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