perception Flashcards
how much do we use our brains
brain weighs 2% of body
accounts for 20% of daily energy consumption
about 20 billion neurons in the cortex
each neurons makes thousands of connections
about 20 trillion connections in the brain
which part of the brain is related to sensation and perception
back half of the brain
what is perception
information processing
what is the first step in perception
sensation
sensation is transduction
what is transduction
turning one signal into another
what is sensation
changing physical stimuli in the world into electrical signals in the brain
how many sense are there and why do we define it as this many
5
as there are 5 visible sense organs
how is an alternative way at looking at how many sense are there
look at physical sensation that are transduced by the body
list full set of transduced stimuli = senses
chemoreception - smell and taste mechanoreception - pressure / vibration proprioception - muscle location thermoreception - temp equilibrioception - balance photorecption - vision nocioception - pain audition - hearing
what the brain does for perception
the brain filters sensory information
the brain constructs the world we perceive
sensory information is ambiguous - why we fall for visual illusions
what is rationalism - in terms of perception
some propositions are knowable by us by using intuition alone; still other are knowable by being deduced from intuited propositions
what is empiricism - in terms of perception
we have no source of knowledge other than sense experience
keu=y concepts on vision from democritus
vision is done by the eyes and slo the soul
vision is one of the many sense
things come into the eye and are transmitted onwards
some colours are special
all other colours can be made from combinations of the special colours
colour is a relagive, not an absolute sensations and depends on the relations of objects tp each other
kwy concepts on vision from plato
colour and vision are very complicated
you cannot predict how colours will mix to make other colurs
even if you could you shouldnt
alhazen’s views on colour/vision
you do not see as a result of things coming out of your eye
neither does matter enter your eye
instead light rays originating at each point on the surface of an object, carry information to you
light travels in a straight line
white light is composed of many colours
who tried to understand colour in europe in the 1600s ish
artists
da vinci
then newton tried
how did newton try to understand colour
what did poking his eye with a needle tell newton about the experience of colour - not much
then he experimented on colour in light
theory - white light is pure, gets colured by prism
prediction - placing another prism in front of coloyred light should add more colour
result - white light is made from the coloured light
=falsification of prediction from precious theory
= his paper on optics
key concepts on vision from newton
white light contains a combination of many spectral colours
light of a single spectral colour contains just one wavelenght - bigness
the colour of objects is a result of their reflectin certain combinations of spectral lights - if only a single wavelength is present, only a single solour can be seen
only three lights required to match any observed colour
3 primary colours
what were people starting to work out
but what ere they missing
many people were discovering that all colours could be produced by combination of three wavelenghts
but they didn’t know why
the missing key was trichromacy
name three people who were working out the trichromacy thing
palmer
lomonosov
thomas young - we named the theory after him but he didnt really care about understanding light…
what are metametres
stimuli that are physically diffferent
but are perceived to be identical
what is the central result of colour vision theory
the trichromacy of colour mixing is due to the fact that we have three types of photorecpetor
subtractive colour mixing - why does something look blue
because it absorbs (subtracts) most of the long wavelengths and some of the medium wavelengths. the short and medium light that is reflected to the eye appears blue
so basically it reflects blue light and absorbs the other wavelenghts
colour mixing - why does a patch look green
mix the two pigments together and what you have lft when each has subtracted its wavelenghts are some remaining medium wavelengths that look green
additive colour mixing
mix lights together and what you get is the addition of the light being reflective off the surface
you can get additive mixture from paints
what is the principle of univariance
the response of a photoreceptor is a function of just one variable (number of photons absorbed). thus this response can be identical for
- a weak light at a wavelength of peak sensitivity
- a strong light at a wavelength of a lower sensitivity
how do we see a different colour
you need to compare difference between the L M and S cones
key concepts of young-helmholtz
you can match any visible colour with a combination of three spectral lights becuase
3 classes of light detector in the eye
all colours are represented by the amplitudes of responses in these three photoreceptors
there are infinitely many spectra that will give rise to the same colours - these are called metametres
but there seem to be four unique hues (6 if you count black and white)
opponent processing - what
who came up with it
there are three cone types
but there seem to be four unique hues - 6 with black and hiwte
three cones can code three pieces of information about a stimulus - think of them as three coordinates in a cone space
ewald hering
seeing opponent processing through adaptation
neurons adjust their firing to adapt to the average stimulus
for colour this happens in the retina - the different cones adapt to the colour they are sensing
normally when a neutral background is shown opponent channels are balanced and respond around 0
after adapting they now respond less than they otherwise would have
this reveals which colours are opponent
how would we expect opponent processing to work and why does it not quite act like this
dimesion of colour space to be determined by 3 axes as three photoreceptor classes. so would expect 6 end points
but cones do not have nicely-spaced absorption spectra
L and M cones are especially close so they convey almost the same information
this is very inefficient (think of it as bandwidth out of the eye is expenvie as more wires = fatter optic disk = thicker nerve fibre layer = expensive to build, more to maintain, more to go wrong
so M L and S cones signal by using the differences between the cone responses
how opponent processing works in humans and other old world primates
three receptor types
three dimensions of colour vision constructed from different combinations of those cones
L-M: called opponent red/green axis signals differences in the quantal catches of the L and M cones
L+M: the luminance axis - signals the sum of the L and M cone catches
S-(L+M): an opponent blue/yellow axis
pattern colour interactions
colour is visible over a limited range of spatial-temporal frequencies
pattern colour interactions
-when luminance changes edge is visible
even for high frequencies
-when colour changes it is difficult to see bounday, especially for high frequency patterns
colour blindness - when
generally happens when individuals have missing or abnormal opsin genes
almost always the genes involved are the L and M cone opsin genes
because there are on the X chromosome, men are affected by colour blindness far more than women - men have no backup gene to rescue them if something goes wrong
what is colour vision
it is not usually the absence of colour
instead people lose a single dimension of colour
most common deficit is anomalous trichromacy where discrimination is poorer along the red/ green axis but still present
rarest type (<1 in 1000) is trianopia where individuals lack functioning s cones
losing either of the L or M opsins damages opponent what systems leaving which systems
red green damaged
blue yellow left
losing the S cone leaves only which system
red green`
what does protanopic mean
lost L opsin
what does deuteranopic mean
lost M opsin
what does trutanopic mean
lost S opsin
who was john dalton
chemist
described his own colour blindness
dies 1844
donated hi eyeballs to science
DNA from his preserved eyeballs was sequenced mid 1990s
found to lack an M opsin gene
we now sometimes call lack of M cone daltonism
colour deficits can be stimulated
brettel vienot and mollon 1994
computersied stimulation of colour appearance for dichromats
matching the internal precept can be hard. one solution is to use people who are colour blind in only one eye and ask them to match percepts between the stimulation in the good eye and real thing in the bad eye
online simulations also exist
ecology of colour vision (animals)
many animals only have two photoreceptors L and S
these animals often habe one colour channel and one luminance channel
this can distinguish light vs dark and blue vs yellow but not green vs red
primate colour vision
trichormatic vision exists in both old worls primates and new world primates
but in old world (african) it is present in all animals - X chromosomes have gene duplication of an L-cone pigment to generate an M-cone pigment
in the new world, only females can be trichromats: they carry different cone pigments on their X chromosome and these are expressed randomly through X inactivation
how had primate colour vision evolved
to support frugivory
the eating of fruit
in this sense primates are useful to trees just as honeybees are to flowers
trichromacy would also be useful in identifying edible foliage (old world monkeys) - perhaps both factors are important
the visible spectrum of light is a small part of ….
the wide range of wavelengths in the electromagnetic spectrum
wavelength of light is …
a continuous variable
photoreceptors in the retina are sensitive to a single wavelength?
no
what is motion perception good for
determines motion of objects in the world
attracts attention
figure-background segmentation
estimate depth - motion parallax
infer from and 3D structure
bio motion can be used to infer action and type of actor
5 types of motion
ego (self) - motoin induced by the movement of the observer
object - movement of objects in the world
apparent motion - when a stationary object appears to be moving
biological motion - specific motion patterns of living things
motion parallax - depth from motion
what are the components of motion
depth
speed
velocity is a vector, vector’s direction = direction of motion, vectors size = speed
what us motion aftereffect
the illusion of a stationary object that occurs after prolonged exposure to a moving object
what does the existence of the motion aftereffect suggest
an opponent processing systme like that of colour vision
what are interocular transfer
the transfer of an effect (EG adaptation) from one eye to another
what does interocular transfer tell us about the locys of the MAE in the visual system
result of activities of neurons in a part of the visula system where information collected from two eyes is combined
input from both eyes is combined in V1
recent studies - locate site of motoin aftereffects more precisely
what is optic flow
flow field induced by motion on the retina
arrows indicate direction of motion and speed
optic flow patterns differ whent he observer moves and when something in the scene moves
how should we think about how to process motion information
eg models for motion detection (what are the models, don’t explain)
spatiotemporal energy models for the perception of motion
elabotaed reichardt detectors
model of human visual-motion sensing
in terms of axis how should we think about motion
motion is like orientation but in time
important features of a motor detector
like an orientation detector
but involves changes in position over times
so strat with two adjacent receptors separated by a fixed distance
the two big problems of the motion detector
correspondance problem - which feature in frame 2 corresponds to a particualr feature in frame 1
appeture problem - when a moving object is viewed through an aperture (receptive field), the direction of motion of a local feature or part of the object may be ambiguous
saccadic supression - reduction of visual sensitivity that occurs when one makes a saccadic eye movement; eliminates smear from retinal image motion during an eye movement
how does the motor system solve the problem of why an object in motion may appear stationary
sends out two copies of each order to move eyes
one copy goes to each eye muscle
another efference copy goes to an area of visual systme that has been dubbed comparator
comparator can then compensate for image changed caused by eye movement, inhibiting any attempts by other parts of the visual system to interpret changes as object motion
what did Newsome and Pare discover
experiment with mokeys
trained mokeys to respond to correlated dot motion displays
activity in MT is directionally selective
activity in MT also corresponds with monkeys behaviour
MT areas of monkeys were lesioned
result - monkeys needed about ten times as many dots to correctly identify direction of motion
the man who couldnt see motion
what
akinetopsia - a rare neuropsychological disorder in which the affected individual has no perception of motion
is caused by disruptions to the human cortical homolog of MT
man sees streams of multiple frozen images
as soon as motion is ceased the images collapsed into each other
what did gladstone notice about homer’s writing
didnt use blue, just wine-dark to colour the sea
used several weird terms to describe colour
what was whorf’s idea on language (overarching idea)
language influences cogntion
the words you use shape your thoughts
stronger and weaker forms of this hypothesis
what is the weak version of whorf’s idea
language primes thought
language that has obligatory gender terms may encourage its speakers to pay more attention to gender
languages with stronger tenses may encourage people to attend to time more
words with more than one meaning may prime people to adopt different assumptions
what is the stronger version of whorf’s idea
language contrains thought
if you dont have a word for it its harder to think about
what is the strongest version of whorf’s idea
language alters percetion
words can alter what you hear, see or remember
if you dont have a word for a colour for example you cant see it?
the sapir-whorf hypothesis
all three forms of whorfs idea are supported by some experimental evidence
it is also true to say language is not a tight constraint on human cognition
you can still see blue even if youre from ancient greece
gender in language
german and spanish both assign genders to objects
spanish observers assign gender traits to objects
gender in memory
people given object-name pairings to learn remember them better if its consistent with the appropriate gender
german speakers learn the apples name is patrick easier than if its patricia with the reverse for spanish speakers
even if testing proficient english speakers in english
how do english speaking children tend to assign gender terms to objects
male as artifical
female as natural
language perception
direction terms
spatial terms influence time perception?
-kuuk thaayorre language spoken by people from northern australia
- these and many other groups have an excellent sense of direction
- positions are given in absolute terms rather than relative
is this really an effect of lnaguage or something else?
-in english we dont order time left to right linguistically, left to right is determined by writing
for kuuk thaayorre speakers direction may be a fundamental concept influencing language not the other way round
strong whorf - colour perception
what experiment was carried out
different languages, cultures have many different numbers of colour terms
the berlin kay world colour survey
24 native speakers of 110 unwritten languages were asked to name each of 330 munsell chips
identified languages with between 2 and 11 unique colour terms
different languages, cultures have many different numbers of colour terms
strong whorf - colour perception
what does this say about colour perception in relation to language
does your colour vocab alter the way you see? - yes
when tested at a coarse level there is little difference in colour discrimination acorss cultures
but there are top down influences on colour perception
discrimination across perceptual categories are better than within a category
language influences perceptual categories and maybe only in the right visual field
how do all languages tend to develop names for colours and in what order
2 names - light/warm vs cool/dark
3 names - white, red/yellow, black/blue/green
4 names - white, red/yellow, black/blue, green
5 names - white, red/yellow, black/blue, green, pink
scientific study - what is it tending towards
towards reductionism
methodology required that the phenomena under study be measureable
biological phenomena and behavioural responses are measureable
but personal experience of perception is not measureabel
what is psychophysics
the scientific study of the relationship between physical stimuli and the psychological effect of these stimuli
this field has developed highly controlled mechanisms to investigate this
these methods have wide applications across the physical and social sciences
what is webers law
the ratio of the difference threshold to the background intensity is a constant
your ability to detect a difference is best thought of as a percentage difference
what is a psychometric curve and what is it trying to do
characterses the relationship between a physical stimulus parameter and the probability to detect the stimulus
what are the four results in the medical world
diagnostic test positive vs negative
against
disease condition vs no disease condition
hit = positive result and disease is there
correct rejection = negative result and disease is not there
type 1 error = positive result and no disease
type 2 error = negative result and disease is there
what does type 1 and errors have to do with the study of perception and psychophysics
shows how we need to ask participants the right questions
if we just show one stimulus and see how often people get it right we would only have part of the story