Psychology Chapter 5: Sensation and Perception

Transcription

1 Psychlgy Chapter 5: Sensatin and Perceptin Sensatin: the stimulus-detectin prcess by which ur sense rgans respnd t and translate envirnmental stimuli int nerve impulses that are sent t the brain Perceptin: making sense f what ur senses tell us is the active prcess f rganizing this stimulus input and giving it meaning Sensry Prcesses: - Five classical senses: visin, auditin (hearing), tuch, gestatin (taste), and lfactin (smell) - Human sensry systems are designed t extract frm the envirnment the infrmatin that we need t functin and survive Psychphysics: studies relatins between the physical characteristics f stimuli and sensry capabilities - Cncerned with tw kinds f sensitivity: the abslute limits f sensitivity, and the differences between stimuli The Abslute Threshld fr Stimulus Detectin: Hw intense a stimulus must be befre we can detect its presence The Abslute Threshld: the lwest intensity at which a stimulus can be detected crrectly 50 percent f the time. The lwer the abslute threshld, the greater the sensitivity. Signal Detectin Thery: Cncerned with the factrs that influence sensry judgments - Decisin Criteria: a standard f hw certain a persn much be that a stimulus is present befre they will say they detect it - Can change depending n fatigue, expectatin, and the ptential significance f the stimulus. - Fur pssible utcmes in signal detectin: A hit: a tne is presented and the participant detects it A miss: a tne is presented and the participant des nt detect it A false alarm: n tne is presented and the participant detects it A crrect rejectin: n tne is presented and the participant des nt detect it The Difference Threshld: the smallest difference between tw stimuli that peple can perceive 50 percent f the time; smetimes called the just nticeable difference - Weber s law: the difference threshld is directly prprtinal t the magnitude f the stimulus with which the cmparisn id being made, and can be expressed as a Weber fractin - Example: the Weber fractin fr weights id 1/50. If yu lift a weight f 50 grams, anther weight must be 51 g t detect a difference; 500g t 510g etc. Sensry Adaptatin: the diminishing sensitivity t unchanging stimuli; due t adaptatin r habituatin The Sensry Systems: Visin: nrmal stimulus is electrmagnetic energy, r light waves; measures in nanmeters Our visual system is nly sensitive t wavelengths frm 700 nm (red) t 400 nm (blue-vilet) The Human Eye:

2 - Crnea: where light waves enter the eye, a transparent prtective structure at the frnt - Pupil: behind the crnea, an adjustable pening that can dilate r cnstrict t cntrl light entry - Iris: clred area arund pupil, cntains muscles that cntrl the pupil s size - Lens: behind the pupil, an elastic structure that becmes thinner r thicker t fcus - Retina: multi-layered tissue at the rear f the eyeball, where the lens fcuses the visual image The ability t see clearly depends n the lens s ability t fcus the image nt the retina Mypia (nearsightedness): The lens fcuses the visual image in frnt f the retina (t near the lens) resulting in a blurred image fr faraway bjects. This generally ccurs because the eyeball is lnger than nrmal Hyperpia (farsightedness): The lens des nt thicken enugh and the image is therefre fcused n a pint behind the retina (t far frm the lens). The aging prcess causes the eyeball t becme shrter ver time, causing hyperpia Phtreceptrs: - The retina cntains tw types f light-sensitive receptr cells, called rds and cnes - There are abut 120 millin rds and nly 6 millin cnes Rds: functin best in dim light, black and white brightness receptrs, 500 times mre sensitive t light than cnes, but d nt give rise t clur sensatin Cnes: clur receptrs, functin best in bright illuminatin Rds are fund thrughut the retina except in the fvea (a small area in the centre f the retina that cntains nly cnes) Cnes decrease in cncentratin as ne mves away frm the centre f the retina Rds and cnes synapse with a layer f biplar cells, which then synapse with a layer f ganglin cells t cmmunicate with the brain The axns f the ganglin cells are cllected int a bundle t frm the ptic nerve Visual Transductin: the prcess whereby the characteristics f a stimulus are cnverted int nerve impulses - Phtpigments: the prtein mlecules trugh which rds and cnes translate light waves int nerve impulses Brightness Visin and Dark Adaptatin: - Rds are far mre sensitive that cnes under lw illuminatin - Rds have much greater brightness sensitivity than cnes thrughut the clur spectrum except at the red end, where rds are relatively insensitive. - Cnes are mst sensitive t lw illuminatin in the greenish-yellw range f the spectrum Dark Adaptatin: the prgressive imprvement in brightness sensitivity that ccurs ver time under cnditins f lw illuminatin - Phtreceptrs becme depleted f their pigment mlecules fr a perid f time after absrbing light - In dark adaptatin, the phtpigment mlecules are regenerated and the receptr s sensitivity increases - Cnes regenerate faster than rds Clur Visin: tw different theries f clur visin

3 The Trichrmatic Thery: There are three types f clur receptrs in the retina - Althugh all cnes can be stimulated by mst wavelengths t sme degree, individual cnes are sensitive t wavelengths that crrespnd t blue, green, r red - Each f these receptr classes sends messages t the brain based n the extent t which they are activated - The visual system cmbines the signals t recreate the riginal hue Oppnent-Prcess Thery: Each f the three cne types respnds t tw different wavelengths. One type respnds t red r green, anther t blue r yellw, and a third t black r white Dual-Prcess Thery: Cmbines the trichrmatic and ppnent-prcess theries t accunt fr clur transductin Clur-Deficient Visin: - Trichrmats: peple with nrmal clur visin, sensitive t all 3 systems red-green, yellw-blue, black-white - Dichrmats: peple wh are clur-blind in nly ne f the systems (red-green r yellw-blue) - Mnchrmats: peple wh are sensitive nly t the black-white system and are ttally clur blind Analysis and Recnstructin f Visual Scenes: After light energy is transfrmed in t nerve impulses, the messages received frm the phtreceptrs are cmbined int the perceptin f a visual scene Feature Detectrs: grups f neurns within the primary visual crtex (in the ccipital lbe) that receive and integrate sensry nerve impulses riginating in specific regins f the retina; fire selectively in respnse t stimuli that have specific characteristics Parallel Prcessing: simultaneus analyzing f smething s clur, shape, distance, and mvement t cnstruct a unified image f its prperties Visual Assciatin Prcesses: infrmatin analyzed and recmbined by the primary visual crtex is ruted t the visual assciatin crtex where mre cmplex features f the visual scene are cmbined and interpreted Auditin: stimuli fr ur sense f hearing are sund waves, a frm f mechanical energy Sund is actually pressure waves in the air, water, r sme ther cnductin medium Frequency: the number f sund waves r cycles per secnd- - cycles per secnd are measured in hertz (Hz) - sund waves frequency is related t pitch higher frequency = higher pitch Amplitude: the vertical size f the sund waves - the amunt f cmpressin and expansin f the mlecules in the cnducting medium - the primary determinant f the sund s perceived ludness - expressed as decibels (db) Auditry Transductin: Transductin system made up f tiny bnes, membranes, and liquid-filled tubes designed t translate pressure waves int nerve impulses - sund waves travel in an auditry canal - leads t the eardrum: a mvable membrane that vibrates in respnse t the sund waves

4 - middle ear: a cavity husing three tiny bnes (the hammer, anvil, and stirrup) beynd the eardrum these bnes vibrate t amplify the sund waves mre than 30 times hammer attatched t the eardrum, stirrup- attatched t the val windw- a membrane that frms the bundary between the middle and inner ear - inner ear: cntains the cchlea cchlea: a ciled snail-shaped tube that is filled with fluid and cntains the basilar membrane basilar membrane: a sheet f tissue that runs the length f the cchlea rgan f Crti: rests n the basilar membrane, cntaining thusands f tiny hair cells the actual sund receptrs the hair cells synapse with the neurns f the auditry nerve that sends impulses via an auditry relay statin in the thalamus t the auditry crtex (in the tempral lbe) Sund waves strike the eardrum and create pressure at the val windw by the hammer, anvil, and stirrup, setting the fluid inside the cchlea int mtin. The fluid waves vibrate the basilar membrane and the membrane abve it, causing the hair cells in the rgan r Crti t bend. This bending triggers a release f neurtransmitter substance resulting in nerve impulses sent t the brain Cding f Pitch and Ludness: The auditry system transfrms the sensry qualities f ludness and pitch int the language f nerve impulses. High-Amplitude sund waves cause the hair cells t bend mre and release mre neurtransmitter substance luder Frequency Thery f Pitch Perceptin: nerve impulses sent t the brain match the frequency f the sund wave Place Thery f Pitch Perceptin: the specific pint in the cchlea where the fluid wave peaks and mst strngly bends the hair cells serves as a frequency cding cue Sund Lcalizatin: The nervus system uses infrmatin cncerning the time and intensity differences f sunds arriving at the tw ears t lcate the surce f sunds in space - sunds arrive first and ludest at the ear clsest t the sund; when the sund is in frnt r behind us, the sund wave reaches bth ears at the same time and at the same intensity Hearing Lss: Tw majr types Cnductin Deafness: caused by prblems invlving the mechanical system that transmits sund waves t the cchlea - can be caused by puncturing an eardrum r lss f functin in the tiny bnes Nerve Deafness: caused by damaged receptrs within the inner ear r damage t the auditry nerve itself - cannt be helped by a hearing aid - can be caused by aging and disease Taste and Smell: chemical senses because their receptrs are sensitive t chemical mlecules rather than energy Gustatin: sense f taste - sense f taste respnds nly t fur qualities: sweet, sur, salty, bitter - every ther taste experience cmbines these qualities and thse f ther senses, such as smell, temperature, and tuch

5 Taste Buds: chemical receptrs cncentrated alng the edges and back surface f the tngue - We have a small number f receptrs n the rf and back f the muth - Taste buds cnsist f several receptr cells - Hairlike structures prject frm the tp f each cell int the taste pre, an pening in the surface f the tngue - Substances taken int the muth interact with saliva t frm a chemical slutin that stimulates receptr cells - A taste results frm cmplex patterns f neural activity prduced by the fur types f taste receptrs Olfactin: sense f smell - Receptrs are lng cells that prject thrugh the lining f the upper part f the nasal cavity and int the mucus membrane - We have abut 40 millin lfactry receptrs - Mst ppular thery is that lfactry receptrs recgnize diverse drs individually rather than by mixing the activity f fewer basic receptrs like in taste - Receptrs have receptr structures that resemble neurtransmitter binding sites n neurns - Odr mlecules can lck int sites that are tailred t fit them Phermnes: chemical signals fund in natural bdy scents Menstrual Synchrny: the tendency f wmen wh live tgether r are clse friends t becme mre similar in their menstrual cycles The Skin and Bdy Senses: include senses f tuch, kinesthesis (muscle mvement), and equilibrium The Tactile Senses: we are sensitive t at least fur tactile sensatins: pressure (tuch), pain, warmth, and cld - These are cnveyed by receptrs in the skin and in ur internal rgans. - All ther cmmn skin sensatins are mixtures f thse fur sensatins Free Nerve Endings: the primary receptrs fr pain and temperature; simple nerve cells beneath the skin s surface The brain can lcate sensatins because skin receptrs send their messages t the pint in the smatsensry crtex that crrespnds t the area f the bdy where the receptr is lcated The Bdy Senses: kinesthesis and equilibrium Kinesthesis: prvides us with feedback abut ur muscles and jints psitins and mvements Receptrs are nerve ending in the muscles, tendns, and jints Gives us the basis fr making crdinated mvements Vestibular Sense: the sense f bdy rientatin r equilibrium; cperates with kinesthesis Receptrs are lcated in the vestibular apparatus f the inner ear One part f the equilibrium system cnsists f three semicircular canals: which cntain receptrs fr head mvement Vestibular sacs als cntain hair cells that respnd t the psitin f the bdy and tell us if we are upright r tilted at an angle Perceptin: an active creative prcess in which raw sensry data are rganized and given meaning

6 The brain has tw different kinds f prcessing functins t create ur perceptins Bttm-up Prcessing: the system takes in individual elements f the stimulus and then cmbines them int a unified perceptin Tp-dwn Prcessing: sensry infrmatin is interpreted in the light f existing knwledge, cncepts, ideas, and expectatins Attentin: invlves tw prcesses f selectin fcusing n certain stimuli and filtering ut ther incming infrmatin - Attentin is affected by bth the nature f the stimulus and by persnal factrs - Our attentin is attracted by intensity, nvelty, mvement, cntrast, and repetitin - Our mtives and interests act as pwerful filters fr what we fcus ur attentin n Gestalt Principles f Perceptual Organizatin: Believed in tp-dwn prcessing the whles we perceive are ften mre than the sum f their parts Figure-grund relatins: we tend t rganize stimuli int a central r fregrund figure and a backgrund; the central figure is mre striking in ur perceptins and memry Gestalt laws f perceptual rganizatin: similarity, prximity, clsure, cntinuity; hw we grup and interpret stimuli - Law f similarity: when parts f a cnfiguratin are perceived as similar, they will be perceives as belnging tgether - Law f prximity: elements that are near ne anther are likely t be perceived as part f the same cnfiguratin - Law f clsure: peple tent t clse the pen edges f a figure r fill in gaps in an incmplete figure - Law f cntinuity: peple link individual elements tgether s that they frm a cntinuus line r pattern Perceptual Schema: a mental representatin r image t cmpare with needed t recgnize a stimulus Perceptual Set: a readiness t perceive stimuli in a particular way perceptin influenced by expectatins Perceptual Cnstancies: allw us t recgnize familiar stimuli under varying cnditins - Shape cnstancy: allws us t recgnize peple and ther bjects frm many different angles - Brightness cnstancy: the relative brightness f bjects remains the same under different cnditins f illuminatin - Size cnstancy: the perceptin that the size f bjects remains cnstant even thugh images n ur retina change in size with variatins in distance Perceptin f Depth, Distance, and Mvement: Depth and Distance Perceptin: The retina receives infrmatin in tw dimensins (length and width) but the brain translates int 3 dimensinal using - Mncular cues: require nly ne eye - Bincular cues: require bth eyes Mncular Depth Cues:

7 - Light and shadw: creates depth - Linear perspective: the perceptin that parallel lines cnverge r angle tward ne anther as they recede int the distance - Interpsitin: bjects clser t us may cut ff part f ur view f mre distant bjects - Height in hrizntal plane: clser appears higher in hrizntal plane - Texture: appears finer as distance increases - Clarity: clser is mre clear - Relative size: lks smaller farther away - Mtin parallax: if we are mving, nearby bjects appear t mve faster in the ppsite directin Bincular Disparity: each eye sees a slightly different image Cnvergence: prduced by feedback frm the muscles that turn yur eyes inward t view a near bject Perceptin f Mvement: - the mvement f a stimulus acrss the retina - the relative mvement f an bject against a structured backgrund Strbscpic Mvement: illusry mvement prduced when a light is briefly flashed in darkness and then a few millisecnds later, anther light is flashed nearby the first light seems t mve Illusins: cmpelling but incrrect perceptins errneus perceptual hyptheses abut the nature f the stimulus Experience, Critical Perids, and Perceptual Develpment Crss-Cultural Research n Perceptin: the culture ne grws up in helps determine the kinds f perceptual learning experiences peple have. Crss cultural research can help identify which aspects f perceptin ccur n all peple, regardless f culture.