Perception Flashcards
3 aspects of perception
- not hieriarchal
- is the interpretation of sensations to make sense of environment
- depends on contextual cuex
colour constancy
how we percieve coour changes depending on illumination, contrast, etc
depth perception
shape
concentrationg
shading
concavity
(HOW WE SEE 3D OBJECTS IN RETINAS 2D STATE)
expectaions affect on perception
previous experience and knowledge of the world infleunces how we see things; especially in ambigious situations
the brain and perception
integrates information from different sensory modalities to produce and interpret
mcgurk effect
multi-sensory perception effect where ther eis a conflict between VISUAL and AUDITORY information
e.g. V vs D vs B mouth shape and sound
ventriloquist effect
a multi-sensory perception effect where visual adn audodoration LOCALIZISATIOn conflicgts;
illusion of thinking sound comes from a dummy even though location of sound is from ventrioloquist
Berman and Weich 1976 experiment
method= played a beep and a flash of light from differet locations and had participants point to where they think the sound came from
results= localization of sound dragged the light
perception as inference
visual system crates accruate, detailed and 3D percpetp frion small, tiny 2d retinal images
how to study perception
- how receptors carry electrical signals using action potentials (raw data)
- how our perspection is subjective and changes contextually (interpreation in the brain)
what is sensation
raw data processed by sensory rerecptors sch as eyes, ears, nose, etc [bottom up]
what is perception
how sensations are processsed and interpreted into the brain [top down]
why do our eyes prefer visual over auditory information
because visual information is more precise than our ears (evolutionary tendency towards vision)
prosopagnosia
neurological disorder that impairs a persons ability to perceive FACES
what is damaged in prosopagnosia
the frusiform gyrus (face recognition area)
parallel processing
processing multiple things at once (depth, colour, etc)
what are perceptual sets
pyschological factors determing how we perceive our environment
what does the v1 detect
orientation/direction
v1 cortical simple cells
oblong reeptive fields to detect tild/directions at specific locations
combine input from multiple ganglion cells
v1 complex cortical cells
correspond to SEPCIFIC tilt/direction ANYWHERE in RF
v1 hypercomplex cortical cells
correspond to particular tilt/direction AND ENDS of a line
retinotopic organization of v1
left to right and right to lef corresponded
v1 is organized into ‘maps’ that correspond to each other
how was cross processining discovred
bullet wounds in soldiers; they could not see SPECIFIC parts in a visual field due to lesions in that area (left or right)
what are blobs
segegrated processing of colour
mach band illusiosn
different brightness bands that contribute to seeing edges as off center/on center cells either fire or illuminate
on centre cells and light
if light covers center= lot sof neuron firing
if light in surroundings= inhibition of firiting
if light in BOTH centre and periphery= some firing
centre surround opponency
occurs in LGN cells= lgn cells change firing rate MOST when they encounter changes in an image to detec edges
why are edges important
correspond to important things (otlines)
recognize objects
used even in computer vision (edge detection algorithims)
dorsal stream: what for
CONTROL of behaviour (“WHERE/HOW”)
ventral stream; what for
CONSCIOUS perception (THE “WHAT)
difference between dorsal and ventral streams
the “WHERE vs WHAT Theory”: how information is used after it arrives
damage to dorsal stream cuases…
optic ataxia
optic ataxia + example
occipital pareital region damage where a woman can’t GRASP an object she sees
affects control of behaviour
damage to ventral stream causes…
visual form agnosia
visual form agnosia + example
patient DF can grasp an object under direction that she can’t regonize due to damgage in ventral prestriate cortex
affects concsious perception
what is visual agnosia
conscious perception of the world and recognition of an object (light, pose, position, etc)
how do we see objects
- different types of objects (light, etc)
- different versions of an object= degraded/ dilluted/noisy, etc
but humans due to edge perception can still recognize often
who was oliver sacks
patient with visual agnosia; can’t identify a rose but uses OTHER ways of identifies it such as memoery and smell
how do we precieve motion
images move into retina
- because we move our eyes
- because the subject moves
what area of the visual system detects motiion
v5/Mt
akinetopsia
lesions/damage to v5 that cause motion blindness; you only see ‘stills’ of the world
Salzman and Newsome 1994
did experiments on rhesus monkeys and looked at direction of perceieved motion
Salzman and Newsome 1994 set up
iv= activit from V5 cells to different directions
dv= manipulation of the electrically stimualted cells
Salzman and Newsome 1994 results
monkeys overrpoerted seeing motions in cells in preferred direction
human and v5 exerpiments
place participants in fMRI scanner and see how V5 responds differently to moving stimuli
motion after affect illustion
after your v5 fires after a moving image to look at a still image illusion= you might still perceive motion as relative activity in pairs of neurons still firing due to prolong stimulation of one neuron that decreases the response of the other
how is perceived motion determined
by relative activity in the pairs of neurons in v5 turned in oppostite directions
stationary objecst and v5 neurons
opposing pairs of neurons are balanced (fire equally)
downard motion and v5 neurons
cells corresponding to UP dont fire and to down fire a lot
stationary objects after v5 neurons
down neurons firing a little due to prolonged stimulation adapation= results in an unbalanced respones of neuron detections= perception of V5 affected
what does V4 do
shape, colour, curvature, orientation
what does the inferotemporal cortex do
responds to COMPLEX objects and faces
neurons have ‘shape preferences’ according to macaque studies
fMRI studies and V4
faceselectivity area= object represenation
found that localized brain areas for faces and chairs in a study
visual prosopagnosia
face selectivity/recognition disorder
objects still recognized
where is visual prosopagnosia damage
right fusiform gyrus
face seelectivity
differentaiton between faces + objects
face selectivity studies
electrode implants stimuations cause faces to metaphormpizes in front of patients
fmri show activiy in frusiform face area to faces
face-specificity studies hypothesis
- domain specify
2. expertise hypothesis
domain specitify hypothesis
facial recognition is INDEPDENTN from object recognition since birth
expertise hypothesis
general object processing mechanisms in brain become ‘fine tuned’ to faces due to experience
face-specific inverstion effect
its harder to remember upside down faces
features
dog breeders study (diamond-carey 1986)
supports expert hypothesis; demonstrates inverstion effects
experts (dog trainres); stronger inverstion effect to upside down images of dogs than novices
holistic processing of upright faces
WHOLE greater than the SUM of PARTS
we dont look at individual faces but WHOLE faces
studies how its easier to recognise a face with just HALF than a HALF + FALSE half (composite effect)
how are inverted faces processed
not holistically= no composite effect
inversion effect
The face inversion effect is a phenomenon where identifying inverted (upside-down) faces compared to upright faces is much more difficult than doing the same for non-facial objects.
the face inversion effect requires an underlying face-specific mechanism to produce it
other race studies and signifiance
rhodes; looked at how european caucaisans and chinse faces had the inverstion effect with each other
demosntrates europeans better at recognizing european faces than chinese and vice vera
no inversion effect in a chinese face but yes inversion effect in a european face
supports idea of experience and holistic prorcessin (expert effect)
where vs what theory
dorsal sptream for visual spatial perception
ventral stream for visual patttern recognition
control of behaviour vs conscious perception theory
dorsal stream for visually guided behavior
ventral stream for conscious visual perception
critiques of vision for action/perception
Perception—> conscious experience of seeing
but need to also include ‘unconscious/preconscuious’
- represents visual experience of world but not the foundation for action
- it influences action but has adaptive value as link between perception and action is indirect/flexible as memory/planning play a role
patients with spatial neglect
information is presented to the unattended side of the visual field that still influences cognitive tasks.
action planning
by the ventral stream (provides visual information to enable identification of a goal object and OTHER cognitive systems plan the action to pick up that cup)
vision for action
orsal stream: use current information (visual) about the size/shape/disposition of an object to program and control the skilled movement to carry out action
allocentric perception task
Patient D.F. was asked to make a verbal judgment as to which of two stimuli was closer to a reference point located between them.
The ‘egocentric perception’ task.
Here patient DF was asked to make a similar judgement, but this time her forefinger was located at the reference point.
The ‘allocentric motor’ task
in which the patient was asked to make a pointing response from an arbitrary start point to mime the location of the test stimulus with respect to the reference point
) The ‘egocentric motor’ task
in which the patient was asked to make a direct pointing response from a start location to a target stimulus
