Unit 9 Flashcards
How do we perceive depth?
by using information from:
- the environment
- physical sensations
What is one of the most widely known approaches to the question as to how we perceive 2d images as 3d?
The cue approach
What is the cue approach?
study of information in retinal image that provides cues regarding depth
What are the three main types of visual cues?
Oculomotor
Monocular
Binocular
Oculomotor cues
information we can feel because of eye movements:
- convergence
- accommodation
Convergence
inward movement of eyes when looking at nearby objects
-> causes change in convergence angle
movement produces physical sensation
-> used by NS to calculate distance
Accomodation
Change in shape of lens to focus on objects at various distances
Ciliary muscles
muscles that change shape of lens
Tension caused by ciliary muscles used to calculate distance
What are oculomotor cues useful for?
Visual information of up to an arms length
What is more useful? Convergence or accomodation?
Convergence (usually), as it produces a stronger physical sensation
Monocular cues
depth information from just one eye
consist of:
Accommodation
Pictorial cues
Motion cues
Occlusion
When an object in a scene hides another one
partially obstructed object perceived as further away
-> only gives relative distance
Relative height
Objects higher in visual field generally perceived as further away
-> however depends on horizon
-> for objects above horizon opposite effect
Familiar size
Using prior knowledge of size of objects to judge distance
most useful when other information about depth isn’t available
Relative size
when we know that that two objects are of same size but presented as different size
-> located at different distances
-> objects further away will occupy less visual space
Perspective convergence
converging lines towards a point in a 2D image
-> objects closer to the point are further away
Atmospheric perspective
The further an object is away, the greater the number of dust, water and air particles between us and the object
-> if object in 2D image less sharp (often with blueish colour)
-> appears further away
Why does the blueish colour occur for far away objects?
blue light scatters off of particles easier than other colours of visible light
Texture gradient
When objects in environment are equally spaced apart
-> produce perception of texture
-> objects less spaced: further away
-> objects more spaced: closer
=> change in texture: texture gradient
Shadows
Decrease in light sensitivity because of the obstruction of light
Give information about three-dimensional shape of objects
Motion cues
monocular cues that rely on movement to perceive depth
Motion parallax
when moving by objects:
- going slower appear more distant
- going faster appear closer
Why does motion parallax occur?
images of close and distant objects move across retina at different speeds
Deletion and accretion
some objects cover others (deletion)
some objects get covered (accretion)
What does the utility of monocular cues depend on?
situation
distance
Binocular cues
take differences between images created in left and right eye into account
What is the difference in images called?
binocular disparity
What is stereoscopic depth perception?
basis: binocular disparity
easily seen in cinemas
3D movies use two different angles
-> 3d glasses help separate two images
What is the binding problem?
How do we combine individual characteristics to perceive whole object?
Feature integration theory
Treisman & Gelade
attempts to answer binding problem
-> 2 stages of object recognition
2 stages of object recognition
1 Preattentive stage (feature search): individual characteristics independently and automatically detected
2 focused attention stage(conjunction): FA used to combine individual features
How did Treisman & Schmidt find evidence to support the Feature integration theory (FIT)?
illusory conjunctions
participants shown shapes and numbers (–200ms)
needed to say numbers before shapes
-> individual feature detection not influenced
-> conjunction impaired: couldn’t correctly combine colours and features since FA was disrupted
Recognition-by-components theory
Biederman
geons (simple geometric shapes) aid in object recognition
recognition of objects by dividing them into geons
What is a fundamental assumption of the recognition-by-components theory?
viewpoint invariance
geons equally recognisable from every angle
-> also applies to objects constructed from geons
What is the issue with the recognition-by-components theory?
doesn’t explain how we recognise specific faces
should cause same neurone activation for viewpoint invariant geons but doesnt (only some in inferior temporal cortex)
What is one of the most prominent theories as to how we recognise objects
Prototype theory
we recognise objects and compare them with object that best represents category
-> prototype
What is a prototype?
averaged model of all previously encountered objects for a categroy
What is typicality?
the degree to which variations represent the prototype
-> high typicality = high similarity with prototype
How did Rosch quantify typicality?
showed participants series of photos
had to rank from 1-7 which photo best represented the category
How did Rosch & Mervis demonstrate typicality?
had to name characteristics of multiple objects
-> different objects of a category show high family resemblance
=> link between typicality and family resemblance
How do we organise categories of objects to take into account more specific differences in characteristics between objects?
organising them into hierarchical structures
The three levels in hierarchy of object recognition
Global (Superordinate)
Basic
Specific
Which is the most psychologically important?
The basic level
->majority of people use it to rapidly recognise an object
How did Rosch et al. prove the preference for the basic level using family resemblance?
list features of:
- furniture -> 3 features
- table -> 9 features
- kitchen table -> 10.3 features
=> demonstrates usefulness of basic level
What else shows the more useful nature if the basic over the specific level?
Two objects of the basic level have less similarities that two objects at specific level
What does the basic level depend on?
experience
