Outline 10/22/98

Sensation

3 Common Principles (cont.)

Interaction

Interaction in Time: Adaptation

Interaction in Space: Contrast

Perception

The fundamental question

Gestalt Psy. and the laws of Pragnanz

Perceptual Constancy

Across movement, shape, & size

Visual Illusions & Depth Percepetion

 

Why does color afterimage work? Adaptation and "Opponent Processes"

Every hue (i.e., color) has a complementary hue. When mixed together, these two hues form gray.

Two pairs are crucial--blue/yellow and red/green.

Why? Because they are antagonists--meaning that when they are balanced, we perceive gray.

 

 

Interaction is Space: Contrast

In vision, the response in one receptor region depends upon how neighboring receptor regions are responding.

 

 

Brightness Contrast

 

Color Contrast--the Chromatic counterpart to brightness contrast.

 

 

From Sensation to Perception Color vs. Movement Afterimage

 

Color Afterimage--Retinal Processing

 

 

Motion Afterimage--Cortical Processing

 

The Fundamental Question of Perception

 

How do we move from bits and pieces of sensation to perceptual wholes?

 

 

Gestalt Psychology

Gestalt is a German word for "whole"--applied to this perspective because of belief that whole is greater than sum of the parts.

 

 

Laws of Pragnanz = Laws of organization.

 

 

Proximity

Contnuation

Closure

Similarity

Symmetry

Figure Ground

 

 

Perceptual Constancy

Sensations (i.e., the data) change, but perceptions remain the same. Three examples:

With head movement

 

Shape constancy

 

Size constancy

 

 

Perceptual Illusions: Experience Gone Awry

 

 

Depth Perception: The Müller-Lyer Illusion

 

 

Retinal Size and Depth Perception

Color Afterimage One More Time!

 

 

For the moon illusion remember:

Retinal size is constant.

Apparent size changes as a function of perceived distance (i.e., depth cues).

On the horizon, depth cues suggest the moon is further away than when the moon is high in the sky.

If retinal size is constant, but depth cues suggest further away, brain concludes the moon must be bigger.