Perception Flashcards
signal detection theory
basic perceptual task is to determine if a stimulus is present or absent
Signal detection theory outcomes
hit
miss
false alarm
correct rejection
Hit
target present
respond ‘present’
miss
target present
respond absent
false alarm
target absent
respond ‘present’
correct rejection
target absent
respond ‘absent’
hit rate
= hits/hit + misses
accuracy when the target was there
false alarm rate
= false alarms / false alarms + correct rejections
sensitivity
ability to discriminate signal from noise
- depends on distinctiveness and variability of internal responses (overlap distributions)
bias
tendency to provided one answer over the other
- say present or absent when you are unsure
- depends on where the response criterion is
- depends on how lopsided the evidence must be to say that the target is ‘present’ or ‘absent’
What you need to determine sensitivity and bias
hit rate and correct rejection
- need one number from the top and one from bottom
signal detection theory graph
when target is present will get a large number
response criterion
- a line at some value and for any measurement above threshold say present for any below you will say absent
- if you change your bias have to move your criterion
medium sensitivity
overlap
high sensitivity
very little overlap
measurement from target trial is much higher than a target absent
low sensitivity
huge amount of overlap
not good at telling if target is there or not
extreme case they would be perfectly overlaying each other
neutral bias
right in the middle where the 2 distributions cross over
postiver bias
criterion is pushed up to a higher number
- closer to target present
negative bias
criterion is pushed down to a lower number
- closer to target absent
- lots of hits, very few misses but will also get lots of false alarms and fewer correct rejections
sensitivity equation
d’ = Z (hit rate) - Z (false alarm rate)
- d’ = distance between the 2 distributions in standardized coordinates
- 0 = no discrimination, can’t tell distribution at all
- larger value = better discrimination
bias equation
C = - Z(hit rate) + Z(false alarm rate)/2
- <0 bias from ‘present’
- 0 no bias
- > 0 bais for ‘absent’
downward trend
hit rate and correct rejection rate get worse as noise increases
direct perception theories
- bottom up processing
- perception comes from stimuli in the environment
- parts are identified and put together, and then recognition
constructive perception theories
- top down processing
- people actively construct perceptions using information based on expectations
bottom-up processing
recognition by components theory
- irving biederman
- perceive objects by perceiving elementary features
- geons: 3 dimensiona volumes
- objects are recognized when enough information is available to identify objects goons
geons
- discriminability (can be distinguished from other geons from all viewpoints)
- resistance to visual noise (can be perceived in ‘noisy’ conditions
- invariance (recognizable no matter the illumination direction, surface markings, and texture)
- distinctiveness (36 different geons)
principal of componential recovery
the key to object recognition is not the amount of information but the ability to identify its components (geons)
- found that objects with recoverable goons error rates were lower
multiple personalities of a blob
perceive the blob differently in different environments, not just the shape
bottom up theory
context matters
top down processing
constructive perception
- inferences based on context (surrounding elements of the visual scene)
- guessing from experience (knowledge and expectations based on the past)
perceiving size
- perceived size is a function of both bottom-up and top down processing
- bottom up (the size of the image on the retina)
- top down (the perceived distance of the object & the size of the object relate e to other objects in the environment)
distal stimulus
the thing we are looking at out in the world
proximal stimulus
the light/sound landing on our eye/ear drum
percept
what we perceive, not a physical thing out in the world but a mental thing
job of perception
infer the distal stimulus given only the proximal stimulus
Helmholtz theory if unconscious inference
- top down theory
- our perceptions result from unconscious assumptions we make about the environment (use knowledge to inform our perceptions)
- we infer much of what we know about the world
- likelihood principle
likelihood principle
we perceive the world in the way that is ‘most likely’ based on our past experiences
gestalt psychology
- the mind groups patterns according to laws of perceptual organization
- these ‘laws’ are heuristics based on what usually happens in the environment
- built in nature of there laws
heuristic
= rule of thumb
- provides best guess solution to a problem
- fast
- often correct
Apparent motion
‘the whole is greater than the sum of its part’
perceive that the 2 lights flashing are seen more as a single light jumping back and fourth from the 2 locations
law of good continuation
lines tend to be seen as following the smoothest path
- all things being equal lines continue on a straight path
law of good figure (simplicity)
every stimulus pattern is seen to the resulting structure is as simple as possible
- olympic rings (5 interlocked rings or a bunch of odd shapes beside each other)
law of similarity
similar things appear grouped together
- one big unified group vs lines
law of proximity
nearby objects appear grouped together
- one big group vs separate sets
law of closure
separate elements will tend to be grouped to form closed figures
- circle vs box
law of familiarity
things are more likely to form groups if the groups appear familiar or meaningful
gestalt laws of perceptual organization
law of good continuation law of good figure law of similarity law of proximity law of closure law of familiarity
physical regularities
- oblique effect
- light from above assumption
oblique effect
people can perceive verticals and horizontals more easily then other orientations
light from above assumption
light casts shadows from above, providing specific information about depth and distance
- use shadows as depth cues
semantic regularities
- scene schema
the knowledge of what a given scene ordinarily contains (doctors vs lawyers office)
meaning & context
bayesian inference
your conclusions should depend on both your prior beliefs and the current evidence
bayes’ theorem
P(H) x P(E|H)/P(E) = P(H|E)
H
hypothesis
E
evidence (the observation)
P(H)
prior probability (how likely is hypothesis h before considering the evidence)
P(E|H)/P(E)
likelihood (how likely is the evidence e given the hypothesis h, compared to how likely the evidence e is overall
P(H|E)
posterior probability
- how likely is hypothesis h given the evidence E
ungerleider & mishkin
lesion in anterior temporal lobe region
- perform poorly in object discrimination and good in landmark discrimination
lesion in posterior partial lobe
- good in object discrimination and poor in landmark discrimination
single dissociation
single - one type of damage
dissociation - performance differs across 2 tasks
double dissociation
made of 2 single dissociations
- double = 2 types of damage
- dislocation = performance differs across 2 tasks
- gives strong evidence that different brain areas are involved in processing for those 2 tasks
what pathway
- identify objects and why we might use them
- temporal lobe
- ventral pathway
- occipital to temporal
- vision for perception
- v4: color processing
where/how pathway
- where that thing is in the world and who we interact with it
- parietal lobe
- dorsal pathway
- occipital to parietal
- vision for action
- v5: motion processing
‘what’ vs ‘where’ in humans
patient D.F.
- damage what
- bad at match orientation
- good at putting mail card in slot
balints syndrome
- damage where
- good match orientation
- bad at putting mail card in slot
Balint’s Syndrome
- disorder of space exploration and space cognition
- a cluster of co-occuring visuomotor & visuospatial disturbances
- results from bilateral posterior partial damage (dorsal stream)
Ebbinghaus illusion
perceptually different
physically identical
- people will say that they are different size but they are same
“reverse” Ebbinghaus illusion
perceptually identical
physically different
- will say same but they are different
- in order to make identical have to make one larger
- grasping action reflects actual size
ponzo illusion display
bar on right false appears longer than bar on left
- effects the ‘what’ stream
- bar on right is actually shorter
- control display (no illusive context) shows bar on right correctly appearing shorter
- perceptual estimation reflects apparent length
- grasping action reflects actual length
action facilitates perception
moving can change our point of view, which can aid our perception
- ex: disambiguating a degenerate view of an object
perception facilitates action
perception informs us of
- what to act on (perceive cup)
- how to act on it (reach for cup)
during performance of actions, perception
- provides feedback on progress and success (grasp for cup)
affordances
possible actions an individual perceives as being available due to an object
when we look at an object
- perceive its physical features (colour, size, shape..)
- perceives its affordances for action
- these affordances can then influence our actions whether it is beneficial or not
