Sensation Outline Chapter 5, Psychology, David G Meyers, 7 th Edition Sensation the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment Perception the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events Sensation and Perception blend into one continuous process Bottom-Up Processing sensory analysis that starts at the entry level Top-Down Processing higher level analysis; construct perception by drawing on our experiences and expectations Failure of perception can take place anywhere between sensory detection and perceptual interpretation o Prosopagnosia condition involving complete sensation but incomplete perception. Loss of temporal lobe We only detect a small amount of the senses in the world Psychophysics study of relationships between the physical characteristics of stimuli, such as their intensity and our psychological experience of them Absolute Threshold The minimum stimulation necessary to detect a particular stimulus; Measured by recording the stimulation required for us to detect 50% of the time. Signal Detection Theory a theory predicting how and when we detect the presence of a faint stimulus [signal] amid background stimulation [noise] Assumes that there is no single absolute threshold and that detection depends partly on a persons experience, expectations, motivation, and level of fatigue Responsiveness increases when life or death on on the line (war situation) Peoples responsiveness decrease after 30 minutes of judging when a faint signal occurs Subliminal below ones absolute threshold for conscious awareness Yes, subliminal stimulus affects us Many experiments test by flashing positive or negative images before the group would respond to a stimuli; correlation between the subliminal and their reaction Although we can be affected by subliminal sensation, we cannot be influenced, or manipulated by hidden persuasion advertising. CBC study flashing message telephone now 352 times had no positive marketing affect. Difference Threshold or Just Noticeable Difference [JND] The minimum difference between two stimuli required for detection 50% of the time. We experience the difference threshold as a just noticeable difference Increases with magnitude of the stimulus
Weber s Law The principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount) o Light = 8% o Weight = 2% o Frequency = 0.3% Rough approximation, works well for non-extreme sensory stimuli Sensory Adaption our diminished/diminishing sensitivity to an unchanging stimulus Our eyes are constantly moving, quivering to maintain retinal stimulation Reduces our sensitivity, enables us to focus on informative changes in our environment o Frees our attention for more important things - Vision - Transduction conversion of one form of energy into another In sensation: the transforming of stimulus energies into neural impulses What we experience as color is really pulses of electromagnetic energy [Small part of electromagnetic radiation] Wavelength the distance from one wave peak to the next Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission Wavelength determines a lights hue Hue The color we experience from a light Intensity The amount of energy in a light or sound wave We perceive as brightness or loudness Determined by waves amplitude (height) Light enters the eye through the cornea Cornea protects the eye and bends light to provide focus Light passes through the pupil Pupil small adjustable opening through which light enters Iris muscle that controls the size of the pupil, this how much light is let in Ring of muscle that forms the colored portion of the eye Dilates and constricts in response to light intensity and inner emotions Subtly dilates to signal sexual interest Lens the transparent structure behind the pupil that changes shape to help focus the image on the retina Accommodation the process by which the eye s lens changes shape to focus near or far objects on the retina. Changes curvature Retina The light sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information Multilayered tissue Gets an inverted picture of what we see
Light image broken down into neural impulses, brain processes info and changes to upright orientation at the optical chasm Acuity the sharpness of vision; can be affected by small distortions in shape of eye Nearsightedness misshapen eyeball focuses light rays from distant objects in the front of the retina. Nearby objects are seen more clearly than distant objects Farsightedness faraway objects are seem more clearly than near objects Image focused behind the retina - The Retina - Light goes through outer cells before it reaches buried receptor cells, rods and cones Triggers chemical changes that generate neural signals Signals activate bipolar cells, which activate ganglion cells Rods retinal receptors that detect black, white, and gray Necessary for peripheral and twilight vision times when cones don t respond Cones receptor cells concentrated near the center of the retina Function in daylight and well-lit conditions Detect fine detail and color sensations Axons from ganglion cells from the Optic Nerve Optic Nerve nerve that carries neural impulses from the eye to the brain Blind Spot the point at which the optic nerve leaves the eye, creating a blind spot because no receptor cells are located there. Fovea the central focal point in the retina, around which the eye s cones cluster Cones have their own bipolar cell, relaying their precise info to the brain Processed in the occipital lobe the visual cortex at the back of the brain Feature Detectors nerve cells in the brain that respond to specific features of the stimulus such as shape, angle, or movement. Facial recognition comes from the temporal lobe Parallel Processing processing of several aspects of a problem simultaneously The brains natural mode of information processing for many functions Contrasts with step-by-step (serial) processing Damage to a portion of the visual cortex resulting in blindness in part of the field of vision is called blindsight - Color - Things appear a color because they reject the wavelength of the color they appear Wavelength determines color
Young Helmholtz Trichromatic (three-color) Theory Retina contains 3 different color receptors; for red, blue, and green When stimulated in combination can produce perception of any color Subtractive Color Mixing subtracts wavelengths from the reflected light o Mixed colors result in no wavelength left (brown/black) Additive Color Mixing adds wavelength, thus increasing light. Combining red, blue, and green equals white light Color blind people lack functioning cones Hering discovered afterimages Opponent-Process Theory the theory that opposing retinal processes enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green On Yellow Red Black Off Blue Green White If you detect one color you cannot detect the other Color Constancy perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object We see color because of our brains computations of the light reflected by any object relative to its surrounding objects. - Hearing - Audition the sense of hearing Hear frequencies that correspond to the range of the human voice Brief changes in air pressure transform into neural impulses that our brain interprets as sound Frequency The number of complete wavelengths that pass a point in a given time Pitch a tone s highness or lowness Depends on frequency Sound energy measured in decibels Absolute threshold 0 decibels Prolonged exposure to above 85 decibels speeds up hearing loss - The Ear -
Outer ear channels the sound waves through the auditory canal to the eardrum (tight membrane that vibrates) Middle Ear the chamber between the ear drum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrates the vibrations of the eardrum on the cochlea s oval window Inner Ear Snail shaped innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs. Cochlea a coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses. Cochlea s membrane called oval window Motion of vibrating oval window causes ripples in the basilar membrane, which is lined with hair cells Hair cells send neural messages to the temporal lobes auditory cortex Damage to hair cells causes most hearing loss cases Brain interprets loudness from number of hair cells triggered Hard of hearing people still hear loud sounds, only need soft sounds amplified [compressed] Perception of pitch comes from 2 theories Place Theory the theory that links the pitch we hear with the place where the cochlea s membrane is stimulated Hermann Von Helmholtz Explains high pitched sounds, not low pitched [neural signals not neatly located on Basilar membrane] Frequency Theory the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone Explain low range, but neural impulses cannot fire faster than 1000 times per second, ruling out upper third of piano Volley Principle group of neurons alternating firing, achieving greater than 1000 per second Place = High Pitches Frequency = Low Pitches Combination = Middle Pitches We locate sound by the slight timing differences between our two ears Stereophonic = Three Dimensional Brain uses parallel processing to locate sound - Hearing Loss / Deaf Culture Conduction Hearing Loss caused by damage to the mechanical system that conducts sound waves to the cochlea Ex. Eardrum punctured or tiny bones of middle ear stop vibrating Sensorineural Hearing Loss (AKA Nerve Deafness)
o Caused by damage to the cochlea s receptor cells [hair cells] or to the auditory nerves o Occasionally caused by disease, often biological changes with aging or loud noises o Once destroyed, remain dead. Cochlear Implant is an electronic device that translates sound into electrical signals that are wired into nerves. Implants are a debated issue because Deaf Culture argues that deafness is not a disability Sign is a real language with grammar and syntax When the brain is deprived of one sense, it enhances the others Those not involved in deaf culture/not sign fluent will feel more disabled and opt for implants - The Other Senses Touch is essential to our development Touch is a mix of pressure, warmth, cold, and pain Special nerve endings within skin create different reactions depending on where you are touched. No specific spots with specific feelings Only pressure has identifiable receptors The brain is wise enough to be most sensitive to unexpected stimulation Pain is a signal that something is wrong Pain is a property of: the senses, the region where we feel it, and the brain Phantom Limb Sensations brain can misinterpret the spontaneous central nervous system activity that occurs in the absence of normal sensory input Tinnitus The sound of silence ringing in the ears No brain, no pain. No one stimulus or receptor for pain. Integrated into other senses/receptors Gate-Control Theory theory that the spinal cord contains a neurological gate that blocks pain signals or allows them to pass on to the brain. The gate is opened by the activity of pain signals traveling up small nerve fibers and closed by activity in larger fibers or by information coming from the brain Can be altered by signals from the brain Pain can be totally stimulated by the brain, no sensory input You remember the most painful moments of pain; tapering down at the end reduces overall memory of pain Pain can be treated physically and psychologically by diverting attention away from pain
Taste is a mix of sweet, sour, salty, and bitter Taste is a chemical sense Umami savory- associated with monosodium glutamate [MSG] Taste buds reproduce themselves every week or two Smell adds to, and changes our perception of taste Sensory Interaction The principle that one sense may influence another, as when the smell of food influences its taste. McGurk Effect see a speaker say one syllable, while hearing another, out brain blends both creating a third syllable. The senses interact Smell = olfaction Smell is a chemical sense Olfactory receptors recognize odors individually Some odors come from combination Odors can evoke memories and emotion Smell is primitive - Body Position and Movement We have millions of position and motion sensors constantly sending information to the brain Kinesthesis the system for sensing the position and movement of individual body party Vestibular Sense the sense of body movement and position, including the sense of balance Biological gyroscopes for sense of equilibrium are in the inner ear Semicircular canals and vestibular sacs move when the head rotates or tilts, stimulating hair-like receptors, alerting the brain of body position and balance.