Sensation And Perception 2 Flashcards
Feature analysis determines
What an object is
Feature analysis determines what an object is, the features can guide
Our perception and take cues from it
Preliminary stage is where
We perceive the whole object and then the features of the object help guide our perception
The gestalt principles of organisation state that
Objects are perceived as whole units and then focus on and can be anticipated even when some of its pars are missing/incomplete and they hoped to explain why we group visual elements together
What are the five gestalt principles?
Similarity-visual elements that are similar
Proximity-the closer visual elements are
Good continuation-a logical flow
Closure-an extreme example of good continuation as we like to close gaps
Simplicity-we like simple forms
To organise the input the perceived has to
Analyse the visual scene and gestalt psychologist would argue this is just as important as the input
The information we need doesn’t come from the stimulus but from the
Perceiver
Feature net model that can identify words
Bottom up/data driven aspect-feature detectors
Top down/knowledge and experience based aspect
What is bottom up/data driven aspect-feature detectors
These would respond to basic stimuli (such as curves and lines) which would send information to more complex detectors that respond to combinations of features and send input to letter detectors which respond to letters of the alphabet and would pass the input into word detectors which would respond to whole words
What is the top down/ knowledge and experience based aspect?
Once a word is read we come up with concepts related to that word (be appropriate for the hypothesis) and the related words would be activated and this would lead to activation of the constituent letters
There is neural process which underlies this perceptual process that was started by
Wiesel and Habel
We have specialised subsystems in the
Visual system
2 main systems are
Magnocellar system and the parvocellular system
What is the magnocellular system?
Cells give rise to our perception of depth and motion (where/dorsal system carries information from the visual areas/occipital cortex to the parietal cortex)
What is the parvocellular system?
Gives rise to our perception of colour,pattern and form (what/ventral system as it is responsible for identifying what an objects is where information is carried from the visual areas/occipital cortex to the inferotemporal cortex)
The analysis of form, colour and motion occur in
Tandem as it is most efficient and different analysis can affect other analysis (this provides the biological basis for bottom up and top down information)
There is no definitive answer as to how theses systems communicate
One theory suggests that of groups of neurons are firing at the same time and pace then
It is assumed that they are working on the same object
There is no simple linear process in visual perception and there is
Communication between all regions
Damage to the magnocellular system or parvocellular system
Visual agnosia
Thrombosis/acyanopsia
Prosopagnosia
What is visual agnosia
Damage to both halves of the inferotemporal cortex so she struggles to identify objects but has normal visual acuity and could draw named objects and can walk around normally and avoid obstacles and follow objects with her eyes
What is thrombosis/acyanopsia?
Damage to area v5 so she struggles to perceive the motion of an object (sees things as a series of jerky still images)
What is Prosopagnosia?
Struggles to recognise faces but be able to identify when an object is a face and determine when they are being presented with the same face
What is shape constancy?
The stimuli we recieve change e.g as an object moves it creates a different retinal image depending on the viewing angle
The size of an object can vary depending on the viewing distance
This is known as size constancy but we use textual clues (the background) as well as the subject to gage the actual size of the subject but we can achieve size constancy without background clues
What Helmholtz suggested was that we make use of the relationship between
Retinal image size and distance to make unconscious inferences (calculations)
In relation to Helmholtz theory: I.e if you double the distance between an object and the observer you
Half the retinal image and if you triple the distance between the object and the observer the retinal image is a third of the size
The retinal image is
Ambiguous and static (does not capture motion)
So the same object can give rise to
Different retinal images depending on the viewing angle and two different objects can produce a similar retinal image
The brain uses cues
In order to construct a 3D perception of the world
How many occulomotor cues are there
2
Occulomotor cues: the brain has access to proceptive information
An awareness of movement in the body and the effort that is required for that movement
Oculomotor cues: when we focus on an object that is close to us, two thing happen:
We get accommodation and convergence which indicates to the brain how close an object is
What is accommodation
A change in shape of lens, which has to bulge out to get a clear image of an object close to the perciever
What is convergence
When we are focusing on an object which is close the eyes turn inward
Binocular cues:
Effective when both eyes are used and there is no movement in the object
Binocular cues: our eyes pick up slightly different retinal images and this can provide
A cure for depth by providing us stereoscopic depth/stereopsis
What is stereoscopic depth/stereopsis
We’re two images from each eye are combined by the brain
What is it called when our eyes pick up slightly different retinal images
Retinal disparity
Who discovered stereopsis?
Charles wheetstone
How did Charles wheetstone discover stereopsis?
By presenting two images (one to the right eye and one to the left) that was very similar but displaced horizontally to artificially induce stereopsis so the observer fuses these images together and they will perceive depth
Stereopsis is not the only kind of depth perception as
Someone with one eye can still have depth perception, except in artificial circumstances
Monocular static cues are
Effective with only one eye and is only effective if there is no movement in the object and referred to as pictorial depth cues
Monocular static cues have a relative size
Larger than retinal image the closer to the perciever it appears
Monocular cues have a relative height
Objects which are closer to the horizon are higher in the visual field
The process of monocular cues is linked to experience as
Through time we learn what the average size of an object is and allows us to judge the distance of objects relative to the retinal image size of the objects
Occlusion (interposition) is
One of the most powerful depth cues as when an object is covered it’s perceived to be further away
Linear perspective refers to the fact that
As parallel lines move further away they appear to converge until they reach a vanishing point
The more things converge
The further away they appear
Texture gradients occur when
A texture is viewed from a slant rather than from directly above e.g patterns appear denser and less detailed the further into the distance they appear
Monocular movement cues can be motion in
The object or the observer
In monocular movement cues,motion can
Dispel any misinterpretations
Motion parallax refers to
The apparent motion of objects based on the movement of the retinal image across the retina and comes from motion from the observer e.g objects which are close to us appear to move past is faster than objects that are far away
Light and shadow also helps is perceive
Depth as if a shadow falls below an object we expect it to be up (I.e something that is creating that shadow)
When there is motion across the retina it is caused by
A movement in the eye (which shifts the image) or a movement in the object
However, the brain can control the eye muscles and because the movement of the eye is equal and opposite to the movement of the retinal image
Any perception of motion would be suppressed by the brain- this ensures we don’t perceive motion in the object when we move our eyes
How many types of illusionary motion are there?
Two
On type of illusionary motion: if two bulbs are placed in front of an observer and have been timed so that they are switched on one after the other so that eventually
The observer views this as a movement of light from one bulb to the other and back again
Two types of illusionary motion: correspondence problem has a blue square and a red circle placed opposite each other and are timed so that
They moved 90 degrees and the colours changed I.e the circle became blue and the square became red
So observers perceived
Clockwise motion I.e a change in position and others only observes anti-clockwise motion I.e change in colour
Visual development in children, William James, in 1880, described
The perceptual world of the newborn infant as blooming, buzzing confusion because they lack relevant perceptual experience
The visual system of infants in underdeveloped which means
They have poor vision and this impacts on their visual experience and the maturation of their visual system continues after birth and into the toddler years and beyond
Come photoreceptors are underdeveloped and placed further apart
In infants
Come receptors in infants also don’t have the ability to capture as much
Light energy and their receptive fields are further apart so they can’t capture all the information/detail that adults can
Optic nerve myelin still is
Incomplete at birth so nerve impulses are not as efficiently conducted
The visual correct is not fully developed at birth and
Maturation occurs from the inside out so interpretation of visual information is not as effective
Adults have 6/6 or 20/20 vision but in a one year old vision is
20/25 and at six months vision is around 20/30 but at birth is around 20/600
One way of measuring perception in infants is?
Change in sucking rate- if it changes we assume the infant has perceived it
Another way of measuring perception in infants is
Tracking of a moving stimulus (usually a grating)- if infants look at something for long periods it is assumed they can perceive it
A third way of measuring perception in infants
Visual evoked potential (VEP)- electrodes are placed on the infants head and brain waves are measured
A fourth way to measure perception in infants is
Preferential looking-two stimuli are presented simultaneously to see whether infants will attent more than one to another
A fifth way of measuring perception in infants is
Preferential reaching- if the infant reaches for the target object we assume they can perceive it
There is a debate as to whether infants are born with
A specific preference for faces
Research has been carried out where monkeys are deprived of face stimuli between 6-24 months after birth
And still were found to prefer face stimuli
Walton, bower and bower (1992) investigated face recognition in infants by taking a video of the mother and placed a video of a similar looking stranger side by side
And the baby could control which video could be played by sucking a dummy faster
It was found that 11 out of 12 infants sucked faster when
They saw image of their mother, showing babies prefer faces but particularly their mother’s face
Quinn, Yahr,Kuhn,Slater and Pascalis (2002) if babies have a gender preference or it was down to
Experience by looking at babies primarily cared for by women and compared them to babies primarily cared for by men
What they found was that babies who were cared for primarily by women
Preferred female faces and babies who were cared for primarily by men preferred male faces
The evidence from these experiments suggest
That there is a preference for faces but it is partly based on experience
It was found that 11 out of 12 infants sucked faster when
They saw image of their mother, showing babies prefer faces but particularly their mother’s face
Quinn, Yahr,Kuhn,Slater and Pascalis (2002) if babies have a gender preference or it was down to
Experience by looking at babies primarily cared for by women and compared them to babies primarily cared for by men
What they found was that babies who were cared for primarily by women
Preferred female faces and babies who were cared for primarily by men preferred male faces
The evidence from these experiments suggest
That there is a preference for faces but it is partly based on experience
Johnson, DZiurawiec, Ellis and Morton (1991) showed infants face-like (had the eyes,nose and mouth in the right place) and non-face like (had all the elements of a face but it was in the wrong configuration) and blank “paddles”
And measured how much infants followed these by moving their eyes and head
Infants preferred the face-like paddle over the other two and
Infants found found to show a preference for face-like stimuli as early as 5 days old, but there was still a response to the non-face like paddle that does not appear in older children
Turati, Valenza, Leo and simion (2005) found that in the same experiment 3 month old children were
More advanced in face processing as cortical maturation had occurred as they responded more to the face like paddle as opposed to the non face like paddle
One theory found that infants
Don’t require faces but prefer a configuration of elements I.e patterns in the upper half of the stimulus
One experiment placed a black square with white squares inside it, one had the squares in the upper half and one had squares on the lower half
And we’re simultaneously shown these pairs and infants consistently preferred stimuli with the squares on the upper half
This evidence suggests that infants are responding to configuration of elements rather than face itself
And this could lay the ground work for future specialisation as they are born with a face prototype that becomes more specialised the more experience with faces they get
Infants develop sensitivity to these cues
Appear to develop at different rates
Infants develop the kinetic depth cue first 2 months old
As they are sensitive to optical looming
What is optical looming?
The rapid expansion of the retinal image which is interpreted by adults as the rapid approach of an object
In an experiment infants were placed in a crib and dropped objects from a height to see if infants would blink in response and it was found that
Newborn infants don’t have a defensive blink but at two months infant consistently responded to optical looming
Another kinetic depth cue is
The change in texture gradients when textured surfaces in motion so we can tell when one is in front of the other
Researchers have presented infants with random dots that would have some motion in them and it was found that
Infants could reach for the apparently nearer surface by the time they were 3 and a half months old
The visual cliff (GIbson and Walk, 1960) where a glass table was placed on the floor
So the observer would see a steep drop as evidence for early development of motion and parallax, change the texture gradients and retinal disparity
They placed the babies on the side opposite the drop and had their parents stand at the other side and beckoned them over
But they would not cross the percieved drop
However, babies cannot crawl at birth and this process takes around 8 months
Which gave them around 8 months of visual experience showing this may not be innate
Animals who can walk sooner after birth (I.e kids, lambs and chicks) were tested in the same experiment
And they all showed the same pattern, therefore depth perception must be developed quickly after birth
Richard held measured infants sensitivity to binocular cues using visual objects (as in 3D movies)
And once the infants wore special glasses one image had the perception of depth and the other there would be no percieved depth
Using preferential looking they found that
Infants around 3 and a half months old preferred stimulus that had depth in it
Stereoacuity is
A measure of how good your ability is to combine retinal images which is determined by the arc sec
What is the arc sec?
Angular measurement rant is divided into degrees and each degree is divided into 60 minutes of an arc and each minute is divided into 60 seconds of arc and the smaller the angle, the better the stereoaucity
Brown, Lindsay, Satgunam and miracle (2007) found that
3 months-stereoaucity is unmeasurable because it was so poor
5 months-474 arc seconds (begins to emerge)
Adult-5 to 10 arc seconds
