Chapter 5: Perceiving Objects and Scenes. Figure 5-3 p97. Why Is It So Difficult to Design a Perceiving Machine?. The stimulus on the receptors is ambiguous. Inverse projection problem: An image on the retina can be caused by an infinite number of objects. Objects can be hidden or blurred.
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Why Is It So Difficult to Design a Perceiving Machine? • The stimulus on the receptors is ambiguous. • Inverse projection problem: An image on the retina can be caused by an infinite number of objects. • Objects can be hidden or blurred. • Occlusions are common in the environment.
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Why Is It So Difficult to Design a Perceiving Machine? - continued • Objects can be hidden or blurred
Why Is It So Difficult to Design a Perceiving Machine? - continued • Objects look different from different viewpoints • Viewpoint invariance: the ability to recognize an object regardless of the viewpoint • This is a difficult task for computers to perform
Perceptual Organization • Approach established by Wundt (late 1800s) • States that perceptions are created by combining elements called sensations • Structuralism could not explain apparent movement • Stimulated the founding of Gestalt psychology in the 1920s by Wertheimer, Koffka, and Kohler • The whole differs from the sum of its parts. • Perception is not built up from sensations, but is a result of perceptual organization.
Perceptual Organization - continued • Illusory contours- contours that appear real but have no physical edge
Gestalt Organizing Principles • Principles of perceptual organization. • Good continuation - connected points resulting in straight or smooth curves belong together • Lines are seen as following the smoothest path • Pragnanz - every stimulus is seen as simply as possible • Similarity - similar things are grouped together
Gestalt Organizing Principles - continued • Proximity - things that are near to each other are grouped together • Common fate - things moving in same direction are grouped together • Common region - elements in the same region tend to be grouped together • Uniform connectedness - connected region of visual properties are perceived as single unit
Perceptual Segregation • Figure-ground segregation - determining what part of environment is the figure so that it “stands out” from the background • Properties of figure and ground • The figure is more “thinglike” and more memorable than ground. • The figure is seen in front of the ground. • The ground is more uniform and extends behind figure. • The contour separating figure from ground belongs to the figure (border ownership).
Perceptual Segregation - continued • Factors that determine which area is figure: • Elements located in the lower part of displays • Convex side of borders
Subjective Factors That Determine Which are is Figure • Gestalt psychologists believed that experience and meaning play a minor role in perceptual organization. • Gibson Experiment showed that figure-ground can affected by meaningfulness of a stimulus.
Perceiving Scenes and Objects in Scenes • A scene contains: • background elements. • objects organized in meaningful ways with each other and the background. • Difference between objects and scenes • A scene is acted within • An object is acted upon
Perceiving Scenes and Objects in Scenes - continued • Research on perceiving gists of scenes • Potter showed that people can do this when a picture is only presented for 1/4 second • Fei-Fei used masking to show that the overall gist is perceived first followed by details.
Perceiving Scenes and Objects in Scenes - continued • Global image features of scenes • Degree of naturalness • Degree of openness • Degree of roughness • Degree of expansion • Color • Such features are holistic and perceived rapidly
Regularities in the Environment: Information for Perceiving • Physical regularities - regularly occurring physical properties • Oblique effect - people perceive horizontals and vertical more easily than other orientations • Uniform connectedness - objects are defined by areas of the same color or texture
Regularities in the Environment: Information for Perceiving – continued • Physical regularities - regularly occurring physical properties • Homogenous colors and nearby objects have different colors • Light-from-above heuristic - light in natural environment comes from above us
Regularities in the Environment: Information for Perceiving - continued • Palmer experiment • Observers saw a context scene flashed briefly, followed by a target picture. • Results showed that: • Targets congruent with the context were identified 80% of the time . • Targets that were incongruent were only identified 40% of the time.