lecture 5 Flashcards
what is the importance of form and oragnisation?
environment contains hundreds of overlapping objects yet perceptual experience is:
- structured
- made of coherent objects that we can recognise, use and usually name
how does the distal image differ from the proximal image?
the image is inverted, tiny and flat
why is the proximal stimulus inverted, distorted, tiny and flat?
to compensate for eye movement, body movement and object movement
features of the retina that must be taken into consideration
the retina is curved
it is constantly moving
how often does the retina move
up to 50 times a second
what is marr’s approach concerned with?
representation of edged, contours and other areas of contrast chang e
is marr’s approach bottom up or top down? how so?
bottom up
starts off with retinal input into perceptual system in form of retinal image and describes in stages of processing this image
what type of model is marrs approach?
computational model
what do you need to consider in computational theory?
what is the model trying to do? what are the processes for? what is the goal?
what needs to be considered on the algorithmic level of a computational model ?
what algorithm is needed? what process?
what needs to be considered on the mechanism level of computational model?
what mechanism is needed to implement the algorithm? eg. neural/ biological system
importance of computational models?
algorithmic system is more likely to be understood by understanding the problem than explaining the mechanism in which it is embedded
(trying to understand perception by studying neurons is like trying to understand a bird in flight by studying only feathers)
5 stages of retinal image analysis (Marr’s approach)
1) retinal image
2) grey level description
3) primal sketch
4) 2 1/2 D sketch
5) 3D representation
grey level description
measuring the intensity of light at each point in the image
primal sketch
-representation of contrast change over a range of spatial frequencies (blobs, edges, bars..)
2 1/2 D sketch
representation of orientation, depth and colour relative to the observer
primal sketch combined with depth cues, colour, motion
not 3D because it is observer oriented
3D representation
representation of objects independent of the observer
2 1/2 D sketch analysed for 3D volume primitives
produces a 3D representation that is independent from the observer
what stage of Marr’s approach is teh conscious experience of vision
3D representation
what is the Gestalt approach concerned with
rules of perceptual organisation
that we dont see in lines and figures but in forms and shapes
what did Gestalt believe?
the whole is greater (different) than the sum of its parts
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)
is the Gestalt approach top down or bottom up?
top down
what is insight learning?
sudden realisation of the solution to a problem
in the absence of trial and error-minimising teh gap between current state and goal
what is important in insight learning?
you have to see the problem as a whole
what is special about insight learning?
it is thought to be a uniquely human trait/ skill
argument supporting the Gestalt approach
ambiguity does not arise in the real world, we see a stable and organised world. therefore we must have perceptual organisation
argument: we see objects according to all their elements taken together as a whole
what are principles of perception?
seemingly innate laws that determine the ways in which objects are perceived
what did gestalt psychologist seek to do?
isolate the principles of perception
what are the gestalt laws of perceptual organisation?
1) similarity
2) good continuation
3) proximity
4) connectedness
5) closure
6) common fate
7) familiarity
8) invariance
9) pragnanz: good figure
similarity
things that appear to be grouped together
what can similarity occur due to?
shape, lightness, hue, orientation, size
good continuation
points that, when connected, result in a straight or smoothly curved lines are seen as belonging together
lines tend to be seen in a way as to follow the smoothest path
proximity
things that are near one another appear to be grouped together
connectedness
things that are physically connected are seen as a unit
closure
of several geometrically possible perceptual organisations, a closed figure will be preferred to an open figure
why do we tend to complete a broken figure?
because of the strong closure cue for organising what we see
common fate
things that are moving in the same direction are grouped together
objects with the same orientation are grouped together
familiarity
things are more likely to form groups if the group feels more familiar or meaningful
invariance
simple geometrical shapes are recognisable independent of rotation, translation and scale
captcha test? what does it rely on?
completely automated public Turing test to tell humans apart from computers
relies on humans ability to perceptually organise images by invariance, and a computers lack of ability to do so
what is the central law of gestalt psychology?
pragnanz
pragnanz
of several geometrically possible organisations, one will occur that possesses the best, simplest and most stable shape
properties that affect whether the area is seen as figure or ground
symmetry convexity area orientation meaning/ importance
symmetry in figure-ground segregation
symmetrical areas are usually figures
convexity figure-ground segregation
convex shapes usually figures
area in figure-ground segregation
stimuli with comparatively smaller area usually the figure
orientation in figure-ground segregation
vertical and horizontal orientations are usually figures
meaning/ importance in figure-ground segregation? importance?
meaningful objects more likely to be seen as figures
infers top down process
problems with the Gestalt approach?
1) underplays parallel processing and unconscious processing that the brain does
2) explanation of how some of their laws worked was wrong
3) laws provide a description rather than an explanation
4) laws ill defined (e.g. what is the simplest and most stable shape?)
5) stating the obvious?
positives of the Gestalt approach
their laws appear to pe generally correct
1) percepts can be analysed into basic elements
2) the whole is greater than the sum of its parts
3) context and experience influence perception
David Marr dates
1945- 1980
published 1982
Wolfgang Kohler
1887-1967
series of experiments in Kohler and Koffka by Wertheimer
together they developed the Gestalt school
series of influential publications (1920s)
