Depth and Visual Scene Analysis Flashcards
How do we perceive depth?
monocular cues - one eye - relative hight and size
binocular cues - two eyes - disparity
Monocular cues - hight and size
Relative hight and size - objects that are below horizon and base higher = more distant. Two objects that are of equal physical size, the more distant one will take up less of our field of view - requires prior knowledge to judge distance
Monocular cue - occlusion
closer objects will occlude further away ones
Monocular cues - linear perspectives
parallel lines extending away from observer converge in distance
Monocular cues - texture gradient
texture elements get smaller and more dense with distance
foreshortening when surface becomes tilted - circles become ovals
Monocular cues - motion parallax
As we move, more distant objects glide more slowest than nearer
Monocular cues - shadows and shading
shadows and shading creates concepts of depth
What is binocular disparity
Stereoscopic vision - out two eyes receive slightly different image of the world
Disparity creates differences in image location of object seen by left and right eye
Size and direction of disparity depends on objects depth - further away = less disparity
What is a horopter? Differences between crossed and uncrossed disparities
Set of points in space that project to corresponding positions in 2 retina’s - zero disparity, involves a fixation point.
(if one retina could be slid on top of the other, the points would overlap)
When objects are closer than the horopter = have crossed disparities
when objects are further away than the horopter = uncrossed disparities
How do we perceive objects according to the structuralism view?
Pioneered by Wundt:
Proposed that object perceptions arise from a process in which primitive sensory ‘atoms’ evoke memories of other ‘atoms’ that have been associated in memories.
How do we perceive objects according to the Gestalt school of thought?
Whole form or configuration is greater than the sum of its parts
Argued against structuralism with illusory contours - some images evoke perception of edges in locations where no change in luminance.
Proposed principles by which elements in image are grouped to create larger objects.
Principles are all manifestations of the ‘Law of Pragnanz’ - ‘good figure’
Principles of Gestalt school of thought.
Proximity = things close together group together
Similarity = things similar grouped together
Common Fate = things that move together are grouped
Good continuation = group elements to form smoothly continuing lines rather than abrupt of sharp angles
Closure = group elements to form complete figures, even if incomplete (top-down knowledge)
Symmetry = more likely to group elements that are balanced or symmetrical.
Assessment of Gestalt School of thought
+ good face validity - seems that perceptual objects are not simply the sum of its parts
+ principles hold across a wide range of images
- some principles vague - not sure what is meant by ‘simple’ shape
- no coherent workable account of underlying neural mechanisms
Kohler proposed electrical field theory (lines of flow, created structure of perception in brain) - no evidence
