Perception Flashcards
what is akinetopsia - case study LM
unable to perceive motion
very specific of brain is damaged, MT or V5 - prcesses visual motion
what are rods like
sensitive in low light
lower acuity
colour blind
periphery of the retina
what are cones like
need more light
higher acuity
colour sensitive
in the fovea
are there any cones or rods on the blind spot
no
is where the optive nerve is
explain the cells in the eye that transduce light to vision and begin relay to the brain
photoreceptors (cones and rods)
bipolar cells next
ganglion cells to the optic nerve
what brain areas recieve inputs from the optic nerve
in the thalamus - laternal geniculate nucleus
in the cortex
V1 - primary visual projection area/ primary visual cortex in the occipital lobe
explain what areas of the brain see what
both eyes process both sides of the world
left visual cortex “sees” the right of the visual field and vice versa for the right
what is lateral inhibition
occurs in cells in the retina
each active cell inhibits its neighbours
this emphasizes the edges of stimuli
so strips of gradually getting lighter shades of black
which side of the bar appear darkest
the one next to the darker colour as patterns of lateral inhibition between neighbouring cells on the retina lead to that edge being enhanced and so appearing darker
where do we place a single cell recording and what can we define about cision from it
electrode placed just outside a neuron in the animals optic nerve or brain
used to define the cells receptive field
what is the receptive field
the size and shape of the area in the visual world to which that cell responds
what did Hubel and Weisel discover
specialized neurons in the brain with distinct receptive fields
eg centre surround cells - stimulus in centre = higher firing, stimulus in surrund = lower firing
what do edge detectors do
receptive to lines of particular orientation
-horizontal and vertical are the most common
explain parallel processing
divide and conquer
different cells process different areas of the visual world and different brian areas process this all simultaneously
explain the role of the “what system” in parallel visual processing
identification of objects
occipital-temporal pathway
explain the role of the “where system” in parallel visual processing
locations of objects and guiding our responses
occipital-parietal pathway
what happens when occipital-temporal pathway is damaged
visual agnosia
can describe object when shown it but cannot tell you what it is
dissconnection between object and recognition
what happens when the occipital-parietal pathway is damaged
problems with reaching for seen objects
what do parvocellular cells do
specialized for spatial analysis and detailed from
what do magnocellular cells do
specialization for motion analysis and depth perception
what is the binding problem
parallel processing splits up processing of our world
but we do not see the world as disjointed
explain three things that help us solve the binding problem
spatial positioning - reassembling of pieces of references position
neural synchrony - rythm of neurons that are firing in response to the same item tend to be in sync
attention is crucial for the binding of visual features - when attention is overloaded people make conjunction errors
simply no definte answers yet but this is some evidence
explain conjunction errors
seeing a blue H and red T but reporting a red H
define sensation
absorbing raw energy through our sensory organs
define transduction
conversion of this energy to neural signlas
define attention
concentration of mental energy to process incoming information
define perception
selecting, organizing and interpreting these signals
give a brief overview of going from sensation to perception
energy contains info about the world (but noisy, distorted etc)
accessory structure modifies energy
receptor transduces energy into neural respinse
sensory nerve transmits the coded activity to the CNS
thalamus processes and relays the neural response
relayed to specialized areas of the cortex
perception of the world
what is perception
the process of recognising, organizing and interpreting information from the sense
it is no an exact copy of the word
based on our past experiences and expectations
name two types of processing and how they work
bottom-up -perception starts with the senses -incoming raw data -energy registering on receptors top-down -perception may start in the brain -person's knowledge, experience, expectations shape perception
explain the recognition by components theory
bottom-up theory of object perception
we perceive objects entirely by perceiving their elementary features
geons - 3D volumes
objects are recognised when enough inforntaion is available to identify objects geons
explain a piece of evidence that support biedermans recognition by components theory
perceptually degraded picture are better recongnised when geons are preserved
explain the three things that makes geons special
discriminability - geaons can be distinguished from other geaons from almost all viewpoints
resistance to visual noise - geons can be perceived in noisy conditions
distinctiveness - 36 geons have been identified
how geons are there
36
how does top down processing generally work
making inferences based on context, guessing from experience and basing one perception on another
quick
automatic
not conscious
explain one study that showed top down processing
multiple personalities of the blob
blurry pictures all ask you to identify three blobs from three diff blurry pictures
each blurry picture makes you think the blob is something different when in fact it is exactly the same blob just rotated each time
explain helmholtz’s theory of unconscious interference
1860
top-down theory
some of our perceptions are the result of unconscious assumptions we make about the environment
we use out knowledge to unform our perceptions
we infer much of what we know about the world
likelihood principle - we perceive the world in the way that is most likely based on our past experineces. this is especially true when we dont have all the information so have to make some kind of inference
explain the yanny vs laurel evidence
botoom up process - ability to hear certain frequencies (correlated with age) played a role
top-down processes contribute to interpretation as well - previous experiences with the words, accents etc
how do we percieve size with distance (explain both TD and BU)
bottom-up - size of image on the retina
top-down - the perceived distance of the object, the size of the object relative to other objects in the environment
what is special about what hits the retina in depth perception
its a 2D image
depth perception allows us to create mental images of objects in 3D and to judge distances
it is present at least in part at birht in humans and other animals
explain the visual cliff
test of early 3D perception
most infants refuse to crawl across the visual cliff
depth cue - pattern on the floor
when they cannot crawl thery perceive it and get interested from as young as 6 weeks old
social has a big context - will do what mums face tells them
overall though there is fear of the visual cliff - so seems to perceive a kind of cliff so possess depth perception
define binocular cues
our two eyes help us perceive depth
explain retinal disparity
by comparing images from the two eyeballs the brain can calculate the distnace to the object being viewed
used by 3D filmmakers
is a bottom-up cue of depth perception
what distances can retinal disparity differentiate between
1 to 10 ft
what distances can monocular cues differentiate between
10 to 100 ft
what are monocular cues
top-down cues of depth - they are based on knowledge w ehave about the world
explain some things monocular cues help us with
relative size interposition relative motion light and shadow (this we learn) linear perspective
perceptual constancy
size shape brightness colour things look different depending on the angle, distance and lighting however our perception is constant
size constantcy explaine
we perceive the size of an object as constant from different distances
retinal size will be different but we perceive the size as constant
but context matters (eg moon illusion)
brightness / colour constancy
colours may be the same but depending what they are next to changes our perception of their brightness and color
eg the dress
form perception and perceptual organization - old and new view
old = structuralism - perception involves adding up sensations new = gestalt - the perceptual whole is more than the sum of its parts
form perception - how do we knoe where one object ends and the next begins?
figure-ground= organization of visual field into objects that stand out from their surroundings
groupings - the perceptual tendency to organize stimuli into meaningful groups (gestalt principles)
name the 5 laws of peceptual organization
law of good continuation/ continuity law of good figure/ simplicity law of similarity law of proximity law of closure
explain the law of good continuation
we tend to see shapes/ lines as being continuous even when occluded
explain the law of good figure
every stimulus pattern is seen so the resulting structure is as simple as possible
explain the law of similarity
similar things appear grouped together
explain the law of proximity
things near each other appear grouped together
explain the law of closure
we tend to perceive closed figures rather than incomplete ones
positives and negative of gestalt laws
often provide accurate informtion about properties of the environment -refect experince -used unconsciously -occasionally misleading gestalt laws are heuristics
explain the interactive neture of perceptual areas
remeber parallel processing
brain areas for basic visual features interact with brain areas for large scale form
object recogition - feature models
might begin with features
features - small elements that result from the organized perception of form
feature detector neurons in the visual system
what are the advntages of feature based models of object recognition
building blocks
commonalities for variable objects
evidence - play a role in visual search
what is feature search
can use one feature like colour to find target
what is conjunctive search
need to find combination of features to find target (colour and shape for example)
what is serial search
search every stimulus one by one for target
reaction time depends on display size
what is parallel search
target stimulus pops out from the rest
reaction time does not depend on display size (or is dependent to a much lesser degree
neurological evidence for feature based object recognition
parietal cortex damage results in difficulty judging how more than one feature is bound together in objects
either in
-integrative agnosia (parietal cortex damage).
-disruption of parietal cortex via transcrannial magnetic stimulation (TMS)
in both cases subject can do a feature search but not a conjunctive search
methodology for investigating word recognition
words presented very briefly (10-50ms) then masked
mask = jumble of letters / symbols that stops visual processing of the presented word
three important findings about word recognition
word frequency effect - high frequency words recognised better
- repetition priming effect - recently viewed words recognized better
- word superiority effect - letters recognized better in the context of a word
errors in word recognition are driven by…
probability
likely to misread words predictably
TPUM = TRUM or DRUM
reverse errors however are rare - we dont take the pronouncable to the non-pronounceable
what are feature nets
one possible way the visual system recognises words
simple feature detects lead to letter detectors lead to word detectors
sometimes referred to neural networks, have receptive fields and fire above a threshold
but detectors do NOT represent individual neurons, more like a complex assembly of neurons
how does the feature net explain repetition priming
recent firing = higher starting activation level
-frequency leads to higher recency
-repetition increases recency
if the node has fired recently it is easier for it to fire a second time
how does feature nets explain word superiority
must add a layer to feature nets - bigrams = grouping of two letters before letters put to make word (this addition is disputed by some researchers
explain McClelland and Rumelhart’s 1981 model of word recognition
a descendant of feature nets
mushc more complex feature net with feedforward and feedback loops
excitatory and inhibitory connections
more like a brain
what is the ventral stream
visual paths in the temporal cortex
specialised for identifying and recognising objects
what is the dorsal stream
the visual path in the parietal cortex
helps the motor system to find objects and move towards them
how do we use dissociation logic to understand complex systems in the brain
bascially studying malfunctions in the brain
dmage to different areas of the brain cause very different deficits so can conclude that area is necessary for a specific function
eg brain ablation allows scientists to damage specific areas of otherwise normal brains (monkeys or cats) = controlled damage allows for clear conclusions to be drawn
explain single dissociation
one funciton is lost, another remains
so has what but not where
this would show that what and where rely on different mechanisms, although they may not operate totally independent of one another
explain double dissociation
requires two individuals with different samage and opposite deficits
indicates that the what and where streams must have different mechanisms AND operate independlty of one another
Go over slide 87 with podcast
done
what is visual agnosia
the inability to recognise objects despite satisfactory vision
what areas of brain damage can cause visual agnosia
there are many types of visual agnosia
occipital
temporal
parietl
explain patient CK
brain damage leading to visual agnosia
explain case study DF
carbon monoxide poisoning = damage to temporal lobe
could not visually match card orientation BUT could mail card - so orientate a card through a slot
dissociation between judgin orientation and coordinating vision and action
-other patients with parietal lobe damage have opposite pattern
the what pathway is for ….
the where pathway is for ….
what = perception where = action
what is prosopagnosia
type of agnosia = face blindness
damage to fusiform gyrus of the inferior temporal cortex
object recognition in tack but there is face blindness
different to Capgras
houses and faces experiment that shows different objects may have different recognition systems
faces much worse at recognising upsidedown compared to houses
holistic processing of faces experiment
composite faces (so top half one celebrity and bottom half another)
harder to process just one when the faces are aligned than off centre
shows we process faces holitically
grandmother cell experiment
single cells have been found in human MTL that fire selectively for certain faces
so jennifer anniston neuron found
used single cell recording in humans who were undergoing surgery
some cells also have preferences for animals, objects, scenes
grandmother cell? most likey not but coding is more sparse than we previously believed
so do we have a separate “face system”
not necessarily
difference in processing appear when
-interpreting faces
specific indivisuals have to be recognised
-confirgurations of component parts are importnat
expertise!!
explain Gauthier et al’s Greebles
showed a significant increase in fusiform face area response to greebles after visual discrimination training - so had taught face expertise in greebles
top down processing occurs ………..
in frontal area before bottom-up activation in occipital area when it is necessary
