Berkeley He alluded to the difficulty of perceiving the world in three dimensions, since we really see the world in two dimensions. Classically two approaches have been proposed:
Innatist: The perception of three-dimensionality is possible because the organism is ready for three-dimensional perception to occur. Empiricist: We are not genetically prepared, it is our experience with reality that allows this. These two approaches agree that it works by cues, capturing retinal formation data to construct three-dimensionality.
Binoculars (Stereopsis): The visual fields of each eye are overlapping. We see practically the same field of vision, but with a different point of view. Exists cross disparity when the arrangement of objects changes depending on whether you look with one eye or the other. If we draw an imaginary circle that passes through the observer and the object, the objects located on its perimeter produce the same projection on the retina, then the disparity is 0. The proof that disparity exists is found in the stereoscope.
With this system the 95% of subjects perceive three-dimensionality, 5% remaining are stereoblind. There are two theories to explain this: Sherrinton Theory: A series of processes are carried out for each image. It consists of identifying and locating the objects present in the image, and then carrying out the assembly. Until that moment the images used were real objects. This theory is not maintainable, since there are stereopsis with unidentifiable objects such as stereograms of random points. Marr’s theory: The problem of constructing information is finding the correspondence between the two retinal images. The best way to solve the problem is to reduce the complexity of the image with filtering, which consists of eliminating certain spatial frequencies. At the end of the process the points are perfectly identified.
People unable to see stereograms have that birth defect, they only use the information from one eye. Therefore, the neurons responsible for calculating disparities lose their function. The binocular rivalry effect occurs when competitive information is presented to each eye. Then only one pattern is perceived at a time, both can be perceived but alternatively. b) Monoculars (Pictorial): They are called that because they are usually used by painters to give a sensation of depth. Static: In the visual abyss what is produced is a gradient of surface texture, the change in that gradient makes us perceive depth. The relative height is linked to the concept of a line on the horizon, it is measured by the distance to it. Size helps us calculate the distance even when the object is presented out of context if it can be compared with other objects in the scene. The familiarity of the object makes its image on the retina useful for calculating the distance. If the object is not familiar, it is not possible, unless it is presented together with another familiar object.
Gruber and Dimertein (1965) They placed the subjects in a very long hallway where they controlled the lighting. A square was placed at 8 meters and another double size at 16 meters. With illumination they saw that the furthest one was the greatest. Then they were presented with no light in the hallway and two squares of equal size were perceived at the same distance. Familiarity is insufficient.
In the Ames room, a room with peculiar characteristics, in which the distance between the ceiling and the floor is different depending on the area, the effect that we can perceive is that an adult is smaller than a child. Interposition or occlusion consists of some objects partially covering others. Those who cover up others perceive themselves as closer. It tells us that we are dealing with complete objects that are covered and not with fragments. Linear perspective refers to the effect of objects receding from the observer. The effect of convergence of parallels is what we have, for example, in a vineyard.
The vanishing point is the point where the parallel lines appear to converge. Aerial perspective is due to the dispersion of light produced by the atmosphere. Distant objects are perceived as diffuse and of a different color due to the atmosphere between the observer and the object. Shadows are not only those projected by the objects behind them, but also those from some parts of the object that are cast on others. This is very important in the perception of faces, it is a very powerful depth cue. It is usually interpreted as that there is a single source of light and that it comes from above; if we were below we would think that the light came from our heads.
This produces effects such as the writing tablet whose image appears different when rotated. Dynamics: Motion parallax is based on the change in perspective we have with respect to the object and of it with respect to others in the scene (absolute or relative). It is similar to stereopsis, but the different perspectives occur over time
Berkeley He alluded to the difficulty of perceiving the world in three dimensions, since we really see the world in two dimensions. Classically two approaches have been proposed:
- Yonatista: The perception of three-dimensionality is possible because the organism is ready for three-dimensional perception to occur.
- Empiricist: We are not genetically prepared, it is our experience with reality that allows this.
These two approaches agree that it works by cues, capturing retinal formation data to construct three-dimensionality.
Oculomotor: The information comes from muscle groups involved in vision. There are two groups: extraocular and ciliary. Information from these two groups is often redundant. Some of the movements are those whose objective is to focus the object on the retina, convergence movements in which the eyes converge on the place where the object is located.
For movement some muscles must contract and others retract. This can be a key away. When we look at an object of visual infinity the lens is flattened, the closer it is, the more bulging the lens will be. It would be a key associated with accommodation. But can there be three-dimensionality with just those two keys? The answer is yes, but from 6 meters the lens does not change, so from there it is not useful as a key. Therefore a system based only on these two keys would not be a very reliable system.