Sensing the world: some Basic Principles.
Sensation is the process where our sensory receptors and nervous system receive and represent stimulus energies from our environment.Perception is the process by which we organize and interpret this information. these processes are of one continuous process. Bottom-up processing is sensory analysis that begins at the entry level, with information flowing from the sensory receptors to the brain and Top -down processing is analysis that begins with the brain and flows down, filtering information through our experience and expectations to produce perception.
Each species comes with equipped with sensitive that enable it to survive and thrive. Psychophysics is the study of the relation between the physical characteristics of stimuli and our psychological experience of them. Our absolute threshold for any stimulus is the minimum stimulation necessary for us to be consciously aware of it 50 percent of the time. Signal detection theory demonstrates that individual absolute thresholds vary, depending on the strength of the signal and also on our experience. expectations, motivation, and alertness. Our difference threshold (also called just noticeable difference, or jnd) is the barely noticeable difference we discern between two stimuli 50 % of the time . As Weber's Law states to be perceptibly different, two stimuli must differ by a constant proportion ( such as 2% difference in weight), not a constant amount, if the original stimulus.
The priming effect and other experiments reveal that we can process some information from the stimuli below out absolute threshold for conscious awareness. But the restricted conditions under which it occurs would not enable unscrupulous opportunities to exploit us with subliminal messages.
Sensory adaption is our diminished sensitivity to constant or routine odors, sounds, and touches. We benefit from this phenomenon because it focuses our attention on informative changes in stimulation, rather than out unchanging elements in our environment.
Vision
Transduction is the process by which our sensory system encode stimulus energy as neural messages the brain can interpret. In vision, we convert light energy into these neural impulses. The energies we experience we experience as visible light are a thin slice from the broad spectrum of electromagnetic radiation. The hue and brightness we perceive in a light depend on the wavelength and intensity.
Light enters the eye through the cornea, a protective covering that bends the light ray. The Iris , a ring of muscle controls the size of the pupil, through which light enters. the lens changes shape to focus light rays on the retina, the inner surface of the eye, where receptors cells convert the light energy into neural impulses. After coding in the retina, the impulse travels along the optic nerve to the brain constructs the impulse it receives into an upright-seeming image. Distortions in the eye's shape can affect the sharpness of vision.The two types of receptors in the retina are the rods and the cones, and they differ in their shape, number, function, location, and the links to the brain. When the light enters the eye, it triggers a photochemical reaction in the rods and cone, which in turn activates bipolar cells, The bipolar cells activate ganglion cells and their axons (combined to from the optic nerve) transmit information (via the thalamus) to the visual cortex in the brain's occipital region. The more numerous rods, located mainly around the periphery of the retina, are more sensitive to light. Multiple rods send combined messages to a bipolar cell, and this pool of information lets us see rough images in dim light. Cones, concentrated in the fovea (at the center of t he retina), are sensitive to color and detail. A cone may link directly to a single bipolar cell, and this direct line to the brain preserves fine details in the cone's message.
Perception arise from the interaction of many neuron systems, each performing a simple task. Processing begins in the retina's multiple neural layers, and then the retina's 6 million cones and 120 million rods relay their information via bipolar cells to ganglion cells. Impulses travel along the ganglion cells' axons, which form the optic nerve, to the thalamus, and on to the visual cortex. In the visual cortex, feature detectors respond to specific features of the visual stimulus. Higher-levelsupercells areas. As sensory input passes through multiple levels of processing, it is influenced by our assumption, interests, and expectations.
Parallel processing is the brain's natural mode of information processing, in which it handles many aspects of a problem simultaneously. This multitasking ability lets the Brain distribute subdimensions of vision (color, movement, depth, and form) to separate neural teams that work separately and simultaneously. Other neural teams collaborate in integrating the results, comparing them with stored information, and enabling perception.
The Young-Helmholtz trichromatic (three-color) theory proposed that the retina contains three types of color receptors. Contemporary research has found three types of cones, each most sensitive to the wavelengths of one of the three primary colors of light (red,green, or blue). Hering's opponent-process theory proposed two additional color processes (red-versus-green and blue-versus-yellow) plus a third black-versus-white process. Contemporary research has confirmed that, en route to the brain, neurons in the retina and the thalamus code the color-related information from the cones into pairs of opponent colors, as demonstrated by afterimages. These two theories, and the research supporting them, show that color processing occurs in two stages. Color constancy is our ability to perceive consistent color on objects, even though the lighting and wavelength shift. this phenomenon demonstrates that our brain construct our experience of the color of an object through comparisons with other surrounding objects.
Hearing
Sound waves are bands of compressing and expanded air. our ears detect these changes in air pressure and transform them into neural impulses, which the brain decodes as sound. Sound waves vary in frequency and amplitude, which we perceive as differences in pitch and loudness.
The outer ear is visible portion of the ear. The middle ear is the chamber between the eardrum and cochlea. The inner ear consists of the cochlea, semicircular canals, and vestibular sacs. Through a mechanical chain of events, sound waves travelling through the auditory canal cause minuscule vibrations in the eardrum. The bones of the middle ear amplify the vibrations and relay them to the fluid-filled cochlea. Rippling of the basilar membrane, caused by pressure change in the cochlear fluid, causes movement of the tiny hair cells, triggering neural messages to be sent (via the thalamus) to the auditory cortex in the brain.Place theory proposes that our brain interprets a particular pitch by decoding the location (thus, "place") where a sound wave has stimulated the cochlea's basilar membrane. Frequency theory proposes that the brain deciphers the number and rate (thus "frequency") of the pulses traveling up the auditory nerve to the brain. research supports both theories, but for different ranges. Place theory cannot explain how we hear low-pitched sounds(which cannot be localized on the basilar membrane), but it can explain how we hear-pitched sounds (individual neurons cannot fire fast enough to produce the necessary number of surges), but it can explain our sensation of low-pitched sounds. some combination of the two explains how we hear in the middle range.
Sound waves strike one ear sooner and more intensely than the other. using parallel processing, the brain analyses the minute differences in the sounds received by the two ears and computes the source of the sound.
Conduction hearing loss results from damage to the mechanical system that transmit sound waves to the cochlea. Sensorineural hearing loss (or nerve deafness) results from damage to the cochlea's hair cells or their associated nerves. Diseases and accidents can cause these problems, but age-related disorders and prolonged exposure to loud noise are more common cause of hearing loss, especially of nerve deafness.
Cochlear implants are wired into various sites on the auditory nerve, allowing them to transmit electrical impulses to the brain. These devices can help deaf children to hear some sounds and to learn to use spoken language. But cochlear implants are most effective when children are very young, which means that parents must make this decision for their deaf children. Deaf culture advocates believe the operation is unnecessary since they do not see deafness as a disability- Deaf people already have a complete language, sign. Some further argue that sensory compensation, which enhances other senses, gives deaf people advantages that the hearing do not have.
Other Important Senses
Our sense of tough is actually four senses - pressure, warmth, cold, and pain-that combine to produce other sensations, such as "hot". Of these, only pressure has specialized receptors.
Pain is an alarm system that draws out attention to some physical problem. One theory of pain is that a "gate" in the spinal cord either opens to permit pain signals travelling up small nerve fibers to reach the brain, or closes to prevent their passage. The biopsychosocial perspective views a person's experience of pain as the sum of three sets of forces: biological influences, such as nerve fibers sending messages to the brain; psychological influences, such as the situation and out past experience; and social-cultural influences, such as cultural expectations and the presence of observers. Treatment to control pain often combine physiological elements.
Taste, a chemical sense, is a composite of five basic sensations - sweet, sour, salty, bitter, and unami- and of the aromas that interact with information from the taste buds. Taste buds on the top and sides of the tongue and in the back and on the roof of the mouth contain taste recipe cells. These cells send information to an area of the temporal lobe near the area where olfactory information is received. The influence of smell on our sense of taste is n example of sensory interaction, the ability of one sense to influence another.
Smell is a chemical sense too, but there are no basic sensations for smell. Unlike retina's receptor cells that sense color by breaking it into component parts, the 5 million olfactory receptor cells, with their approximately 350 different receptor proteins, recognize individual odor molecules. the receptor cells send messages to the brain's olfactory bulb, then to the temporal lobe and to parts of the limbic system. some odors trigger a combination of receptors. An odor's ability to spontaneously evoke memories and feelings is due in that part to the close connections between brain areas that process smell and those involved in memory storage.
Perception
Selective attention
In a process traditionally known as sensation, our senses of vision, hearing, taste, smell, and touch detect physical energy from the environment and encode it as neural signals. Aided by knowledge and expectations, or brain perceives meaning in these signals. We selectively attend to, and process, a limited number of the data bombarding our senses and block out the others. This focused attention can result in inattentional or change blindness, and even choice blindness.
Perceptual Illusion
Perceptual illusions fascinate psychologists because they reveal how we normally organize and interpret sensations. When visual and other sensory information conflict, our brain usually resolves the disagreement by accepting the visual data, a tendency known as visual capture. In contests between hearing and touch, hearing may dominate.
Perceptual Organization
Gestalt psychology searched for rules by which the brain organizes fragments of sensory data into gestalts (from the German word for “whole”), or meaningful forms. In pointing out that the whole is more than the sum of its parts, these researchers showed that we constantly filter sensory information and infer perception in ways that make sense to us. This truth remains valid, even though contemporary research demonstrates that sensation and perception are parts of a continuous information precessing system, involving both bottom-up and top-down processing.
To recognize an object, we must first perceive it (see it as a figure) as distinct from its surroundings (the ground). We bring order and form to stimuli by organizing them into meaningful groups, following the rules of proximity, similarity, continuity, connectedness, and closure.
Depth perception is out ability to see objects in three dimensions, even though our retinas receive two-dimensional images. Without depth perception, we would be unable to judge distance, height. Or depth. The visual cliff research with 6- to 14-months-old demonstrated that depth perception is in part innate. Many species perceive the world in three dimensions at, or very soon after, birth.
Binocular cues are depth cues that rely on information from both eyes. In the retinal disparity cue, the brain computes the relative distance of an object casts on our two retinas, the greater the difference, the closer the object must be. In the converge cue, the brain calculates the degree of neuromuscular strain when our two eyes turn inward to look at a nearby object. The greater the strain (or the angle of convergence), the closer the object.
Monocular cues let us judge depth using information transmitted by only one eye; binocular cues require information from both eyes. Monocular cues include.
● Relative size (smaller is more distant)
● interposition (an object that blocks another is closer than the blocked object)
● relative clarity (a hazy object is farther away than an object seen clearly)
● texture gradient (when texture changes, coarse distinct objects are closer and fine indistinct objects are distant).
● Relative motion or motion parallax (when you are moving objects closer than the fixation point appear to move backward – the nearer the object, the faster it moves; object beyond the fixation point appear to move with you).
● Linear perspective (the more two parallel lines converge, the farther away they are).
● Light and shadow (nearby objects reflect more light than faraway objects).
As objects move across or toward our retinas, our basic assumption is that shrinking objects are retreating, and enlarging objects are approaching. But our perception of motion is not always trustworthy. We may miscalculate the speed of movement of large objects or objects picked up by our peripheral vision. A quick succession of images on the retina can create an illusion of movement, as in stroboscopic movement (triggered by a rapid on-off blinking of two adjacent stationary lights).
Perceptual constancy is necessary in vision to recognize an object, regardless of its changing angle, distance, or illumination. Because of this ability, we perceive objects as having unchanging characteristics despite the changing images they cast on our retinas.
Shape constancy is our ability to perceive familiar objects (such as an opening door) as unchaining in shape, and size constancy is perceiving objects as unchanging in size, despite the changing images they cast on our retinas. There is a close relationship between perceived size and perceived distance. Knowing an object's size gives us clues about its size. This interplay sometimes misleads us, as when we misread monocular distance cues and reach the wrong conclusions, as in the Moon, Ponzo, and Mueller-Lyer illusions.
Lightness (or brightness) constancy is our ability to perceive an object as having a constant lightness even when its illumination – the light cast upon it – changes. Color constancy enables us to perceive the color of an object us unchanging even when its illumination changes. In both cases, the brain perceive the quality (lightness or color) relative to surrounding objects.
Perceptual Interpretation
If all aspects of visual perception were entirely inborn, people who were born blind but regained sight after surgery should have normal visual perception. They do not. After caratact surgery, for example, adults who had been blind from birth are able to distinguish figure from ground and to perceive colors, but they lack the experience to recognize shapes, forms, and complete faces. Further evidence comes from animals reared with severely restricted visual input, who suffered enduring visual handicaps when their exposure was returned to normal. Clinical and experimental evidence indicates that there is a critical period for some aspects of sensory and perceptual development. Without the stimulation provided by early visual experiences, the brain's neural organization does not develop normally.
When people are given glasses that shift the world slightly to the left or right, or even turn it upside down, they are initially disoriented, but they manage to adapt to their new context and, with practice, to move about it with ease. This research demonstrates our ability to adjust to an artificially altered visual field and coordinate our movements in response to that new world.
Perceptual set is a mental predisposition that functions as a lens through which we perceive the world. Once again, nature and nurture interact: Our sensory input bounces off our experiences, learned assumptions, and beliefs. Because our leaned concepts (schemas) prime us to organize and interpret ambiguous stimuli in certain ways, our perceptions reflect our vision of reality. Thus, some of us “see” monsters, faces, and UFOs or “hear” messages that other don't.
In perceiving a given stimulus that we could interpret by means of several different schemas, we scan the immediate context for information. Context creates expectations that guide our perceptions. Emotional context can color our interpretation of other people's behaviors - -and our own. Perceptual set and context effects interact to help us construct our perceptions.
Human factor psychologists encourage develops and designers to consider human perceptual abilities, to avoid the curse of knowledge (the mistaken assumptions that others share our expertise and will behave as we would), and to schedule user-testing to reveal perceptions-based problems before production and distribution. Human factors psychologists have contributed to improve safety in air and space travel; better-designed appliances, equipment, and workplaces; and easier-to-use assistive listening.
Is there Extrasensory Perception?
ESP (extrasensory perception) is one form of purported paranormal phenomena. (Another form is psychokinesis [PK].) The three most testable forms of ESP are telepathy (mind-to-mind communication), clairvoyance (perceiving remote events), and precognition (perceiving future events). Most research psychologists' skepticism focuses on two points. First, to believe is ESP, you must believe the brain is capable of perceiving without sensory input. Second (and most important in terms of critical inquiry), parapsychologists have been unable to replicate (reproduce) ESP phenomena under controlled conditions.
No comments:
Post a Comment