Object Perception. Perceptual Grouping and Gestalt Laws. Law of Similarity. Items that look similar will be perceived as being part of the same form. Law of Good continuation. This is perceived as a square and triangle, not as a combination of strange shapes.
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Law of Similarity.Items that look similar will be perceived as being part of the same form
Law of Good continuation.This is perceived as a square and triangle, not as a combination of strange shapes
Law of Proximity.Items that look are nearby are grouped together
Johannson point light displays
From: Emily Grossman
Collection of point light displays: http://astro.temple.edu/~tshipley/mocap/dotMovie.html
Figure 3D from Geisler et al. (2001) paper
Psychophysical experiment: detect which image contains a winding contour:
Performance could be predicted by assuming observers uses the statistics of the natural world
Detect patterns by matching visual input with a set of templates – see if any template matches.
What about invariance to translation, scaling and rotation? Solution: Find template that best aligns to image (using translation, rotation, scaling)
Problem: template matching is not powerful enough for general object recognition
1) pixel-based (light intensity)
2) primal sketch (discontinuities in intensity)
3) 2 ½ D sketch (oriented surfaces, relative depth between surfaces)
4) 3D model (shapes, spatial relationships, volumes)
The hierarchical organisation of the human figure (from Marr & Nishihara, 1978) at various levels: (a) axis of the whole body; (b) axes at the level of arms, legs, and head; (c) arm divided into upper and lower arm; (d) a lower arm with separate hand; and (e) the palm and fingers of a hand.
except for a few “accidental” views:
Biederman (1987). Participants were presented with degraded line drawings of objects. Recognition was much harder to achieve when parts of the contour were omitted than when other parts of the contour were deleted. This confirms the assumption that information about concavities is important for object recognition.
Examples of “Greebles”. In the top row, four different “families” are represented. For each family, two members of different “genders” are shown (e.g., Ribu is one gender and Pila is the other). The bottom row shows a new set of Greeble figures constructed on the same logic but asymmetrical in structure.
Speed of Greeble matching as a function of stage training and difference in orientation between successive Greeble stimuli. Based on data in Gauthier and Tarr (2002).
Non-matching stimuli in same-different task
invariance condition: features are slighty rotated. This results in view-invariant features
rotation condition: using mirror images. requires mental rotation and viewpoint dependent processes
Speed of performance in (a) the invariance condition and (b) the rotation condition as a function of angular difference and trial type (matching vs. non-matching). Based on data in Vanrie et al. (2002).
Later identification of objects is more accurate when object is embedded in coherent context
Deficits in Object Recognition
Patients can not distinguish
between objects, despite clear
differences in color and shape.
Riddoch and Humphreys (2001).A hierarchical model of object recognition and naming, specifying different component processes which, when impaired, can producevarieties of apperceptive and associative agnosia.