Visual perception - Wikipedia
The physical stimulus present in the environment emits energy that is The line of difference between sensation and perception is now drawn; For instance, seeing the light (sensation) is different from determining its color (perception). Define sensation and explain its connection to the concepts of absolute Absolute threshold refers to the minimum amount of stimulus energy that must be present .. vision during critical periods of development have trouble perceiving depth. Visual perception is the ability to interpret the surrounding environment using light in the visible The act of seeing starts when the cornea and then the lens of the eye focuses light from its surroundings onto a The visual association cortex combines all sensory information perceived by the striate cortex which contains.
Sensation and Perception
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 octopusesmolluskswormsinsects 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 nucleusto 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 cortexa region in the visual association cortex that surrounds the striate cortex. Two-streams hypothesis The major problem in visual perception is that what people see is not simply a translation of retinal stimuli i. Thus people interested in perception have long struggled to explain what visual processing does to create what is actually seen.
Early studies[ edit ] The visual dorsal stream green and ventral stream purple are shown. Much of the human cerebral cortex is involved in vision. There were two major ancient Greek schools, providing a primitive explanation of how vision is carried out in the body.
The first was the " emission theory " which maintained that vision occurs when rays emanate from the eyes and are intercepted by visual objects. If an object was seen directly it was by 'means of rays' coming out of the eyes and again falling on the object. A refracted image was, however, seen by 'means of rays' as well, which came out of the eyes, traversed through the air, and after refraction, fell on the visible object which was sighted as the result of the movement of the rays from the eye.
This theory was championed by scholars like Euclid and Ptolemy and their followers. The second school advocated the so-called 'intro-mission' approach which sees vision as coming from something entering the eyes representative of the object. With its main propagators AristotleGalen and their followers, this theory seems to have some contact with modern theories of what vision really is, but it remained only a speculation lacking any experimental foundation. Plato makes this assertion in his dialogue Timaeusas does Aristotlein his De Sensu.
The eye has a central line and everything that reaches the eye through this central line can be seen distinctly. Alhazen — c. He wrote "The function of the human eye But I found it to be completely different.
Although he did not use these words literally he actually is the father of the modern distinction between foveal and peripheral vision. Unconscious inference Hermann von Helmholtz is often credited with the first study of visual perception in modern times.
Helmholtz examined the human eye and concluded that it was, optically, rather poor. The poor-quality information gathered via the eye seemed to him to make vision impossible. He therefore concluded that vision could only be the result of some form of unconscious inferences: Examples of well-known assumptions, based on visual experience, are: Another type of the unconscious inference hypothesis based on probabilities has recently been revived in so-called Bayesian studies of visual perception.
However, it is not clear how proponents of this view derive, in principle, the relevant probabilities required by the Bayesian equation.
Models based on this idea have been used to describe various visual perceptual functions, such as the perception of motionthe perception of depthand figure-ground perception. Gestalt psychology Gestalt psychologists working primarily in the s and s raised many of the research questions that are studied by vision scientists today . The Gestalt Laws of Organization have guided the study of how people perceive visual components as organized patterns or wholes, instead of many different parts.
According to this theory, there are eight main factors that determine how the visual system automatically groups elements into patterns: Analysis of eye movement[ edit ] See also: Eye movement Eye movement first 2 seconds YarbusDuring the s, technical development permitted the continuous registration of eye movement during reading  in picture viewing  and later in visual problem solving  and when headset-cameras became available, also during driving.
While the background is out of focus, representing the peripheral visionthe first eye movement goes to the boots of the man just because they are very near the starting fixation and have a reasonable contrast.
The following fixations jump from face to face. They might even permit comparisons between faces. The societal emphasis on understanding strictly through the rational side of our brain, which constitutes a small portion of our native intelligence, is misguided at best, arrogant at worst. We are not conscious beings, not yet. Our great potential is found in the search for consciousness, in the striving towards deeper forms of knowing.
Our minds and our senses are designed to be educated, to be used and developed—and this means much more than the rote gathering of facts, or the highly-distracted seeing of the world through the screen of the newest, lusted-after digital device.
Deep Perception: Cultivating the Art of Seeing
In losing an eye, I directly experienced the neuroplasticity of the brain and its remarkable ability—over a short six months—to forge new connections in the act of perception based on monocular vision, inner sensations, and sound. The yearning for vision of itself opens the door to new neural and cellular connections. We need to look far, look wide, look inward while looking outward, and to question and scrutinize, examine, seek out and take in all of those impressions that reach our senses from a large variety of sources.
We need to resist passive forms of perception and the quick judgments of formulaic thinking.
Difference between Looking and Seeing
What will it be for us now, and for the future? Growth, development and evolution, or passivity, entropy and the gradual withering of the great perceptual capacities that we now enjoy, that are distinctly human?
Poet Theodore Roethke writes: Are we awake to our capacity for sight and all that it implies? Do we know how to see. From birth to death, we use our eyes constantly and unceasingly. For the most part, this is an automatic activity. As we grow from childhood to adulthood, the process of socialization and the development of our personalities is based chiefly on the acquisition of knowledge and the development of our unique talents or worldly skills.
We learn the labels of things, how to read the world through vision, how to navigate through space and through our lives, but we do not fully address what happens at the point of intersection of receiving an impression. Moreover, this impression taken in through vision may be received only in part through our eyes. It may be an impression that is initiated through the eyes, and is realized through feeling, empathy, or intuitive insight.
Or, it may be an impression of ourselves in the midst of our lives — self-observation. The gift of observation, of the inner and outer worlds and their profound relationship, can be cultivated — indeed, must be — if we wish to live full and authentic lives, sensitively receiving and richly giving to ourselves and others.
To see implies conscious intent — the ability to direct our attention, to focus our gaze, and to concentrate our energies in a desired direction. We know and sense, from rumblings deep within and confirmed by our life experience, that this full, enveloping quality of concentration is the paradoxical heart of what brings us into a deeper relationship with ourselves and the world around us. It is paradoxical because this single-pointed concentration is like an hourglass; as we focus intensely on a single factor, something widens, opens, and deepens.
The world is revealed in a single shape, a single gesture.
Walt Whitman reminds us of this: I believe that a leaf of grass is no less than the journey-work of the stars, and the pismire is equally perfect, and a grain of sand.
We are called toward awareness by the conditions of our lives: From time to time, another voice is heard — the call from within, or the growing recognition of our lack of attention and real care, our lack of a full relationship with self and others, and our wish for this to be different — our wish to be.
What can we gain through cultivating awareness? If we could truly open the windows of perception, our lives would be infinitely richer, finer, truer to the possibilities of the soul.