Pattern Recognition

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I. Gestalt Psychology and the Principles of Organization

proximity--bias to group together visual features that happen to be close to one another

similarity--bias to perceive similar features to group them together; surfaces of one object have similar visual textures

good continuation--bias to perceive smooth continuous lines over sharp discontinuities

closure--bias to perceive the world as closed figures; allows us to perceive whole objects even if parts are blocked from view

seem to be a good description of how we perceive things

Ex.: subjects were given a figure and then shown parts of it and asked if they were subparts of the original figure; people had trouble recognizing the subparts that did not follow the Gestalt principles

II. Theories of Visual Pattern Recognition (object recognition)

A. Template matching--similar to pictures

input from retina --> patterns of light and dark --> patterns are conveyed to visual parts of the brain where they are compared to large libraries of templates --> find 1/1 match --> retrieve verbal information from memory about the stimulus

what happens if the input is altered slightly? we can still recognize objects, this is a problem for template matching; argues that we have so many templates that we can still recognize them or that input is normalized (cleaned up) when it comes in

Problem--different handwriting

B. Feature Analysis

recognizes different parts of the object

many systems that each process one specific thing

Two steps: 1) extraction of a bunch of features 2) recognizing the combination of features

physiological evidence--primary visual cortex is full of neurons geared towards feature detection; sets of cells that identify a single feature

behavioral evidence--when people misidentify a letter/object, it is usually because they misidentify a single feature (e.g. C --> G)

C. Recognition-by-components (Geon Theory)

type of feature analysis; proposes a series of geometric features as building blocks