In this article we will make a brief summary of visual perception and the visual process that, although we have already developed amployally in the chapters of Visual perception, it is time to refresh some concept that will be good for us to enter the cognitive vision processes.
What is the visual process
The human being is related to the world through the senses, they transfer information, sensations, which pass to the brain and through its cognitive functional structure processes that information, interprets it and converts it into perception. The first problem we have is that most sensory stimuli are ambiguous and can cause the interpretation to be incorrect or even wrong.
Perception consists in obtaining information about the environment and giving it meaning, a sense that depends on cognitive processes and previous basic knowledge.
La visual perception It is characterized by a processing that goes from the retina to the primary occipital cortical areas, from where it bifurcates into two main pathways, the dorsal, which is directed towards the parietal lobes, specializing in “where” the objects are located and, a second, ventral pathway, which is directed towards the lobes temporary and that is responsible for the recognition and identification of objects.
Top-down and bottom-top processing
The majority of structures involved in the visual system, have a reciprocal relationship in their connections, this explains that the operation is organized in the eye movements and mechanisms from top to bottom and from bottom to top. The bottom-up processes are guided by sensitive information from the physical environment, while the top-down processes are guided by central elements, such as our beliefs, knowledge, etc. In most cases both processes are combined.
The interpretation of the world around us is determined by the interaction of two fundamental facts, the biological structure of our brain and the experience that modifies these structures. Every time we look at something, a mental representation of that part of the external world is generated, a representation that accumulates in the memory centers and that will be nourished by new representations of that same part of the world, with different angles, points of view, emotional charges, etc. and will serve as a basis for the subsequent recognition of that or something similar. This is especially important in children, who are increasing their representational "album" as they explore the environment around them. In children it has an additional importance, referred to the critical period, period in which the perceptual path is developed, a key period of time, so that if we go over it, certain procedural functions can no longer be given, because they were not learned, they did not develop during this initial period. This process is related to what we know as competition for the neural representation.
The outside world penetrates through the sensory organs, in this case the sight, and what the eye detects, the first element of the optic pathway, are: points, edges, colors, shapes, movements and textures, that is, attributes that are not yet objects but that once combined can define the objects we see, are the elements with which perception is constructed.
Points and edges
The photoreceptors of the retina converge in the bipolar cells and you are in the ganglion cells, in their campOn-off receivers, basis of edge perception. When the light strikes the campor receiver, in its area on, stimulation occurs at that point in the campor visual. If the light falls in its off zone, the cell is inhibited and no light is perceived.
In most cases, these campThe receptors have a central round area on and a peripheral zone that surrounds the previous one, like a donut, which is theampor off. If the light strikes the entire campor receiver, on and off, the cell is almost not excited because aampor neutralizes the other. With this conceptual basis, the detection of edges is explained, the phenomenon of seeing the illuminated side brighter next to the edge and the darker side less adjacent to the edge darker, is a way of enhancing the edge, as shown in the figure and which is known as Mach bands, in honor of the physicist who described them for the first time in 1865.
How do we detect the edges
In a visual representation of a rectangle of light next to a dark rectangle the campos receptors of ganglion cells (large outer circles) with + 10 excitatory regions and -5 inhibitory regions. Interesting answers occur on the border between the two rectangles. The graph at the bottom of the figure records the response in the different regions of the presentation.
El visual system It is specially designed to detect edges, which is where there is information, discarding uniform central areas, where information is scarce, it is a way to save energy. The visual system discards information that is not useful to you.
The information that reaches the brain reaches the primary visual cortex, which is organized in hypercolumns, functional modules with an approximate surface of 1 x 2 mm and a thickness of 4 mm. All the cells in a hypercolumn will be activated by stimuli that are represented in a small part of the campor visual The cells of the next hypercolumn will respond to the input of the neighboring part of the visual space. In each hypercolumn there is a particular sensitivity to the orientation of the edges, thus each hypercolumn shoots according to an orientation at the edges of the stimulus and the adjacent hypercolumn does so at a slightly different inclination to the previous one, to the point of being able to detect changes of 1º.
Visual perception
La information that reaches the brain from the eyes It is partial, that is, it is fragmented, the problem that the brain has is to regroup all that information, it has to decide which edges, colors, etc., belong to each object. It seems that the brain follows the "principles of clustering" described by Gestalt psychologists, the effect of proximity, uniform connectivity, coalination, similarity, etc.
The principles of grouping are maintained even when only parts of the object can be seen, which explains the frequent mistakes produced by stimuli in real life. We see things that do not really exist, such as the many visual illusions described by the Gestalt. These phenomena tell us that the visual perceptual system tries to fill empty spaces, tries to reconstruct objects by means of general rules of grouping.
The perception of illusory lines is due to the stimulation of neighboring neurons that have been activated by the presence of the stimulus, these contiguous zones in which there is no stimulus, will be activated in the same way as if there were, due to the effect of neighbors who did receive it, reconstructing the missing information, as in the figure, we identified a horseman on horseback.
The problem gets a little more complicated when the brain tries to link information of different characteristics, such as lines and colors, forms or others. It seems that the answer lies in the subject's attentive capacity (Treisman 1996).
Visual process
The information that comes to us from the primary visual areas is not sufficient for the recognition of the objects. To recognize is to match representations of an organized sensitive input with representations stored in the memory, in order to react against those stimuli from the outside world.
Factors of the visual process
In the process of visual recognition, factors such as:
- Point of view dependence: where, despite changing the angle of view, even if the elements of the perceived object change, we still identify the same object.
- Variation of the copy: if we identify a chair, even if they put us in front of another type of chair, with different shapes and characteristics, we will continue to identify that new object as a chair. This is because we compare the information of that chair with the images of chairs that we have in our memory (coincidence with a template), with some important characteristic of the chairs (model of coincidence of characteristics), by the three-dimensional structure (models of configuration) or by one of its components (model of recognition by components), explained this last with the geones of Biederman, 1995). The geones are useful units to describe the objects because their properties do not vary according to the perspective.
What we know governs what we see
The information that comes from the senses must be mixed with what we already know. The information below-above is related to the top-down information, it is a bidirectional flow. The information above helps interpret the information below. This means that what we see is not a faithful reflection of the world, not so much because the stimuli that enter are not real but because the interpretation we make of them is done in relation to the context at all levels of representation and perceptual processing. The information that arrives must not be interpreted in a unified way, it adapts to the deductions of the information above, to the context, this explains examples such as seeing an elongated object at night and believing that it is a man who persecutes us or a monster or, what of our imagination, our beliefs, our previous experiences, that is, our context. The recognition of objects can be improved if it is seen in an expected context, thus we will find more easily a friend among a group of people if we know that they should be among them.
In the same way, we know that there are elements that can facilitate or improve the level of recognition, perhaps the most important is that which is related to care. It seems that the mechanisms related to attention, would have a guiding value or recognition facilitator, it is as if superior cortical structures, tertiary level, could predispose to other lower level structures, such as the occipital V1 and V2 visual areas. They would help visual processing in its initial cortical stages, facilitating the recognition process.
What we see
The vision is an active process, destined to action, that is why in the visual process, in the recognition of objects, we are interested in knowing what they are and where they are located in space, in order to be able to act with them.
These two questions are processed in two different ways, the ventral and the dorsal, respectively. The dorsal pathway goes from the V1 areas to the parietal lobes, while the ventral line goes from V1 to V4 and the inferior temporal cortex. The information processed by each route follows different patterns but, finally, they converge in higher areas that help us to understand the world that is presented to us. The two routes would send afferences to the middle and lateral prefrontal areas, and from here they would arrive again, establishing interrelated circuits.
