Vergence-accommodation conflict: Difference between revisions
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{{see also|Terms|Technical Terms}} | {{see also|Terms|Technical Terms}} | ||
'''Vergence-accommodation conflict''' ('''VAC'''), also known as '''accommodation-vergence conflict''' or sometimes ''' | '''Vergence-accommodation conflict''' ('''VAC'''), also known as '''accommodation-vergence conflict''' or sometimes '''accommodation-vergence mismatch''', is a visual and perceptual phenomenon that occurs when the [[Brain|brain]] receives mismatching cues between the distance to which the eyes are pointed or converged ([[Vergence|vergence]]) and the distance at which the eyes' lenses are focused ([[Accommodation (eye)|accommodation]]).<ref name="Hoffman2008">{{cite web |last=Hoffman |first=D. M. |last2=Girshick |first2=A. R. |last3=Akeley |first3=K. |last4=Banks |first4=M. S. |title=Vergence-Accommodation Conflicts Hinder Visual Performance and Cause Visual Fatigue |journal=Journal of Vision |volume=8 |issue=3 |pages=33 |url=https://jov.arvojournals.org/article.aspx?articleid=2192424 |year=2008}}</ref><ref name="Kreylos2014VAC">{{cite web |last=Kreylos |first=Oliver |title=Accommodation and Vergence in Head-mounted Displays |url=http://doc-ok.org/?p=1602 |website=Doc-Ok.org |date=2014-04-13}}</ref> Because natural viewing conditions tightly couple these two mechanisms, breaking that link is a primary cause of visual discomfort and performance issues in modern [[Virtual reality|virtual reality]] (VR), [[Augmented reality|augmented reality]] (AR), and other [[Stereoscopy|stereoscopic]] 3-D displays, including nearly all mainstream [[Head-Mounted Display|head-mounted displays]] (HMDs).<ref name="Hoffman2008" /> | ||
==Physiological Basis== | ==Physiological Basis== | ||
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* '''[[Accommodation (eye)|Accommodation]]''': The [[Ciliary muscle|ciliary muscle]] adjusts the shape and thus the [[Optical power|optical power]] of the [[Crystalline lens|crystalline lens]] within each eye to bring the image of the target object into sharp focus on the [[Retina|retina]]. This response is primarily driven by retinal blur. | * '''[[Accommodation (eye)|Accommodation]]''': The [[Ciliary muscle|ciliary muscle]] adjusts the shape and thus the [[Optical power|optical power]] of the [[Crystalline lens|crystalline lens]] within each eye to bring the image of the target object into sharp focus on the [[Retina|retina]]. This response is primarily driven by retinal blur. | ||
In natural vision, these two systems are tightly linked through fast, reciprocal neurological signals known as the [[Accommodation reflex| | In natural vision, these two systems are tightly linked through fast, reciprocal neurological signals known as the [[Accommodation reflex|accommodation-vergence reflex]].<ref name="Kreylos2014VAC" /><ref name="Kramida2016">{{cite web |last=Kramida |first=G. |title=Resolving the Vergence-Accommodation Conflict in Head-Mounted Displays |journal=IEEE Transactions on Visualization and Computer Graphics |volume=22 |issue=7 |pages=1912-1921 |url=https://ieeexplore.ieee.org/document/7296633 |year=2016}}</ref> This coupling ensures that the eyes focus at the same distance they are pointed, allowing for clear, comfortable, and efficient vision. Stereoscopic displays disrupt this natural coupling because binocular disparity cues drive the vergence system to the ''simulated'' depth of a virtual object, while the accommodation system is driven by blur cues to focus on the ''physical'' display surface, which is typically at a fixed optical distance.<ref name="Kramida2016" /> | ||
==Causes / Occurrence in Display Technologies== | ==Causes / Occurrence in Display Technologies== | ||
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* '''Focusing Problems''': Difficulty rapidly refocusing between virtual objects at different apparent depths because the natural reflex is disrupted. Users may also experience lingering focus issues or unusual visual sensations after removing the HMD. | * '''Focusing Problems''': Difficulty rapidly refocusing between virtual objects at different apparent depths because the natural reflex is disrupted. Users may also experience lingering focus issues or unusual visual sensations after removing the HMD. | ||
* '''[[Virtual Reality Sickness|VR Sickness]] / Discomfort''': VAC is considered a significant contributor to symptoms like nausea, dizziness, and general discomfort associated with VR/AR use. | * '''[[Virtual Reality Sickness|VR Sickness]] / Discomfort''': VAC is considered a significant contributor to symptoms like nausea, dizziness, and general discomfort associated with VR/AR use. | ||
* '''Reduced Visual Performance''': Measurable degradation in tasks requiring fine depth judgments, reduced reading speed, slower visuomotor reaction times, and increased time required to fuse binocular images.<ref name="Hoffman2008" /><ref name="Lin2022">{{cite web |last=Lin |first=C-J. |last2=Chi |first2=C-F. |last3=Lin |first3=C-K. |last4=Chang |first4=E-C. |title=Effects of Virtual Target Size, Position and Parallax on | * '''Reduced Visual Performance''': Measurable degradation in tasks requiring fine depth judgments, reduced reading speed, slower visuomotor reaction times, and increased time required to fuse binocular images.<ref name="Hoffman2008" /><ref name="Lin2022">{{cite web |last=Lin |first=C-J. |last2=Chi |first2=C-F. |last3=Lin |first3=C-K. |last4=Chang |first4=E-C. |title=Effects of Virtual Target Size, Position and Parallax on Vergence-Accommodation Conflict as Estimated by Actual Gaze |journal=Scientific Reports |volume=12 |pages=20100 |url=https://www.nature.com/articles/s41598-022-24450-9 |year=2022}}</ref> | ||
* '''[[Focal Rivalry]]''': Particularly in AR, the conflict between focusing on a real-world object and a virtual object projected at a different focal distance can make it difficult or impossible to see both sharply simultaneously. | * '''[[Focal Rivalry]]''': Particularly in AR, the conflict between focusing on a real-world object and a virtual object projected at a different focal distance can make it difficult or impossible to see both sharply simultaneously. | ||