A neural mechanism for detecting object motion during self-motion

Detecting objects that move in a scene is a fundamental computation performed by the visual system. This computation is greatly complicated by observer motion, which causes most objects to move across the retinal image. How the visual system detects scene-relative object motion during self-motion is poorly understood. Human behavioral studies suggest that the visual system may identify local conflicts between motion parallax and binocular disparity cues to depth, and may use these signals to detect moving objects. We describe a novel mechanism for performing this computation based on neurons in macaque area MT with incongruent depth tuning for binocular disparity and motion parallax cues. Neurons with incongruent tuning respond selectively to scene-relative object motion and their responses are predictive of perceptual decisions when animals are trained to detect a moving object during selfmotion. This finding establishes a novel functional role for neurons with incongruent tuning for multiple depth cues.

Human primary visual cortex shows larger population receptive fields for binocular disparity-defined stimuli

The visual perception of 3D depth is underpinned by the brain’s ability to combine signals from the left and right eyes to produce a neural representation of binocular disparity for perception and behaviour. Electrophysiological studies of binocular disparity over the past 2 decades have investigated the computational role of neurons in area V1 for binocular combination, while more recent neuroimaging investigations have focused on identifying specific roles for different extrastriate visual areas in depth perception. Here we investigate the population receptive field properties of neural responses to binocular information in striate and extrastriate cortical visual areas using ultra-high field fMRI. We measured BOLD fMRI responses while participants viewed retinotopic mapping stimuli defined by different visual properties: contrast, luminance, motion, correlated and anti-correlated stereoscopic disparity. By fitting each condition with a population receptive field model, we compared quantitatively the size of the population receptive field for disparity-specific stimulation. We found larger population receptive fields for disparity compared with contrast and luminance in area V1, the first stage of binocular combination, which likely reflects the binocular integration zone, an interpretation supported by modelling of the binocular energy model. A similar pattern was found in region LOC, where it may reflect the role of disparity as a cue for 3D shape. These findings provide insight into the binocular receptive field properties underlying processing for human stereoscopic vision.

Does the Size-Arrival Effect Occur With an Active Collision-Avoidance Task in an Immersive 3D Virtual Reality Environment?

Objective Determine whether the size-arrival effect (SAE) occurs with immersive, 3D visual experiences and active collision-avoidance responses. Background When a small near object and a large far object approach the observer at the same speeds, the large object appears to arrive before the small object, known as the size-arrival effect (SAE), which may contribute to crashes between motorcycles and cars. Prior studies of the SAE were limited because they used two dimensional displays and asked participants to make passive judgments. Method Participants viewed approaching objects using a virtual reality (VR) headset. In an active task, participants ducked before the object hit them. In a passive prediction-motion (PM) judgment, the approaching object disappeared, and participants pressed a button when they thought the object would hit them. In a passive relative TTC judgment, participants reported which of two approaching objects would reach them first. Results The SAE occurred with the PM and relative TTC tasks but not with the ducking task. The SAE can occur in immersive 3D environments but is limited by the nature of the task and display. Application Certain traffic situations may be more prone to the SAE and have higher risk for collisions. For example, in left-turn scenarios (e.g., see Levulis, 2018), drivers make passive judgments when oncoming vehicles are far and optical expansion is slow, and binocular disparity putatively is ineffective. Collision-avoidance warning systems may be needed more in such scenarios than when vehicles are near and drivers’ judgments of TTC may be more accurate (DeLucia, 2008).

Seeing Depth with One Eye and Pictorial Space

In my second post I questioned whether the integration of pictorial cues and binocular disparity occurs at the level of perception. In this third post, I push the argument further by questioning whether pictorial cues contribute to 3D vision at all.

Scaffolding depth cues and perceptual learning in VR to train stereovision: a proof of concept pilot study

Stereopsis is a valuable feature of human visual perception, which may be impaired or absent in amblyopia and/or strabismus but can be improved through perceptual learning (PL) and videogames. The development of consumer virtual reality (VR) may provide a useful tool for improving stereovision. We report a proof of concept study, especially useful for strabismic patients and/or those with reduced or null stereoacuity. Our novel VR PL strategy is based on a principled approach which included aligning and balancing the perceptual input to the two eyes, dichoptic tasks, exposure to large disparities, scaffolding depth cues and perception for action. We recruited ten adults with normal vision and ten with binocular impairments. Participants played two novel PL games (DartBoard and Halloween) using a VR-HMD. Each game consisted of three depth cue scaffolding conditions, starting with non-binocular and binocular cues to depth and ending with only binocular disparity. All stereo-anomalous participants improved in the game and most (9/10) showed transfer to clinical and psychophysical stereoacuity tests (mean stereoacuity changed from 569 to 296 arc seconds, P < 0.0001). Stereo-normal participants also showed in-game improvement, which transferred to psychophysical tests (mean stereoacuity changed from 23 to a ceiling value of 20 arc seconds, P = 0.001). We conclude that a VR PL approach based on depth cue scaffolding may provide a useful method for improving stereoacuity, and the in-game performance metrics may provide useful insights into principles for effective treatment of stereo anomalies.This study was registered as a clinical trial on 04/05/2010 with the identifier NCT01115283 at ClinicalTrials.gov.