be

• 4 p w/CRPS used it and could accurately recreate their strange, very individual distortions (e.g. missing segments, warped fingers) and their preferred “desired” hand.

• some wanted a normal-looking hand, others wanted one that matches their distorted feeling, even if it looks abnormal.

• tool was acceptable, usable, & helped them explain their experience

• supports creating fully personalised, graded VR interventions for body perception disturbances in CRPS.

• abilty to personalise hand enabled them to resolve their issues on a embodied and personal level

value of VR tool for body percpetion for P w.CRPS

• Personalised

  • ability to tailor hands according to P needs was central to success

• Dynamic & embodied

  • Creating real-time changes to the hands

    • quickly & intuitively

    • embodiment necessary for them to address their hand in therapy

• Unbound by reality

  • make changes that would otherwise not be possible in the RW

  • can tailor to specific disturbances with limited constraint

Participant examples

P A

• Said their perception was normal, but didnt like their hand

• affected hand was larger in distortion

P B

• was unable to straigten fingers but when visual was removed, they could

P C

• didnt want to see a normal hand, wanted normal colour but have the hand match the perception 

Clinical application of VR

• Neuropsychological conditions, pain, stroke, DCD, OCD etc.

• Rehabilitation in a safe, controlled environment

• Communication and diagnostic tool

• Research tool to understand underlying mechanisms

• Engagement and distraction

Occupational application of VR

• Develop solutions to tackle occupational issues such as stress and absenteeism in frontline services e.g. police and NHS

Training application of VR

• Simulate environments to practice skills

  • e.g. surgical training

should we be substituting our reality w/VR

• control & precision

• ecological validity

• multidimensional & streamlined data

• unbound by laws of reality

concerns about substituting our reality w/VR

• fundamentally different interface

• artificial ecological validity

• hardware & expertise

• physical discomfort

• privacy & security 

When should we use VR

• when physical reality fails you.

• That is, ‘because we can’ is not a good enough reason to use VR