Form Perception Flashcards
What is Marr’s approach to visual perception concerned with?
concerned with the representation of edges, contours and other areas of contrast change
What is Gestalt’s approach to visual perception concerned with?
Rules of perceptual organisation
Give features of Marr’s approach
- ‘Bottom up’ approach
- Starts with input to perceptual system in form of retinal image and describes the stages in processing of this image
- Each stage takes as its input the information from the previous stage and transforms it into a more complex description or representation
- Computational model
What is a computational model?
- Computational theory: what is the model trying to do? What are the processes for? What is the goal?
- Algorithmic level: what algorithm is needed? What process?
- Mechanism level: What mechanism is needed to implement the algorithm – biological, neural mechanism
What are Marr’s stages in his model?
- Retinal image
- Grey level description – measuring intensity of light at each point in the image
- Primal sketch – representation of abrupt contrast change (blobs, edges, bars etc) over range of spatial frequencies
- 21/2D sketch – representation of orientation, depth, colour relative to the observer
- 3D representation – Representation of objects independent of observer (only stage we are aware of)
How is the 2 1/2 2D sketch turned into a 3D representation?
- 2 ½ sketch analysed for 3D volume primitives (cylinders, cones, etc.)
- Produced 3D representation that is independent of observer
- Uses memory experience of world
- E.g. if looking at a nose you will know that it sticks out
- Conscious experience of vision
Why is the computational approach important?
- An algorithm/ rule/ system is more likely to be understood by understanding the problem that has to be solved, rather than examining the mechanism (and hardware) in which it is embodied
- To understand perception (purely) by studying neurons is like trying to understand bird flight by studying only feathers: function not form (AI argument)
- Neurons may not only be the thing that can carry out human processes
What is Gestalt Psychology?
the whole is greater (different) than the sum of its parts (Max Wertheimer, 1912)
What is the Gestalt school?
- Max Wertheimer
- Kurt Koffka
- Wolfgang Kohler
- Series of experiment on Kohler and Koffka by Wertheimer
- Together they developed the Gestalt school
- Thought you needed to see problems as a whole
What is the Gestalt approach?
- The whole is different to the sum of its parts
- Don’t see lines and figures, but forms and shapes
- Top-down approach
What is perceptual organisation (Gestalt school)?
- Ambiguity generally does not arise in the real world. We usually see a stable and organised world
- For example, most people see a set of overlapping circles, rather than one circle touching two adjoining shapes that have ‘bites’ taken out of them. Why?
- Argue that we see objects according to their elements taken as a whole
- Sought to isolate principles of perception: seemingly innate ‘laws’ which determine ways in which objects are perceived
- The unified whole is different from the sum of the parts, e.g. a bike
What are the 8 Gestalt laws of perceptual organisation?
- Similarity
- Good continuation
- Proximity
- Connectedness
- Closure
- Common fate
- Familiarity
- Invariance
What is similarity?
- Similar things appear to be grouped together
- Grouping can occur due to shape, lightness, hue, orientation, size
What is good continuation?
- Points that, when connected, result in straight or smoothly curving lines, are seen as belonging together, and the lines tend to follow the smoothest path. (we tend to continue lines)
- Reification – more spatial info than is present
What is Reification?
When we perceive more spatial information than is present
