Vergence eye movements signifying 3D depth perception from 2D movies

A sensation of depth can arise from two-dimensional (2D) movies without any stereoscopic depth cue. Depth perception in three-dimensional (3D) space depends on the stability of stereoscopic gaze by vergence – coordinated movement of the two eyes in opposite directions – compensating the misalignment of the retinal images from the two eyes (i.e. binocular disparity) [1]. On the other hand, the oculomotor mechanisms that stabilize stereoscopic gaze and depth perception in 2D movie space remain unclear [2]. Here, we propose a hypothesis that vergence eye movements signifying 3D depth perception persist during prolonged 2D movie presentation without binocular disparity cues. By measuring eye positions while the subject viewed moving random-dot video stimuli, we show that sustained vergence is induced during 30-s exposure to radially expanding 2D optic flow. Moreover, a 2D video movie showing a passenger’s view of a roller coaster induces continuously changing vergence. In the absence of binocular disparity cues, the pictorial depth information within a 5° × 5° gaze window and optic flow in the movie simultaneously and independently influence vergence. The pictorial gaze-area depth information affects vergence mainly in the virtual far space, whereas optic flow robustly affects vergence irrespective of the nearness. These findings demonstrate that vergence serves as a reliable marker signifying 3D depth perception from 2D movies, imposing critical constraints on creation of an effective and safe virtual reality.

► We used 3D and 2D video movie for investigation of vergence eye movement performance.
► We found that vergence was elicited by not only 3D but also 2D movies.
► Optic flow and pictorial perspective cues in 2D movie asymmetrically affect vergence.
► Vergence serves as a reliable marker signifying 3D depth perception from 2D movies.