Higher Visual Processing

Visual Cortex (area V1(& V2)):

Hubel and Wiesel (1959)

 

Types of Cortical Cells:

1. Simple Cortical Cells:

 

 

 

•  

 

 

e.g.

 

 

 

 

2. Complex Cortical Cells:

 

 

e.g.

 

 

 

 

 

 

3. End-Stopped Cells: (a.k.a. feature detectors)

 

 

e.g.

 

 

 

 

 

 

Organization of Cortical Cells:

 

 

 

1. Location Columns:

 

 

 

 

 

 

 

2. Orientation Columns:

 

 

 

 

 

 

3. Ocular Dominance Columns:

 

 

 

 

 

4. Hypercolumns -

 

Extrastriate Cortex (areas beyond the primary visual cortex(V1) -- V3, V4, & V5)

Different processing pathways for different pieces of information.

A. Form channel (V3):

•  

 

 

•  

 

 

 

• visual form agnosia:

 

 

e.g.

e.g. prosopagnosia--

 

 

B. Color channel (V4):

 

•  

 

 

• stroke patients

 

 

 

C. Motion channel (V5):

•  

 

 

 

•  

 

 

 

•  

 

 

 

 

 

Object Perception

Gestalt Approach to Object Perception: (gestalt means "whole" or "shape")

• "The whole is different than the sum of its parts."

Figure and Ground:

 

e.g. ball resting on a grassy field

ball =

grass =

 

e.g.

 

 

•  

 

Factors that determine what is seen as figure and ground:

 

•  

 

 

Oyama (1960) -

 

= same size= smaller size

 

 

 

 

 

 

Examples of Ambiguous Figure/Ground:

e.g. Escher

 

 

 

 

Illusory Contours:

e.g.

 

More complex illusory contours -

 

 

 

 

 

 

• contours can vanish due to how we interpret the visual stimlulus (top down processing)

 

e.g. necker cube figure

 

 

 

Gestalt Principles of Organization:

 

 

1. Proximity:

 

 

 

 

2. Similarity:

 

3. Good Continuation:

 

 

4. Common Fate: (Law of common motion)

 

 

5. Closure:

 

 

6. Pragnanz:

 

 

 

 

 

 

 

Modern Gestalt Principles:

7. Common Regions:

 

 

8. Element Connectedness:

 

 

9. Synchrony:

 

e.g. flashes of light

• Visual System Wants to Organize Visual Scene