This first lecture introduces the organization of the visual system and the transmission of information. Image processing begins in the retina, with light absorption by photoreceptors, and transmission to the inner part of the retina, the optic nerve and the brain. There are two types of photoreceptor: rods, which account for the majority of photoreceptors (around 130 million in the human retina), and cones (around 5 million). Rods are distributed around the periphery of the retina, while cones are found mainly in the central region. There are no photoreceptors in the area of the optic nerve, which corresponds to the blind spot. The organization of the visual system includes a nocturnal and a diurnal system. In the nocturnal system, the rods operate from photon detection to starlight and beyond. They provide scotopic vision (vision in the dark), uncolored, with a gray scale. Cone vision is very precise diurnal (photopic) vision, enabling us to see from very little light (moonlight) to a maximum, to be avoided: sunlight. Color vision is also provided by cones. Between the nocturnal and diurnal systems, there is mesopic vision. The cones and rods constantly adjust the system to the intensity of light in real time, to the millisecond. The retina is the starting point for highly complex visual information processing: photoreceptor pigments capture light and transform it into an electrical signal. The image focused on the retina is conducted to bipolar and horizontal cells, then ganglion cells and the brain to the visual cortex, where processing of functions such as light signal intensity, color, contrast, etc. begins.
The lecture also discusses the neural substrate of the retina, the plasticity and adaptation of the visual system, the system's ability to adapt to highly variable light, and the connections with other senses such as hearing and touch, which enable complex processing of visual information. Color vision, color contrast and light intensity, as well as certain visual illusions, are also covered.
Our vision is a vision for action, encompassing highly complex processing, analytical mechanisms, dynamic processes, movement exploration, reconfiguration and plasticity of the system on an ongoing basis, involving conscious, non-conscious and constructed mechanisms over time.
