Chapter 8: Perceiving Motion

Question 1

What are the 3 functions of movement perception?

Answer 1

1. Understanding events: movement of objects assist in organization of stimuli
2. Attracting attention: important for survival if predator
3. Information about objects: ambiguous objects could be misinterpreted without movement of objects or observer

Question 2

What is Akinetopsia?

Answer 2

Motion agnosia; damage to cortex resulting in an inability to perceive movement

Question 3

What is Attentional Capture?

Answer 3

Motion attracts attention to the moving object

Question 4

What are 4 ways to perceive motion?

Answer 4

1. Real motion
2. Illusionary motion: basis of movement in movies
   - ex, apparent motion
3. Induced motion: movement of one object causes perceived movement of another
   - ex, moon moving behind the clouds
4. Motion Aftereffect: looking at a moving stimulus 30-60secs then stationary object looked at will be perceived to be moving in opposite direction
   - ex, waterfall

Question 5

Explain Larson’s experiment involving real vs apparent motion

Answer 5

3 conditions:

1. Control condition: 2 dots flashing simultaneously
2. Real motion: 1 dot moving
3. Apparent motion: 2 dots flashed to appear as if moving
   - Result: (1) activated separate areas of visual cortex
   - Result: (2) and (3) activated similar areas
   - Finding: perception of motion is related to the same brain mechanisms

Question 6

What are the 3 conditions of motion perception?

Answer 6

1. Object moves, observer is stationary: creates moving image on retina
2. Object moves, observer’s eyes follow: stationary image on the retina
3. Observer moves through stationary environment: moving image on retina but environment is perceived as stationary

Question 7

What are the 2 explanations for motion perception?

Answer 7

1. Ecological approach: info is available in the environment for perception
2. Physiological approach: neural processing

Question 8

Define Local Disturbances

Answer 8

Disruptions in the optic array by covering/uncovering the background in part

Question 9

Define Global Optic Flow

Answer 9

Overall movement of optic array indicating that an observer is moving, not the environment

Question 10

What is the Reichardt Detector?

Answer 10

A neural network that encodes motion

When receptors are stimulated right to left, neuron fires

Question 11

Explain the Corollary Discharge Theory

Answer 11

Movement perception depends on 3 things:

1. Motor signal (MS): signal sent to move eye muscles
2. Corollary discharge signal (CDS): split of an MS
3. Image displacement signal (IDS): movement of image stimulating receptors across the retina

• Movement is perceived when Comparator receives input from either CDS or IDS BUT NOT BOTH
  (Explains why environment perceived as stationary when observer moves through stationary environment)

Question 12

What are 2 pieces of evidence that support the corollary discharge theory?

Answer 12

• Damage to MST leads to perception of movement of stationary environment
• Patient R.W.: damaged MST, IDS was created by eye movements
• Real-Movement Neurons: in monkeys, respond only when a stimulus moves and not when eyes move