Last week...• why object recognition is difficult,

• the template model

• the feature recognition model,

• word recognition as a case study

Today...

• Recognition of 3-d objects

• Recognition of faces

• Attention

Object Recognition

How are 3-dimensional objects

recognized?

Feature Theory: problems

Relationships between features:

= 1 line1 half-circle

These 3 letters share the same set of features… how are they distinguished by the visual system?

A theory is needed that consider the spatial relationshipsbetween the features of an object...

Recognition-by-Components

Irv Biederman

Recognition-by-Components

• 36 Geons (Geometric Ions)

Non-Accidental Features

Visual features that are evident regardless of the observer’s viewpoint.

• Each geon has non-accidental features:

– features that you can always see b/c they don’t change in different orientations

– co-terminating lines can be seen to coterminate regardless of where the observer is.

– straight lines always look straight

RBC: Matching process

1 - detect elementary features, edges

2 - find non-accidental properties

3 - determine component geons and their spatial relationships

4 - match to memory

RBC: evidence

Partial or Degraded objects

Object complexity

Unusual orientations

RBC: evidence

Partial or Degraded objects

Object complexity

Unusual orientations

RBC: evidence

Partial or Degraded objects

Object complexity

Unusual orientations

RBC: problems

• Similar objects

RBC: problems

• Similar objects…

• faces, animals and other natural objects are hard to specify with geons

• RBC is pretty much a bottom-up model of object recognition. Top-down effects have not yet been addressed.

• View-point independent

A possibility:

Maybe there are multiple types of objects recognition, and RBC is good for one of them.

That is, perhaps models like RBC are good for pattern recognition cases where simple features are extracted and structural models are constructed from those features.

Another type of object recognition might involve a more holistic or configural coding of object features. This system would be important for situations where objects were not easily broken down into individual features.

Examples of this kind of object: faces, animals...