binocular vision
La binocular vision is capacity what does the human being have of forming images Through the use of both eyes, integrating in a single image the information that comes from each of the eyes separately.
Binocular vision is especially important because thanks to it we are able to increase our campor visual y perceive the depth of the world around us.
binocular vision
La binocular vision is capacity what does the human being have of forming images Through the use of both eyes, integrating in a single image the information that comes from each of the eyes separately.
Binocular vision is especially important because thanks to it we are able to increase our campor visual y perceive the depth of the world around us.
Binocular vision: Perception of space, depth and size
A fact that has always caught the attention of researchers is how the information that is projected on the retina, in two dimensions, is reconstructed again in the brain in three dimensions. The possible answers can be found in the analysis of how information arrives and how it is processed at the retinal level, which we call the analysis of perception and depth cues.
The visual experiences that we have over time are a fundamental point to understand the keys of depth, how we are learning them. When we see an object partially covered by another, we know that this object is behind it, it is the "occlusion key" and we know it, basically because we have learned it with previous experiences.
Three types of depth keys are defined:
- Oculomotrices.
- Monoculars
- Binoculars.
Oculomotor Keys
They are keys based on two fundamental aspects, our ability to detect the position of objects and eye muscle tension at the moment of perception.
The two fundamental information points are the convergence y the accommodation, which guide us on the proximity or distance of objects from us, both passive and dynamic.
Monocular keys
Monocular cues can be seen even with one eye. The most important are pictorial cues, occlusion, relative height, cast shadows, relative size, family size, atmospheric perspective (distant objects are less sharp because air particles blur them), linear perspective, and texture gradient.
Within the monocular calves there are others related to movement, highlighting parallax and elimination, and enhancement.
In the parallax we see that the closest objects pass faster while the distant objects seem to move more slowly. We see this in real life in situations like looking out the window of a car or train. In the following figure we can see the explanation: it is seen as an eye that moves from the 1 position to the 2, the objects that it is looking at, A and B, its projection in the retina, the variation in the fixation point, it is totally different for A, next, where the path is much larger than for B, far, which barely moves with respect to the ocular axis (dotted blue line).
When two surfaces are at different distances, as in the figure below, any lateral movement of the observer causes the surfaces to appear to move relative to each other. The back surface is covered or eliminated by a surface that is in front when the viewer moves in one direction, while the back surface is uncovered or enhanced when the viewer moves in the other direction.
binocular vision
In binocular cues, depth perception depends on both eyes. The convergence of the eyes also enters into binocular cues, the angle of convergence specifies the depth.
The most important element in the binocular key is the disparity of images that are generated in both eyes, because the eyes are 6 cm apart, and therefore see the world from different positions.
In practice we can check it by placing the index finger of the hand in front of us, about 40 cm, and if we now close one eye and then the other, alternately, we have the sensation that the finger moves, moves horizontally . The phenomenon is explained because each eye has a different viewing angle with respect to the finger and is projected in different positions on the retina.
How binocular vision works
Depth perception occurs in two stages, first binocular disparity, that is, the difference between the images of the two eyes, from which this difference is transformed into depth perception or stereopsis.
Stereoscopes allow viewing of relief vision by breaking down the scene into different signals for each eye, using colored or polarized filters. The brain does the same by creating slightly different images in each eye, generated by the different angle of vision that each eye holds. Recall that on the retinal map, each point of the scene is projected onto a point on the retina that corresponds to the same projection point on the retina of the other eye (retinal correspondence), however, these points do not coincide exactly, there are a slight disparity of positions due to the separation of the eyes, to the angles that form the retina of each eye and the object, this is what makes us see in depth, in relief, without getting to perceive a double image.
When the objects are near or far, the disparity of the retinal points of projection of the objects, are separated by distances that exceed the capacity of unification of the brain, ie they are no longer perceived as an object but we see two, it produces double vision, not crossed for distant objects and crossed for the near ones. The line in which the retinal disparity is minimal is known as a horopter and the area in which double vision is not produced is called the Panum area.
To see if the depth was due to monocular cues or to the disparity generated by stereopsis, Bela Julesz created a type of stimuli known as stereograms, based on random points and used in the clinic to study stereopsis in patients .
One of the important questions was how the retinal disparity signals were processed in the brain. Studies of the striated cortex revealed the presence of specific cells in V1 for disparity, they are binocular depth cells or disparity detectors, because they respond better to stimuli with disparate retinal projection, as shown in the following figure, where the bars P and Q are projected in the same region on the LE retina, while in the RE the projections of P and Q are separated by the distance implied by the angle of view of the RE with respect to P and Q. In the LE, with coincident projection of P and Q, neurons of zero disparity are stimulated (b), while the projection of P and Q in the RE, separated, stimulate selective neurons to disparity in V1 (c), responsible for initiating perception in depth.
Latest advances in binocular vision
Currently, cells that are sensitive to disparity have been discovered in V2 and in the dorsal and ventral tracts, up to TM, demonstrating the importance of the perception of stereopsis in daily life. Studies with fMRI showed that when seen in situations of stereopsis, the parietal lobes are activated to a greater degree, where or how, which makes sense because stereopsis is more important when locating an object in the scene.
The specificity of these cells for vision in stereopsis is evidenced by experimental studies in which one eye is deprived of vision (cats and monkeys) and the retinal disparity is eliminated. With the passing of time it is observed that the cells that were activated with disparate stimuli disappear and that these animals were unable to perform tasks in which stereopsis is required (Randolph Blacke and Helmuto Hirsch 1975, and Gregory de Angelis, Bruce Cumming and Willian Newsome 1998).
