The role of binocular disparity in rapid scene and pattern recognition

Binocular vision supports the development of scene segmentation capabilities: Evidence from a deep learning model

The application of deep learning techniques has led to substantial progress in solving a number of critical problems in machine vision, including fundamental problems of scene segmentation and depth estimation. Here, we report a novel deep neural network model, capable of simultaneous scene segmentation and depth estimation from a pair of binocular images. By manipulating the arrangement of binocular image pairs, presenting the model with standard left-right image pairs, identical image pairs or swapped left-right images, we show that performance levels depend on the presence of appropriate binocular image arrangements. Segmentation and depth estimation performance are both impaired when images are swapped. Segmentation performance levels are maintained, however, for identical image pairs, despite the absence of binocular disparity information. Critically, these performance levels exceed those found for an equivalent, monocularly trained, segmentation model. These results provide evidence that binocular image differences support both the direct recovery of depth and segmentation information, and the enhanced learning of monocular segmentation signals. This finding suggests that binocular vision may play an important role in visual development. Better understanding of this role may hold implications for the study and treatment of developmentally acquired perceptual impairments.

The impact of retinal motion on stereoacuity for physical targets

In a series of studies using physical targets, we examined the effect of lateral retinal motion on stereoscopic depth discrimination thresholds. We briefly presented thin vertical lines, along with a fixation marker, at speeds ranging from 0 to 16 deg·s^-1. Previous investigations of the effect of retinal motion on stereoacuity consistently show that there is little impact of retinal motion up to 2 deg·s^-1, however, thresholds appear to rise steeply at higher velocities (greater than 3 deg·s^-1). These prior experiments used computerized displays to generate their stimuli. In contrast, with our physical targets we find that stereoacuity is stable up to 16 deg·s^-1, even in the presence of appreciable smearing due to visual persistence. We show that this discrepancy cannot be explained by differences in viewing time, prevalence of motion smear or by high frequency flicker due to display updates. We conclude that under natural viewing conditions observers are able to make depth discrimination judgements using binocular disparity signals that are rapidly acquired at stimulus onset.

Binocular disparity can augment the capacity of vision without affecting subjective experience of depth

Binocular disparity results in a tangible subjective experience of three-dimensional world, but whether disparity also augments objective perceptual performance remains debated. We hypothesized that the improved coding of depth enabled by binocular disparity allows participants to individuate more objects at a glance as the objects can be more efficiently differentiated from each other and the background. We asked participants to enumerate objects in briefly presented naturalistic (Experiment 1) and artificial (Experiment 2) scenes in immersive virtual reality. This type of enumeration task yields well-documented capacity limits where up to 3-4 items can be enumerated rapidly and accurately, known as subitizing. Our results show that although binocular disparity did not yield a large general improvement in enumeration accuracy or reaction times, it improved participants' ability to process the items right after the limit of perceptual capacity. Binocular disparity also sped-up response times by 27 ms on average when artificial stimuli (cubes) were used. Interestingly, the influence of disparity on subjectively experienced depth revealed a clearly different pattern than the influence of disparity on objective performance. This suggests that the functional and subjective sides of stereopsis can be dissociated. Altogether our results suggest that binocular disparity may increase the number of items the visual system can simultaneously process. This may help animals to better resolve and track objects in complex, cluttered visual environments.

Stereoscopic Offset Makes Objects Easier to Recognize

Binocular vision is obviously useful for depth perception, but it might also enhance other components of visual processing, such as image segmentation. We used naturalistic images to determine whether giving an object a stereoscopic offset of 15-120 arcmin of crossed disparity relative to its background would make the object easier to recognize in briefly presented (33-133 ms), temporally masked displays. Disparity had a beneficial effect across a wide range of disparities and display durations. Most of this benefit occurred whether or not the stereoscopic contour agreed with the object’s luminance contour. We attribute this benefit to an orienting of spatial attention that selected the object and its local background for enhanced 2D pattern processing. At longer display durations, contour agreement provided an additional benefit, and a separate experiment using random-dot stimuli confirmed that stereoscopic contours plausibly contributed to recognition at the longer display durations in our experiment. We conclude that in real-world situations binocular vision confers an advantage not only for depth perception, but also for recognizing objects from their luminance patterns and bounding contours.

Orienting of visuo-spatial attention in complex 3D space: Search and detection

The ability to detect changes in the environment is necessary for appropriate interactions with the external world. Changes in the background go more unnoticed than foreground changes, possibly because attention prioritizes processing of foreground/near stimuli. Here, we investigated the detectability of foreground and background changes within natural scenes and the influence of stereoscopic depth cues on this. Using a flicker paradigm, we alternated a pair of images that were exactly same or differed for one single element (i.e., a color change of one object in the scene). The participants were asked to find the change that occurred either in a foreground or background object, while viewing the stimuli either with binocular and monocular cues (bmC) or monocular cues only (mC). The behavioral results showed faster and more accurate detections for foreground changes and overall better performance in bmC than mC conditions. The imaging results highlighted the involvement of fronto‐parietal attention controlling networks during active search and target detection. These attention networks did not show any differential effect as function of the presence/absence of the binocular cues, or the detection of foreground/background changes. By contrast, the lateral occipital cortex showed greater activation for detections in foreground compared to background, while area V3A showed a main effect of bmC vs. mC, specifically during search. These findings indicate that visual search with binocular cues does not impose any specific requirement on attention‐controlling fronto‐parietal networks, while the enhanced detection of front/near objects in the bmC condition reflects bottom‐up sensory processes in visual cortex. Hum Brain Mapp 36:2231–2247, 2015. © 2015 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.