Object recognition with reading Flashcards
Gestalt approach
Centred on structuralism. Wertheimer, Koffka, Kohla were founding Gestalt psychologists. The Whole Is Different Than The Sum Of Its Parts
Gestalt rules
Pragnanz, Of several geometrically possible organization that one will actually occur which possesses the best, simplest and most stable shape, similarity, good continuation, proximity, common fate, meaningfulness or familiarity
Modern Gestalt principles, Palmer (1999, 1992) and Palmer & Rock (1994):
common region, connectedness and synchrony.
Palmer and Beck 2000
using the repetition discrimination task that grouping effects how something looks and the speed we can process it at. Subjects were asked to look at images and press a button when two circles were next to each other or press a different button when it was two squares. When the two items were within the same group the reaction time was significantly quicker.
Figure ground segregation
Important step in recognition of object. The figure is more thing like and memorable, the figure is seen as in front of the ground, the ground is seen as unformed and extends behind the figure and the contour separating the ground and figure seems to belong to the figure. Symmetrical objects are often seen as figures
Limitations of gestalt
more descriptions. in some cases, difficult to say what constitutes the “simplest” or “best” form or how “good continuation” should be defined. good starting point though.
Triesman 1987, 1993, 1998
Feature integration theory
Steps in FIT
identify primitives (preattentive), combine primitives (attentive), perceive object, compare to memory and recognise object
Primitives
Curvature, Tilt, Colour, Line crossings, Line ends, Movement, Closed areas, Contrast, and Brightness. During visual search if the efficiency of this search is independent of the number of items presented, this is called popout. These are primitives.
Boundaries in FIT
if you have 2 regions containing different primitives a boundary will appear
Illusory conjunction
When a stimulus possesses two primitive features, they are sometimes combined inappropriately
Role of attention in FIT
Attention binds features together into objects
FIT main components and restrictions
Concerned with early feature extraction and processing. Highlights the role of attention but can only account for basic features
Biederman
Recognition by components
RBC basics
36 geons, invariant and discriminable from almost all viewpoints. ‘non-accidental properties’. Resistant to visual noise
RBC steps
edge extraction, parse image into regions of concavity and detect non-accidental properties, determination of components, match components to object recognition. when geons can be determined object can be recognised
principle of componential recovery (goldstein 2010)
if we can recognise an object from its geons
Biederman 1987
Removal of contours defining concavities affects object recognition
Biederman & Cooper, 1991
Priming of contour-deleted images. Visual priming seen if same geons are intact but only semantic priming seen otherwise
RBC problems
Doesn’t distinguish between different types of the same object. No direct evidence for geons, only evidence of a representation of that sort. Also neurons can distinguish between much smaller differences than geons. RBC may need to be refined to show how we distinguish between, for example, faces, that have the same features but look different (goldstein 2010)
Perrett and Oram, 1993
based on geons we cannot distinguish between two different finches
Marr theory and steps
computational approach: image, primal sketch (find contours), 2.5D sketch viewer centered, 3D model description (object centered), (find axes) object catalogue.
Marr Finding contours
identify sharp changes in contrast (not shadowns). Zero-crossings. Second derivative. Find when the rate of change of the rate of change is 0. Simple cells perform this as edge-detectors
Zero-crossings and 2.5D image
Images can be combined from a course to a fine scale to get a raw spatial sketch. Gestalt principles used to define where you have blobs, bars, edges and features. 2.5D
