Question

The Role of Light Discuss light’s role in visual perception. Give an example. 500 words min

Answer 1

Visual perception is the ability to interpret the surrounding environment using light in the visible spectrum reflected by the objects in the environment. This is different from visual acuity which refers to how clearly a person sees (for example "20/20 vision"). A person can have problem with visual perceptual processing even if he/she has 20/20 vision.

The resulting perception is also known as visual perception, eyesight, sight, or vision . The various physiological components involved in vision are referred to collectively as the visual system, and are the focus of much research in linguistics, psychology, cognitive science, neuroscience, and molecular biology, collectively referred to as vision science.

The visual system in animals allows individuals to assimilate information from their surroundings. The act of seeing starts when the cornea and then the lens of the eye focuses light from its surroundings onto a light-sensitive membrane in the back of the eye, called the retina. The retina is actually part of the brain that is isolated to serve as a transducer for the conversion of light into neuronal signals. Based on feedback from the visual system, the lens of the eye adjusts its thickness to focus light on the photoreceptive cells of the retina, also known as the rods and cones, which detect the photons of light and respond by producing neural impulses. These signals are processed via complex feedforward and feedback processes by different parts of the brain, from the retina upstream to central ganglia in the brain.

Note that up until now much of the above paragraph could apply to octopuses, mollusks, worms, insects and things more primitive; anything with a more concentrated nervous system and better eyes than say a jellyfish. However, the following applies to mammals generally and birds (in modified form): The retina in these more complex animals sends fibers (the optic nerve) to the lateral geniculate nucleus, to the primary and secondary visual cortex of the brain. Signals from the retina can also travel directly from the retina to the superior colliculus.

The perception of objects and the totality of the visual scene is accomplished by the visual association cortex. The visual association cortex combines all sensory information perceived by the striate cortex which contains thousands of modules that are part of modular neural networks. The neurons in the striate cortex send axons to the extrastriate cortex, a region in the visual association cortex that surrounds the striate cortex.

The human visual system is generally believed to perceive visible light in the range of wavelengths between 370 and 730 nanometers (0.00000037 to 0.00000073 meters) of the electromagnetic spectrum. However, some research suggests that humans can perceive light in wavelengths down to 340 nano meters (UV-A), especially the young.a lighting system that enhances the visual cues in a rendered image for the perception of 3D volumetric objects. We divide the lighting effects into global and local effects, and deploy three types of directional lights: the key light and accessory lights (fill and detail lights). The key light provides both lighting effects and carries the visual cues for the perception of local and global shapes and depth. The cues for local shapes are conveyed by gradient; those for global shapes are carried by shadows; and those for depth are provided by shadows and translucent objects. Fill lights produce global effects to increase the perceptibility. Detail lights generate local effects to improve the cues for local shapes. Our method quantifies the perception and uses an exhaustive search to set the lights. It configures accessory lights with the consideration of preserving the global impression conveyed by the key light. It ensures the feeling of smooth light movements in animations. With simplification, it achieves interactive frame rates and produces results that are visually indistinguishable from results using the non simplified algorithm.

• Three problems of perception
  • What is it? Perceptual Organization
  • Where is it? Depth Perception
  • What is it doing? Motion Perception
• Perceptual Organization: What is it?
  • Gestalt Psychology - described principles by which we organize sensations into groups
  • "the whole is greater than the sum of its parts"
  • Principles of Perceptual Organization
    • Figure/ground
    • Proximity
    • Similarity
    • Continuity
    • Closure
    • Connectedness
• Depth Perception: Where is it?
  • Problem: 2D images fall on our eyes but we perceive a 3D world?
  • How: Monocular and binocular cues
  • Binocular Cues
    • retinal disparity: difference between the two images (e.g., sterograms)
    • convergence: degree to which the eyes face inward
    • are clues to relative distance of different objects
  • Monocular cues
    • when objects are very far away,binocular cues don't provide enough info
    • monocular cues require only one eye
    • also called pictorial cues
    • linear perspective - parallel lines appear to converge with distance
    • relative size - if 2 objects appear the same size, the object casting the smaller image on the retina is perceived to be further away
    • interposition - if one object partially blocks our view of another object, we perceive it as close
    • texture gradient - the farther away an object, the less distinctive its texture
    • relative clarity - we perceive hazy objects as farther away
    • relative height - objects closer to the horizoon appear farther away
    • relative brightness - nearby objects reflect more light to our eyes - so brighter objects are perceived as being closer
    • relative motion - in a moving vehicle, objects in front of the fixation point appear to move opposite the direction of travel. Objects behind the fixation point, appear to move in the direction of travel
  • Size-Distance relationship
    • we infer the size of an object based on its perceived distance and the object's retinal size
    • if 2 objects cast identical retinal sizes (e.g., same size same distance away), the object appearing further away is perceived as larger
    • Ponzo illusion (also called the railroad-track illusion) - top line is perceived as longer because it is perceived (unconsciously) to be farther away -- but yet it is casting same sized image on retina -- hence it must be bigger.
    • The Ames Room
    • Muller-Lyer illusion - may be due to our experiences with corners