chapter 4 Flashcards
blue dress
universla agreement that ppl differ in. their perceptions
some ppls brains inetrpeted the shades of dress as represneting true colours but others brains inetrpreted them as the effects of lighting, relfections or shadows and adjusted eprcpetion accordngly
sensing isntthe same as eprceiving
sensing
sensation occurs when our sensory organs receive stimulus energyoes from envinrment and convert them into electrical enegry of nervous system
conversion is called transduction
electrcail signals generated are then sent to the brain via sensory nerves
perception
refers toe further processing of tehse elctrical signals, including organzing, constructing, and interpreting sensory info - all to form a representation inside the brain of what it thinks is on the outside
althogh eyes and otehr sense organs detect stimli, what the eyes see or nose smells doenst alone dtermine our concious percpetions
percetpton is the job of the brain and perceptions arent direct copies of sensory world
they are our brains beliefs abt sensory world based on prior expericnes and present sensory evidence
transduction
process of trasnduction into eletrical energy is diff for each sensory organ
through the sensory specific process of transduction, light for ex activates receptors in eyes not in teh ears and even though they respond to diff tsimuli they sned same kind of eletrcial signals through nervous sytem to brain
how nerves connect to brain matters
the visual cortex resides in occiptal lob, the autodry complex in the temporal and the somatosensory in parietal etc.
its not the stimuli itself that allows for unique sensory qualities but aslo how tehse stimuli activate the brain that detrmines how theyre perceived
in this way teh rbain reps a compelx world through multiple sensory channels to create diff qualiies of expereince
sensations merge in the brain to determine percpetual experiences of things
brains use all info at disposal to make educated gueses - usually sensory systems provide complete and accruate pic of world we inhabit
psychophysics
Fechner developed a set of methods to objectvely measures ppls subjective perceptual expereinces
field called psychophyics focuses on the relationshup between the phsycial charctericstc of envrinmental stimuli (like mag) and our mental experience of them (like perceived intensity)
not all info our senses detects results in concoius perceptions
absolute thresholds
the minimum amount of stimuluation a person needs to detetc the stimulus half of the time
shows the trhehold of perception
threshold is opp of sensityvty - lower the threshold, higher your sensitivty
the fact that threshold reps the ability to perceive a stimulus 50% of time means that thresholds arent static but constantly changing
this uncertainty makes perception probalistic such that transotion from hearing to not hearing is gradual
detetcing stimulus depends not only on its strength and perceivers sensity but also on various psycholgical, situational and personality factors which all cause problems for psychophysicist
conservative and liberal response bias
some ppl may wants to be accurate so they dont idenify stimulus unless 100% sure - this is conservative bias
some ppl may lie and say they hear stimulus - liberal bias
signal detetcion theory
explain how we make decisons under conditions of uncertainty
- controls bias that ppl have
hit: stimulus present and respond yes
miss: stimulus present, respond no
false alarm: no stimulus, yes response
correct rejection: no stimulus, no response
signal detetcion theory thus distinguishes conservative bias form a liberal bias allowing researchers to distunsh true perceptual sensitivty from other factors that might ifnclue our responses
the measurment of basic aspect of perception - did you detect something - is infleucned by motivations of perceiver
difference thershold or just noticble difference
the minimum change in a stimulus for an observer to detetc a difference half the time
Weber, observed difference thresholds inc as the stimulus size inc
perceptuon of stimlus change isnt fixued absoluet value but a relative qunatity - a percentage
this observation, perception of stimulus change is proptinal to mag of stimuli is known as webers law
can be applied to perception of any mag change
its a ratio rather than absolute amount of difference
fraction is the ratio fo minimum change in mag of stimulus to overall mag of tsimulus
it can be calculated for any sense suggesting that perception can have lawlike properties
precise value of webers fraction differs for each sense
ex. 5g chnage is notcile on 50 g. for 25kg the change would be 2.5 (ratios are both 0.1 - 5/50 and 2.5/25)
variablity is snese and perception
sensores demonstrate substantial variability within and between ppl
ex. some ppl detct snakes more than spiders etc
results pont to great plastcity of perceptual systems in which neurons chaneg their sensitivty and selectivty with expereince
there si also a huge range of absolute thresholds
dark adaption
eyes becoming adjusted to darkness having a 100k fold increae in visual sensitivty
ratehr than being fixed, the eye cosntantly adpats to light levsl to optmize sensitivty
adaption
all senses adjust to envrinment using adaption which occurs whne stimulus remains constant overtime and eventually seems to disappear
with constant exposure to any stimulus, neurons fire less frequently, a fundemental rpicnple of nervous sytem and sensory receptors
sensory adaptation occurs at level of sensory receptors whiel perceptual adpation occurs higher up in brain
both free us to focus on changes in envriment ratehr thna on stimuli are unchanging
ex. olfactory receptors
aftereffects
conseuqence of adaption - opposing distoruuons that occur after adaptation
opposing ebacsue you perceive the opp of what the senses and brain have adapted to
waterflll illusion by aristotle - after fazing at waterfall when you move gazeto rocks you see them moving upward
aftereffects apply not only to simple sensations but also compelx perceptions
our availiy to perceive otehrs emotions is subject to turning efefcts of perceptual adaption
reduced adaptatuon
central aspect of autism - characteize by altered social communication sklls and repetive behaviours
ppl with autism are diff attuned to envrinment than the average neurotypical person
chatacetrzied by atypical snesory percpetion
decreased aapdtion may contirbute to hypersnesituy
animal kingdom seeing things diff
human snesory systems rep just a few ways to sense of the envrinment
among mammals tehre a huge variety of sneosyr capabilities that have evolved through natrual selection
similar snesoyr organs provide very diff perceptions but very diff sensory pathways can provide siimlar perceptual info
eyes of insects and bees are able to cpature broader spectrum of light than us - this helps them with gather nectar which the colouration in uv light isnt visible to us
aniamls like bats and owl use echolcation to assist with perception of enevrinment
eachoes bucning off suroundings provides mpa of envinrmnet
even though many mmals have similar auditory systems each creatures sytem offers a diff range of audition
we hear middle range of frequenceis and elephants hear low frequencies
we use ear canals to hear frequencies
elephants detetc frequecies through grouns, recptros on feet and trunk
the trunk does mnay things in an elephant
despite varitaion, most species have one dominant sense organ
humans are visual animals
bears are smellers
properties of light
our eyes transduce elecyrmag energy from world into neural energy of brain, trasnofrming light into sight
basic units of electromag radiation called photons have wavelike prooerties
depending on wavelength, electromag radiation is classified into various types of waves from radio to gamma
human eyes detect visible spectrum - a priperty in sensory recptros in eyes allow us to see it
sensoyr recpetros are tuned to range 390nm to 750nm wavelengths
just notcible difference in wavelenth is aroudnsingle nanometer in bluegreen of spetcrum
wavelength is percpetually percieved as hue which corepodns to what we experience as colour
wavelength is related to frequency such that long wavelength is low freq and short wavelenth is high freq
amplutude or max height is related to exerience of intensity or brightness
these two measures distinguish quality (colour) and qunatity (brightnes) of light
colour purity is related to number of wavelengths that makeup the light;it detrmines percpetual quality of colours satruation
eye can distinguish up to few hudned spectral colours which are based on single wavlength or small band of wavelength
beause theyh have small umber of waveenth, spectral colours are most pure and vivid
in nature objects dont reflect any precise wavelength
whne spectrak colours are mixed together or withw hite light this yields vast range of colour experiences we can distinguish
as purity and saturation dercease, clolours fade to grey
more wavlengths the less colouro you see
eyes and retina
light eneters the eye through cornea, the transparent covering at front of eye and passes trough the pupil, a hole in muscle knwon as iris whcih gives distinct colour
irisi can inc or dec the size of pupil to adjust how much light enter the eye
pupil appear balck beause most of light enetring the pupil is absorbed
lens of the ye bends light and uses process called accomodation in hwihc specilzied muscles alter the lens focusing power by changing its thickness and thsu degree to whcih it bends light
as ppl age the lens of eye gets less elsastic and eyes ability to focus via accomdation weakens mkaing it diffcult to see things that ahappen to close
presbyopia
the eye focuses on image by adjusting lens so that light is precisly focused onto small region called fovea in retina on abck of eye
the retina has photorecptors called rods and cones
these convert light energy into electcal energy, a process called visual transduction
nearisghtnedness or myopia involves faraway obejcts being project to far in front of fovea
farsightned of hyeropia involves near object overshooting the bakc of the eye behind fovea
both result in uncofsed imagie on retina and thus blryy vision
photoreceptor cells contain photopigments that are senstive to lifht
human eye uses variety of light sensitve photopgmets to pick up diff waveelnths and covert them into eletrcial signals - range of wavlengths that tehse photopigments respond to dtermine what wavelngths of light species can see - visible spectrim
when light energy hits photorecptor cells the rods and cones - it causes chem changes in light senstive photopgemnst and changes their shape whihc alters flow of ions into and out of photorecptor cell body
this ionic conc generates eletricty which is passed on to layers deper in retina - the bipolar cells and ganglion cells - which fire action poetntails when stimulaetd suffienctly
in turn eletcal signals make it to the brain
to travel to brain, action potentals frm retina coevrage in a bundle of axons called optic nerve forming a thick cable that plugs the eye into the brain
optic nerve connects to eye in specific spot at back of retina
no room for photorecptors where optic nerve leaves the eye which results in blind spot where no info can be reeived
the brain fills in spot with info it gets from surrounding regions of retina
this is conrete illustartion of sendstion and perceptiin
brain uses beilfs of orld, given surrounding contect to perceive
light rays that enetr the eyes are inverted on retina so that up versus down etc are flipped
if sight didnt involve brain then you would see ppl upside donw etc
retina is 2d sheet that can code only flat images
brain uses experience and smarts to reocver whats lost onretina
Rod and cones
two types of photorecptors in cells of eyes and have diff functions
rods all have same photopigment but cones contain one of three varities
multiple pigments of cones allows us to perceive colours - as a reuslt colour vision occurs in the cones
in addituinm the two tyoes of cell are disproptionetly repped in the eye - human eye has 120m rods but onl 5m cone cells
rods and cones also differ on location on retina and resolution capdacity
cones are densly clustered in small centralpit in the back of rteina is called closed fox
during day our vision comes from cones in tiny section of retina
eyes are traiend to move constantly in order to focus diff stimuli direction onto fovea called foveation
acuity is sharpness or specificy of perception, suporting discirmation of stimuli
sensitity is abilitu to simply detetc stimulus is present
cones specilzie in acuity, suporting daytime vsion when light is abudant
rods provide more sensitivty, primarly supoorting nightime vision
farther from the fovea and toward the periphry of retina teh ratio of cones to rods greatly decreases - most rods are in periphery
more rods than cones - reason that rods offer more sensitvty in low light
snesitvy versus acuity also coems down to how tehse photorecptors are wired to the brain
cones in fovea have more one to one conenction to cells fatehr down line showing less conevrehcen onto vipolar ganglia
rods demonstrate much greater degree of convergence ultiatly constrcting many indivudal signals to one ganglian cell
pattern of less coneregcne and greater acuity in cones is carrier over to brain
once info from cones is in brain, visual fortex devotes great deal of real estate to provesing their inpit
all sensyr systems have systemtic distortion called cortcal mag factor where regions tha require more food receive more cortical reps or less coverngence
more direct connections (less convergncE) in conjuftion with mroe cortical space (cortical mag) allowing the cones in fovea to go up or dwon
higher level vision
higher order brain processes assmeble the big picture out of the detials
the brain appears to make sense of the data it reieved form the retina by a process of hierarchal analysis in which higher and higher leevls of brain create mroe and mroe complete represnetaions of what is out in the world
visual info travels along the optic nerve from each eye into the brain
at place called optic chiasm info from each optic nerve diverges - axons coming from left side of each retina are diverted to left hemisphee of brain
axons arrive in specilized visual nucles of the thalamus and then continue on to the primary visual cortex which is the visual sesnory receivng area in the occipital lobe - the primary visual cortex is retintopcally ogrnized meanig that adjacent portion of retina conenct with adjacent areas of visual cortex
the visual cortex recreate pic of actvity presenetd on retina like tv in brain albeit distorted focusing primarily on fovea through cortical magnification - the visual cortex reps the foveal region as if it were looking at it though a high powered mag glass
sicntists used single cell reocridng in animals to messure action potential form neuron to dtermine that certain neurons in primary visual cortex called feature detectors respond to basic features represented across retina like edges, lines or angle
these features may be building blocks of perceptual experience like a periodc table of perception
info form these feature detectors is collected and passed onto team of cells in secodnary visual cortices also known as visual association cortex where objects start to be reconstrcuted
association areas of cortex combine new snesoyr inputs with prior percpetual experiences and knwoeldge abt world
visual asscoiation cortex located at broded of occipital and temproal is where elemnts or visual features like lines and egdes are glues toegtehr and organized into basic shapes
ppl with damage to these regions arent blind but they cant orgnize details of perception into objects - fail to draw basic shapes
the highest level of visual association cortices in the adjacent temproal lobe combines more basic visual features into more complex objects
patterns of neural firing iwthin cells in these regions can help you recgonze specific obkects
ppl with damage to temprla lobe can perceive shapes and can draw them but fail to recognize what the objects are
this is visual agnosia meaning vision without knwoledge
prosopagnosia is uou cant recognize faces
whether one part of brain is devoted to reogning faces or whetehr each part plays an active role is being researcheed
specific paterns of neural activty within visual asscoaition corteces support recognition of partcilar words and objects
the brain may have developed specilized activty for teh analysis of especially imprtant visal tasks
the visual brain may have many specilzied tools for recgoniztion but these tools can be used for new and varied purposes
pathway in visual brain
in addition to udnertsnading what an object is the visual system needs to be able to locate it
although these two capacties are intimatly conencted in experience they are dissociated in the brain
what is it and where is it - these two tasks reflect the two major pathways in visual brain: ventral and dorsal ventral pathways - which orginate from retinal cones and rods
while ventral travels along tempral lobe the dorsal pathway ultimately joins the parietal lob
ventral pathway traverses the underside of tempral lobe and is specilized to adress teh what question
damage to ventral stream impairs recognizng what an object is but leaves intact ability to say where it is
dorsal stream flows upward to parital lobe and is spealized to adress where and how question of object recognition
it supports location, depth and motion and inlfueces how we interact with obkects
indivduals with damages dorsal aptwhays can see and recognize obejcts without knowing where it is or how to grasp it
togtehr these findong reveal double dissaociation - strongest evidence in neaurspych that two functions are suported by distinct parts of brain
although the two visual pathways are uniquely specilized they need to communicate with each other
how they communicate with eachotehr dpeends on focused attention
humans are action based aniamls and we are adpated to perceive motion
percpetion of moveemnt is processes in speiclzed part of brain along dorsal pathway - the middle temproal cortex or area MT
motion eblongs to dorsla beacsue knowing where something is depends on its movement
each MT neuron is tuned to respond to motion in particular direction
some of the neurons will inc their firing response when an object is moving to the left, others when an object is moving up or down; some even respond to complexradial motion
indivdual with dmage to area MT are diagsnosed with akinetopsia a deficit in perceiving motion - they expereince world as series of snapshots ratehr than flow
modern tech in form of tv et.c use illusion known as apparent motion or phi phenomemon to captlize on highly tuned motion detectors of visual system - in this trick, seprate lights or images flashing in rapid sucesion are percived as singular fluid movement
the objective of perceptual system isnt to rpeort what is on sensory surface but to give you a representaion of what it thinks is out in the world by filling in missing pieces
Properties of sound
sound is derived from tiny vibrations that can travel through air, walls and windows
when object moves and vibrates, compressed and expalnded air moelcules create waves that exert pressure on the ear
vibration are too minute for body to feel so the ear evolved to collect and trasnduce them into neural eenrgu which the brain interprets as sound
we call waves created by stimulus sound waves but sound doesnt come from stimulus but only in the perceivers mind
auditory rceeptors are senstive to only a certain range of waves
our range of audition narrows with age causing us to miss mroe high pitched sounds in venrinment
sound is derived form air pressure and compression, the frequency of whihc is the number of wavlenths compelted per second
sound wave in hz
we hear from 20-20k hz
the higher the freq of a particular wave, the higher the sounds pitch - pitch is percpetual quality of sound - quality not quantity of energy
amplitude is related to qunaity of energy and corresponds to intensity of loudness of sonds we hear
sound waves with large amps displace air moelucles mroe than low amp waves dow and this larger displacemt icnreases the eprceived volume of sound
amp in decibals which is dtermiend by ratio of pressure between diff sounds
complexity of waves dtermines the timbre or quality of sound
all sounds are made up of many cumaltive waves
the complexity of sound allows us to experience teh psycholgcial quality of timbre - if you heard two instruments playing same pitch at same vol u can tell the isntruments apart by diff waves which chanegs the complexity of sound
although many sounds in envirnment, the sounds that humans have evolved to hear best are within a freq and amp range that correspond to human voice
over time our hearing apparatus appears to have been ehavily infleucned by social envrinment - humans love to talk and ears have evolved to listen
anatomy and physiology of human ear
the visible section of ear, the pinna or outer ear is sound funnel attached to side of head that has evolved its shape to cpature sound waves
our ears cant move
humans have to rely on structre of ear to better funnel sound into ear canal
once sound waves have been cpatured, the tiny ear canal helps enhance cetrain sound freq and poretcts the very fragile tympanic membrane knwon as eardrum
this membrane is boundary line between oiter and middle ear
eardrum is tight skin like memrbane approx one inch into ear canal that responds to sound wave vibrations by moving in and out with coresspodng presure changes
eardrum is sensitive and repsonds to pressure from vibrations of faintest sounds and to the intense pressure that can be felt when gaining elevation or dividng below
in the middle ear, the eardrum connects to three tiny bondes called ossicles - hammer anvil and stirup form bridge between eardrum and anotehr emrbane called oval window
eardrum connected to hamemr which joins with anvile which conencts to stirrup which arrives at oval window
the ossicles act as levers - they amplfy vibarations of incoming soundwaves
the eardrum adn ossicles act as backward drum - the drum moves mallet to amplify the air pressure waves - this amp is very improatnt for heairng especially at small amp becasue behind the oval window the inner ear is filled with fluid and fluid requires more enegry to move than air
if the sound wavs not amped the quieter sounds that were arent capable of picking ip wouldnt mvoe to the oval window and would be inaduible
the ossicles help protect inner ear from extreme loud noises
mucles that control these bones can dampen vibrations that reach the oval window
oval window which forms boudnary between middle and inner ear is attached to spiral shape strcture called cochlea
cochlea is critical transducer of ear turning fluid vibrations into neural energy
coil of cochlea is filled with lfuid that is moved when ossicles push and pull on oval window
movement of fluid causes basilar membrane to vibrate
bibrations of baslilar memrbane causes tiny hairlike sensory neurons called cilia to bend back and forth
cilia are rganized in rows along basilar membrane
physcal bending of cilia triggers neural impulses
cilia are extermly senstive
bending cilia in one direction causes depolariztaion of hair cell bodies making the more likely to fire action potnetials
bending them in opp cerates hyerpolariztion making them less likely to fire
this pushing and pulling is converted into series of action potentail bursts
axons of hair cells form cochlea are bundled togetehr to form auditory nerve
action potentials from hair cells in cochlea travel through auidtory nerve to brainstem which trasnmits impulses through the auditory nucleus of thalamus up to primary audtory cortext located attop of tempral lobe
before sympony can reach brain the inner ear has to translate indivdual notes
perception of pitch and loudness
as vibrations pass through ear canal to cohclea the waves must somehow be seprated by pitch and loudness allowing us to distinguish things
one theory of pitch perceptuon, frequency theory, proposes that the brain uses the frequency of hair cell firing to ndicate pitch
ex. sound wave at 20hx enetr cochlea its transmitted to audtroy nerve by hair cells 20 pulses per second
this is okay for low freq sound under 100hz where sound wves frq can match freq of neural impluses form auditory nerve
bc neurons need time between firing to produce new action potentials (neural refarctory) ciclia can only fire abt 1000 tims per second
for high freq sounds they are too high for there to be one to one correposndace
volley princple explains shortfall by prosing that neural hair cells alternate firing rate to achieve faster combine frequencies
cilia in cohlea take turns firing so that they can respond to higher frequencies
if neuron needs to respond to wave of 1000hz frew they share load with three neurons so it only fires 250 times per second
freq theroy still doesnt explain how ear seprates freq and ampltidue info so we can distingush pitch and loudness
not only does freq of input alter the freq of hair cell fiirng but the amplitude of sound would do as well
as such larger amp sounds will inc the firing of hair cells
if two diff aspects of stimulus can make a neuron fire how can we tell whats tsimulating neuron
Helmholtz proposed place tehroy of pitch whihc states that diff picthes arise from diff places along basilar memrbane
basilar memrbane evolved to help filter snesory info that travels to brain
helmholtz proposed that high freq are felt by hair at bggeing of basilar memrbane where its narrower and stiffer and low freq travel all the way through the coil to hairs on tip of basilar memrbane wheres its wider and flopier
evidence for place theroy came from Beksy - presneted tones at diff frequeceis and found that narrow stiff end vibrated more to high freq and wid floppy area vibrated to low freq
the basilar memrbane creates a place frequency map
accoridng to place theory, freq (pitch) depeonds on where the basilar embrane is stimulated while amp(loudnesS) depends on how much the basilar memrbane is stimulated
more evidence is that hearing loss - hairs dmaaged becasue of overexposure to sounds - cilia loss occurs at specific locations creating hearing impairments for specific freqs
place tehroy has limitations
low freq sounds arent well organized on basilar membrane as Helmholts has predicted
place tehroy and freq theory proivde clues to how pitch is segreated in auditory system
place tehroy best explains percpetion of high pitch sounds
freq theory best explains percpetion of low pitched sounds
for perception of pitch farther along auidtory system, place freq maps are found in primary auditory cortex
adjacent places on bislar memrbane are represenetd in adjacent parts of primary auidtory cortex, making minds ear
in this tonotopic organiztion, high freqs are processes toward back of auritory cortex and low freq toward the front
whne adjacent locations in human audtory cortex are stimulated before neurosurgery the nearby picthes can be heard
sound localization
has to tell us where it is
localization is imprtnat feature of hearing because its good to know where sound is from
getting input from two ears loacted on opp sides allows brains to compare relative timing and intensty between sounds hitting each ear
the brain then uses this contrast to locate the origin of osunds in space
sound tarveks fast - its amazing brain can calc the tinest difference in the time a sound takes to reach our two ears which are only 6inch apart
brain can detetc 0.0000027 second diff between arrival of one sound at one ear and then at the other
intensity of sound provides own clues
head casts a shadow such that ear furthr from sound gets slightly queiter verson than ear closer to source
we dont hear minute difference intiming or loudness but we perceive it as sound location
sound localization is accurate in humans for obejcts infont because we use visual feedback to tune precision of our loclaization
stero sound at movies takes adavanatge - sound emited form speaers on both sides stimulating natural differecnes between our ears - this creates illuson of movement in theater to help the sound and visual perceptions align
since vision has important role to play in hearing reseacrhers look at how ppl without sight sense enrinment through sound
blind use theri visual cortex during auditory tasks and that their auditory cortex uses altnertive wasy of localizing sounds
without visual experince the brain reorganizes how we hear in ways that respect diveristy and unqnelss of ones expereinces
