Abstract
Stereo 3D (S3D) is becoming increasingly commonplace in cinema, television, gaming, and elsewhere. S3D viewing is known to cause visual discomfort and fatigue. Conflicts between vergence and accommodation are one source of such symptoms. We measured the combinations of vergence and accommodative stimuli that yield comfortable S3D viewing. We also examined whether the two standard optometric measures used in prescribing optical corrections predict the comfortable combinations for S3D. In the first two experiments, we used a volumetric display to manipulate vergence and accommodative stimuli independently. Experiment 1 examined the effect of viewing distance. For three base distances (0.4, 0.77, and 10 m), we assessed discomfort induced in cues-consistent and -inconsistent conditions. In consistent conditions, the vergence and accommodative stimuli were always equal and they changed in unison from one stimulus presentation to another. In inconsistent conditions, the accommodative stimulus was fixed while the vergence stimulus changed as in the consistent conditions; the latter condition thereby created the vergence-accommodation conflict associated with S3D viewing. The conflict was always crossed (vergence stimulus nearer than accommodative stimulus). Experiment 2 investigated how the sign of the conflict affects discomfort. Using the same base distances, we fixed the accommodative stimuli and changed vergence stimuli in the crossed and uncrossed directions: respectively closer and farther than the accommodative stimulus. The results showed that the comfort zone narrows with increasing distance and that crossed disparities are better tolerated at long distances and uncrossed at near distances. In Experiment 3, we used a phoropter to measure each subject's phoria and relative vergence range. The phoria and range measurements were significantly correlated with discomfort reported in Experiments 1 and 2, which means that these standard clinical measurements can predict the conditions in which subjects will experience discomfort and fatigue when viewing S3D.