Sensation and Perception Objectives

State the basic assumption we make in our perceptions of motion, and explain how these perceptions can be deceiving

As objects move across or toward our retinas, our basix 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 or the phi phenomenon

Describe two binocular cues for perceiving depth, and explain how they help the brain to compute distance

Binocular are depth cues that rely on information from both eyes. In the retinal disparity cue, the brain computes the relative distance of an object by comparing the slightly different images the objects casts on our two retinas. The greater the difference, the closer the object must be. In the convergence 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, the closer the object

Distinguish between kinesthesis and the vestibular sense.

By means of millions of position and motion sensors all over our body, our kinesthetic sense monitors the position and movement of our individual body parts. Our vestibular sense relies on semicircular canals and vestibular sacs in the inner ear to sende our head's- and thus our who,e body's- position and movement, letting us maintain our balance.

Describe how cochlear implants function, and explain why Deaf culture advocates object to these devices.

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.

Explain the importance of color constancy.

Color constancy is our ability to perceive consistent color in objects, even though the lighting and wavelengths shift. This phenomenon demonstrates that our brains construct or experience of the color of an object through comparisons with other surrounding objects.

Contrast the two types of hearing loss, and describe some of their causes.

Conduction hearing loss resukts from damage to the mechanical system that transmits sound waves to the cochlea. Sensorineural hearing lodd (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 causes of hearing loss, especially of nerve deafness.

Explain the importance of depth perception, and discuss the contribution of visual cliff research to our understanding of this ability

Depth perception is our 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 olds demonstrated that depth perception is in part innate. Many species perceive the world in three dimensions at, or very soon after, birth

Identify the three most testable forms of ESP, and explain why most research psychologists remain skeptical of ESP claims

ESP is one form of purported paranormal phenomena. The three most testable forms of ESP are telepathy, clairvoyance, and precognition. Most research psychologists' skepticism focuses on two points. First, to believe in ESP, you must believe the brain is capable of perceiving without sensory input. Second, parapsychologists have been unable to replicated ESP phenomena under controlled conditions.

Distinguish between absolute and difference thresholds, and discuss whether we can sense stimuli below our absolute thresholds and be influenced by them.

Each species comes equipped with sensitivies that enable it to survive and thrive. Psychophysics is the study of the relationships 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% of the time. Signal detection theory demonstrated that individual thresholds vary, depending on the strength of the signal and also on our experience, expectations, motivation, and alertness. Our difference threshold (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, not a constant amount, of the original stimulus. The priming effect and other experiments reveal that we can process some information from stimuli below our absolute threshold for conscious awareness. But the restricted conditions under which it occurs would not enable unscrupuloud opportunities to exploit us with subliminal messages.

Describe Gestalt psychology's contribution to our understanding of perception

Gestalt psychologists searched for rules by which the brain organizes fragments of sensory data into gestalts, or meaningful forms. In pointing out that the whole is more than the sum of its parts, these researchers showed that we constantly filer sensory information and infer perceptions in way that make sense to us. This truth remains vald, even though contemporary research demonstrates that sensation and perception are parts of a continuous information processing system, involving both bottom-up and top-down processing

Describe the role human factors psychologists play in creating user-friendly machines and work settings

Human factors psychologists encourage developers and designers to consider human perceptual abilities, to avoid the curse of knowledge, and to schedule user-testing to reveal perception-based problems before production and distribution. Human factors psychologists have contributed to improved safety in air and space travel; better-designed appliances, equipment, and work-places; and easier-to-use assistive listening

Describe the contribution of restored-vision and sensory deprivation research in our understanding of the nature-nurture interplay in our percpetions

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 cataract 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 recognized shapes, forms, and complete faces. Further evidence comes from animals reared with severely restricted visual input, who suffered enduring visual handicaps when their visual exposure was returned to normal. Clinical and experimental evidence indicated 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.

Describe the interplay between attention and perception

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, our brain perceives meaning in these signals. We selectively attend to, and process, a limited number of the data bombarding our sense and block out the others. This focused attention can result in inattentional or change blindness, and even choice blindness.

Explain why the same stimulus can evoke different perceptions in different contexts

In perceiving a give stimulus that we could interpret by means of several different schemas, we scan the immediate context for information. Connect 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.

Describe the major structures of the eye, and explain how they guide an incoming ray of light toward the eye's receptor cells.

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 receptor cells convert the light energy into neural impulses. After coding in the retina, the impulses travel along the optic nerve to the brain. Although the retina receives and upside-down image, the brain constructs the impulses it receives into an upright-seeming image. Distortions in the eye's shape can affect the sharpness of vision.

Discuss lightness constancy and its similarity to color constancy

Lightness 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 as unchanging even when the illumination changes. In both cases, the brain perceives the quality relative to the surrounding objects

Explain how monocular cues differ from binocular cues, and describe several monocular cues for perceiving depth

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 interposition relative clarity texture gradient relative height relative motion or motion parallax, linear perspective light and shadow

Describe the sense of touch.

Our sense of touch 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.

State the purpose of pain, and describe the biopsychosocial perspective on pain.

Pain is an alarm system that draws our attention to some physical problem. One theory of pain is that a "gate" in the spinal cord either opens up to permit pain signals traveling up small nerve fibers to reach the brain, or closes to prevent their passage. The biopsychosocial perspectivr views a person's experience of pain as a sum of three sets of forces: biological influences, such as nerve fibers dending messages to the brain; psychological influences, such as the situation and our past experiences; and socio-cultural influences, such as cultural expectations and the presence of others. Treatments to control pain often combine physiological and psychological elements.

Define parallel processing, and discuss its role in visual information processing.

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 perceptions.

Discuss the different levels of processing of visual information traveling from the eye's retina to the brain's cortex.

Perceptions 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 cell's 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-level supercells integrate this pool of data for processing in other cortical areas. As sensory input passes through multiple levels of processing, it is influenced by our assumptions, interests, and expectations.

Explain the importance of percpetual constancy

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

Explain how illusions help us to understand some of the ways we organize stimuli into meaningful perceptions

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

Define perceptual set, and explain how it influences what we do or do not perceive

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 learned concepts prime us to organize and interpret ambiguous stimuli in certain ways, our perceptions reflect our version of reality. Thus, some of "see" monsters, faces, and UFOs or "hear" messages that others do not.

Contrast place and frequency theories, and explain how they help us to understand pitch perception.

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 our sensation of high-pitched sounds. Frequency theory cannot explain how we hear high-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 sounds in the middle range.

Contrast sensation and perception, and explain the difference between bottom-up and top-down processing.

Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from the environment. Perception is the process by which we organize and interpret this information. Although we view sensation and perception separately to analyze and discuss them, they are actually parts of one continuous process. Bottom-up processing is sensory analysis that begins at the entry level, with informstion flowing from the sensory receptors to the brain. Top-down processing is analysis that begins with the brain and flows down, filtering information through our experience and expectations to produce perceptions.

Describe sensory adaptation, and explain how we benefit from being unaware of unchanging stimuli.

Sensory adaptation is our diminished sensitivity to constant or routine odors, sounds, and touches. We benefit from tnis phenomenon because it focuses our attention on informative changes in stimulation, rather than on unchanging elements in our environment.

Describe the shape and size constancies, and explain how our expectations about perceived size and distance contribute to some visual illusions

Shape constancy is our ability to perceive familiar objects as unchanging 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 to its distance knowing its distance gives 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 Muller-Lyer illusions

Describe the sense of smell, and explain why specific odors so easily trigger memories.

Smell is a chemical sense, but there are no basic sensations forsmell, as there are for touch and taste. Unlike the 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 part to the close connections between brain areas that process smell and those involved in memory storage.

Describe the pressure waves we experience as sound.

Sound waves are bands of compressed 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.

Describe how we pinpoint sounds.

Sound waves strike one ear sooner and more intensely than the other. Using parallel processing, the brain analyzes the minute differences in the sounds received by the two ears and computes the source of the sound.

Describe the sense of taste, and explain the principle of sensory interaction.

Taste, a chemical sense, is a composite of five basic sensations- sweet, sour, salty, bitter, and umami- and the aromas that interact with infromation 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 receptor 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 an example of sensory interaction, the ability of one sense to influence another.

Explain how the Young-Helmholtz and opponent process theories help us understand color vision.

The Young-Helmholtz trichromatic 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.

Describe the three regions of the ear, and outline the series of events that triggers the electrical impulses sent to the brain.

The outer ear is the visible portion of the ear. The middle ear is the chamber between the eardrum and the cochlea. The inner ear consists of the cochlea, semicircular canals, and vestibular sacs. Through a mechanical chain of events, sound waves traveling through the auditory canal cause miniscule 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 changes in the cochlear fluid, causes movement of the tiny hair cells, triggering neural messages to be sent (via the thalamus) to the auditory cortex of the brain.

Contrast the two types of receptor cells in the retina, and describe the retina's reaction to light.

The two types of receptor cells in the retina are the rods and the cones, and they differ in their shape, number, function, location, and links to the brain. When light enters the eye, it triggers a photochemical reaction in the rods and cones, which in turn activates bipolar cells. The bipolar cells activate ganglion cells, and their axons (combined to form 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 the 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.

Explain the figure-ground relationship, and identify principles of perceptual grouping in form perception

To recognize an object, we must first perceive it as distinct from its surrounding. We bring order and form to stimuli by organizing them into meaningful groups, following the rules of proximity, similarity, continuity, connectedness, and closure.

Define transduction, and specify the form of energy our visual system converts into the neural messages our brain can interpret.

Transduction is the process by which our sensory systems encode stimulus energy as neural messages the brain can interpret. In vision, we convert light energy into these neural impulses. The energies 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.

Explain how the research on distorting goggles increases our understanding of the adaptability of perception

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 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.