Weeks 1 & 2 (Luke Jones) Flashcards
Why is the perception of form and organisation important?
- The environment contains hundreds of overlapping objects
- Yet the perceptual experience is of structured, coherent objects which we can recognise, use and instantly name
- The starting point is that light, reflected from objects reaches the eyes
- How do we then go from this perceiving to a coherent, stable, 3D object?
What are the two most common fallacys of the visual system?
The camera analogy
The homunculus (little man)
What is the distribution of receptors in the retina?
- Highly concentrated and small RF’s in the centre (fovea)
- More sparse and larger RF’s in the periphery
- There are uneven volumes of the visual cortex devoted to different visual arrays
Which side of the brain processes information from the left eye?
The contralateral- right side.
What shape is the retina and what does this mean for vision?
- The retina is curved
- Means there has to be some processing to decode the distorted image reflected here
How many times a second is the retinal information updated?
50 times
What elements does perception have to account for when visualising something?
- Uneven retinal distribution
- Curved image on the retina
- Eye movement, body movement and object movement
- Uneven cortical devotion to different parts of the visual field
- No explicit visual information from the cortex
What is Distal stimulus
The item in the world
(for example a tree)
What is the proximal stimulus?
The image on the back of the retina
What does the proximal stimulus lead to?
Perceptual experience
Why is perception important? (2)
- Is our only source of information about the world
- All other cognitive systems rely on perception
What are 4 main theories of visual perception?
- Gestalt approach
- Gibson’s ecological theory
- Marr’s Information processing theory
- The constructavist approach
How are the different theories of perception approached in different ways?
- Emphasis on Bottom-up vs Top-down processing
- The Goal of perception
- The methods to study perception
What is the primary maxim behind Gestalt psychology?
The whole is greater than the sum of its parts.
What approach does the Gestalt theory base its argument around?
- Top- down approach
- However, it acknowledges there is an aspect of bottom-up but there are elements missing in this approach when describing the visual system
What are Gestalt psychologists interested in?
How we group parts of a stimulus together and the way we separate figure from ground
- Segregation
and - Grouping
What is a necker cube and how does it explain the Gestalt approach?
- A 2D image of a cube which can be perceived in different ways by the same viewer
-This shows that sensation is not the same as perception. The fact that we can flip to different hypotheses of the cube indicates top-down information, separate from simple retinal vision
What is an issue with the Necker cube as an explanation of the Gestalt approach?
- Is an unfair representation
- This is because it is a 2D image of a 3D structure in which we can normally actively engage with in the environment.
Who are three key members of the Gestalt school?
Max Wertheimer
Kurt Koffka
Wolfgang Kohler
How does Gestalt argue against structuralism?
Argues for Reaction in the environment
Structualism ignores the relationship between stimuli and interpretation
How do we differentiate ambiguity in the environment according to Gestalt? (3)
- Through perceptual organisation
- Through Innate rules which determine ways in which objects are perceived
- Through experience and knowledge
What is an Issue with Gestalt theory claiming the ‘whole is different from the sum of its parts’?
- Suggests that when we look at a bike, we percieve the whole bike and not its elements
- Unconscious processing, however may infact take into account these elements
- We may then see objects as there elements in the unconscious
- We are only aware of the answer however
What are Gestalts laws of perceptual organisation?
- Similarity
- Good continuation
- Proximity
- Connectedness
- Closure
- Common Fate
- Familiarity
- Invariance
- Pragnanz (good figure)
What is Gestalts perceptual rule of similarity?
Similar things appear to be grouped together
What is Gestalts perceptual rule of Good continuation?
Points that, when connected, result in straight or smoohtly curving lines, are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path
What is Reifiction?
When there is more spatial information than what is actually present.
(Brain fills in missing information - think about knowing there is a chair under the desk although it is occluded)
What is Gestalts perceptual rule of proximity?
Things that are near to one another appear to be grouped together- Colour and form
What is Gestalts perceptual rule of connectedness?
Things that are physically connected are perceived as a unit
What is Gestalts perceptual rule of Closure?
Of several geometrically possible perceptual organisations, a closed fgure will be preffered to an open figure
What is Gestalts perceptual rule of common fate?
Things that are moving together in the same direction are grouped together (also orientated in the same direction)
What is Gestalts perceptual rule of familiarity?
Things are more likely to form groups if the groups appear familiar or meaningful
What is Gestalts perceptual rule of invariance?
We can recognise different orientations and distortions of the same object
What is Figure-Ground segregation and what is an illusion involved?
- Humans are good at determining what is the background and what is the foreground
- Rubin cube however provides an example where we are not so good at this
Why is Gestalt interested in figure-ground segregation
The ability to easily determine the foreground from the background indicated top-down processing
What are the 5 ways in which properties are segregated as figure or ground?
- Symmetrical areas are usually figure
- Convex shapes are usually figure
- Stimuli with comparatively smaller area are usually figure
- Vertical and horizontal orientations are usually figure
- meaningful objects are more likely to be seen as figure
What are the problems with the Gestalt approach?
- Underplay the parralel processing and unconscious processing that the brain does
- Explanation of how some of their laws worked was wrong
- Their laws provide a description of how things work rather than an explanation
- Thier laws are ill defined- Pragnanz- what is the simplest and most stable shape?
- Is he stating the obvious?
What approach is Gibson’s ecological theory based around?
Bottom-up approach
What does Gibson’s ecological theory of perception state?
- Perception is direct
- Rich information received from the environment is sufficient for perception
- Complex, cognitive processes are unnecessary
Why does Gibson not support lab studies of perception?
- A major component of vision is movement
- When studying 2D displays we remove this major component
- Therefore is not representative of the truth
What is an ambient optic array?
The information coming into the eye and reflecting on the retina, this can change due to observer movement
From one viewpoint, you have a fixed image of the world, as soon as you move, the array of which light reflects on the back of the eye changes
What is the most foundational observation of Gibson?
Perception is ACTIVE, movement of the observer provides additional stream information
What are invariants in Gibson’s ecological theory of perception?
- Unambiguous information about the environment
- Can be directly perceived
- For example:
Texture gradients
Horizon ratio
What is Horizon Ratio?
The proportion of the object above and below the horizon line is constant for objects of the same size standing on the same ground
What are texture gradients?
Changes in texture in the optic array tells us about distance, orientation and curvature of surfaces
This is the consequence of the fact that when objects recede away, their image becomes smaller on the retina
How has texture gradients been used to help pilots?
- Looking out of a plane onto a series of regular rectangluar fields
- When whe orientation changes, the array will change in a consistent way
- This gives a strong direct cue to the orientation to the ground
What is empirical support for Gibson’s ecological theory?
Participants could correctly identify objects, state their colour, identify the lighting conditions and the objecys spatial orientations just from black and white photos of object surfaces 2/3 correctly.
How does motion highlight invariance?
In a static scence, everything is invariant, so introduce motion to highlight these invariant properties
What are two types of motion?
- Object movement
- Observer movement (focus of Gibson)
What is the Motion Parallax?
Things far away move more slowly than things nearby
Speed of movement tells us about distance to an object
This is a monocular cue to depth
How do squirrels and pidgeons use motion parallax?
- Use because they don’t have much binocular overlap
- Use head bobbing to increase the motion parallax
- Will run orthogonally/ along the side to increase the motion cue
What is Optic Flow?
A combination of parallax and retinal size
For example
When a ball comes towards us the motion parallax means it gets larger on the back of the retina until it hits our face
How do self-driving cars function?
Use optic flow to detect the changing environment
How are road lines designed to use optic flow?
- Horizontal lines are painted on the road when coming to a junction
- The distance between the lines becomes progressively narrower
- This uses optic flow to fool the brain that the lines are approaching faster
- Causes us to slow down