# Robot Bionic Vision Technologies: A Review
## 2 Literature Review
### Human Visual System
Visual information is further processed here, important visual information is extracted, useless information is discarded, and critical visual information is processed and transmitted to the primary “visual cortex” (3) V1 and then via V2 and V3 to V4, V5 (MT area), and higher brain areas [48; 49]. The visual flow is then processed layer by layer and transmitted to more areas on the surface of the brain, where the brain identifies the object in the eye’s view [50]. The “nerve tract” (4) runs through the brain and spinal cord throughout the body, and its main function is to control body movement [51]. motion, and position in the field of vision. The image information is then projected onto the ventral stream, also known as the \"what\" pathway, and the dorsal stream, also known as the \"where \" pathway, which is responsible for object recognition. The dorsal pathway is responsible for processing information such as movement and spatial orientation [55; 56; 57; 58]. The superior colliculus controls the unconscious eye and head movements, automatically aiming the eye at the target of interest in the field of vision and making it shoot into the fovea of the retina of the human eye. This area contains approximately 10 percent of the neurons in the human brain and is the primary area for visual projection in mammals and vertebrates. The anterior tectum controls iris activity to regulate pupil size [59]. As shown in Figure 2, light information first enters the Edinger-Westphal nucleus through the anterior tectum. The Edinger-Westphal nucleus has the following functions: (i) controlling the ciliary muscle to regulate the shape of the lens; (ii) controlling the ciliary ganglion; and (iii) regulating pupil size via cranial nerve III [60]. [PERSON] conducted anatomical experiments and studies on visual control in the rhesus-monkey brain. Stimuli and scans of the visual cortex of awake rhesus-monkey brains revealed that humans and nonhuman primates have similar visual control systems. However, the human brain is more complicated. Therefore, the similarity between the brain visual systems of rhesus monkeys and humans provides an important basis for humans to understand the principles of their eye movements and conduct experimental research [61; 62]. The visual cortex regions of the human and macaque brains are depicted in Figure 3.  
Figure 2: Human visual pathways. Copyright citation: This image is licensed by [PERSON]. Most mammals have two eyes that allow them to perform complex movements. Each eye is coordinated by six extraocular muscles according to [64]: the inner, outer, upper, and lower rectus muscles and the upper and lower oblique muscles. These muscles coordinate movements, allowing the eye to move freely in all directions and to change the line of sight as needed. The function of the internal and external rectus muscles is to turn the eyes inward and outward, respectively. Because the superior and inferior rectus muscles have an angle of 23\({}^{\circ}\) with the optic axis and the superior and inferior oblique muscles have an angle of 51\({}^{\circ}\) with the optic axis, they play a secondary role in addition to their main roles. The main function of the superior rectus muscle is upward rotation, whereas its secondary function is internal rotation. The main function of the inferior rectus muscle is downward rotation, and its secondary functions are internal and external rotation. The main function of the superior oblique is internal rotation, and the secondary functions are external and downward rotation. The main function of the inferior oblique is external rotation, and the secondary functions are external and upward rotation. In addition, the movement of the extraocular muscles is restricted to prevent the eyes from going beyond the range of motion, and mutually restricted extraocular muscles are called antagonistic muscles. Synergistic muscles are cooperative in one direction and antagonistic in another.