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How does light transform into vivid images in our eyes? Uncover the mystery of visual processing!
Our eyes are like windows, allowing light to enter and be transformed into vivid images in the brain. Visual processing is a three-dimensional and complex process, covering multiple brain structures and higher-level cognitive processes. Through these processes, we not only see the world around us, but also understand and perceive the information it conveys.
Light energy first enters the eye through the cornea, then passes through the pupil and lens, and is finally focused on the retina.
When light reaches the eye, the first step is to pass through the cornea, a layer of transparent tissue that refracts light. The light then passes through the pupil and lens, where it is further bent to focus it precisely on the retina. The retina contains photoreceptors, or light-sensitive cells, which are mainly divided into two types: rod cells and cone cells. Rod cells effectively monitor weak light, while cones process bright light sources.
Rod cells are sensitive to dim light, while cone cells are better at converting bright light.
When light is detected by photoreceptors in the retina, these cells convert the light signal into electrical signals, which are then passed to bipolar cells, which trigger action potentials in retinal ganglion cells. These retinal ganglion cells converge at the optic disc to form the optic nerve. The optic nerves from both eyes intersect at the optic chiasm, mapping each eye's field of view to the opposite cerebral hemisphere, helping the brain integrate visual information. Next, the visual path formed by the optic nerve bifurcates into two main visual pathways, named the medial geniculate pathway and the lateral geniculate pathway. These pathways transmit visual information to the visual cortex of the occipital lobe for higher-level processing. deal with.
Top-down and bottom-up visual representation
Our visual system is organized in a hierarchical fashion, with each anatomical region having specialized functions in visual processing. Low-order visual processing focuses on distinguishing different contrasts in images, while higher-order visual processing involves cognitive processes that integrate information from multiple sources. Object processing, such as object recognition and localization, is an example of higher-order visual processing. Higher-order visual processing relies on top-down and bottom-up processes. Bottom-up processing means that the visual system uses incoming visual information to transmit unidirectionally from the retina to higher cortical areas. Top-down processing refers to processing visual information based on previous knowledge and context, changing the information delivered by neurons, and adjusting their response to stimuli. Nearly all areas of the visual pathway can be affected by top-down processing. Traditionally, visual processing was thought to follow a unidirectional forward system, but increasing evidence shows that the visual pathway can operate in both directions, with both forward and feedback mechanisms, and that information can be passed back and forth between different layers of the cortex. .
Higher-order visual processing disorder
If the brain is damaged, it may lead to deficits in higher-order visual processing, including visual object agnosia, face agnosia, landmark agnosia and other disorders. These problems are caused by damage to brain structures involving the ventral or dorsal visual pathways. caused.
Processing of face and place stimuli
Past models have linked specific areas of visual processing to their corresponding stimulus types. For example, the parahippocampal area (PPA) located in the posterior temporal lobe has significantly enhanced activation for scenes of buildings and places, while the fusiform area (FFA) ) mainly show strong responses to faces and face-like stimuli.
The parahippocampal region shows enhanced neural responses when viewing buildings and houses.
On the other hand, the reason why FFA shows higher neural activation when stimulated by faces is because it is responsible for identifying facial features, but research also shows that it is not limited to faces. FFA also showed greater activation for visual stimuli in specialized domains, such as birds or cars. Experts in related studies generated activation of the FFA when distinguishing these objects, demonstrating the flexibility and adaptability of the FFA.
The development of FFA and PPA in the brain
Some studies indicate that the development of FFA and PPA is related to specialization in specific visual tasks and to other visual processing modes in the brain. Specifically, FFA activation is located in areas that process immediate visual field, while PPA activation is located in areas that process peripheral visual field. This means that the FFA and PPA may have developed some specialized functions due to the visual tasks faced by these fields of view.
Because faces are typically processed in immediate visual field, the brain areas associated with them develop to some degree as areas of expertise in facial recognition. Likewise, buildings and places are often viewed from the periphery of the field of vision, so areas associated with peripheral vision processing focus on the visual features of these buildings and places. In this way, our brains have undergone exquisite specialization and adaptation in visual processing, allowing us to better understand various details of the world.
Faced with such a complex and ingenious visual processing system, can we be more aware of the past and future of the visual system in daily life?
