Chapter 8 - Perceiving motion

Question 1

1- Akinetopsia or
“motion blindness”

Answer 1

• Akinotopsia
• Motion is either very difficult or impossible to perceive.
• Very rare condition
• Traumatic brain injury
• Neurodegenerative disease such as Alzheimer’s
• Epilepsy, hallucinogen persistent perception disorder (HPPD).
• Damage to V5 medial temporal (MT) (Temporo-parieto-occipital junction (TPJ)).

L.M. patient case

Question 2

2- Importance of detecting movement:
Detecting Things

Answer 2

• Observers perceive shapes more rapidly and accurately when an object is moving.
• Movement also serves an organizing function, which groups smaller elements into larger units.
• The motion of individual birds becomes perceived as the larger unit of the flock, in
  which the birds are flying in synchrony with
  each other.
• Biological movement:
• When a person or animal moves, movement of individual units—arms, legs, and body— become coordinated with each other.

Question 3

3- Importance of detecting movement:
Perceiving events

Answer 3

• Event
  -Segment of time at a particular location that is perceived by observers to have a beginning and an
  end.
• Event boundary
• The point in time when each of these events ends and the next one begins.
• Perception of movement plays an important role in separating activities
  into meaningful events.
  -Event boundaries are more likely to occur when there is change in speed or acceleration of movement.

Question 4

4- Importance of detecting movement:
Social Perception

Answer 4

• Social cues are often linked to movement.
• Heider and Simmel (1944).
• Point-light walkers.
• Centelles and coworkers (2013)
  (1) social interaction: the people were interacting in
  various ways
  (2) non-social interaction: the people were near
  each other but were acting independently. The
  observers were able to indicate whether the two
  people
  -Interacting with each other or were acting independently

Question 5

5- Importance of detecting movement:
Taking action

Answer 5

• Navigating through the environment (safely).
• Watching and playing sports.
• Pouring drinks etc….

Question 6

6- Studying motion perception.

Answer 6

• When Do We Perceive
  Motion:
• Real motion
• Illusory motion
  -Apparent motion
  -No actual motion between
  the stimuli.
  -Movies
  -Television
  -Moving signs
• Induced motion
  -When motion of one
  object (usually a large
  one) causes a nearby
  stationary object (usually
  smaller) to appear to
  move.
  -Example: looks like the moon is coming out but actually the clouds moving in front
• Motion aftereffects
  -When viewing a moving
  stimulus causes a
  stationary stimulus to
  appear to move.
  -Waterfall illusion
  -Word document looks like scrolling up
• Comparing Real and
  Apparent Motion
• Larsen and co-workers (2006)
• three types of displays to a person in an fMRI scanner: control, real, apparent

Question 7

7- Explain the corollary discharge and motion perception.

Answer 7

• The Ecological Approach to Motion Perception
• looking for information in the environment that is useful for perception.
• According to Gibson information is located not on the retina but “out there” in the environment.
• Optic array
  -The structure created by the surfaces, textures, and contours of the environment.
  -He focused on how movement of the observer causes changes in the optic array.
• Figure 8.8a: local disturbance in the optic array.
• Objects are covered then uncovered.
• Because he moves relative to stationary cues movement is perceived.
• Figure 8.8b
• Jeremy’s image is moving across her retina. same local disturbance in the optic array that occurred when Maria was keeping her eyes still.
• Figure 8.8c
• global optic flow; this signals that the environment is stationary and that the observer is moving,
• Everything moves to the left at once signaling no movement.
• Considering the neural signals that travel from the eye to the brain.
• corollary discharge theory
• Three signals
  (1) the image displacement signal, which occurs when an image moves
  across the retina.
  (2) the motor signal, which is sent from the motor area to the eye muscles to
  cause the eye to move.
  (3) the corollary discharge signal, which is a copy of the motor signal.
• Movement will be perceived if a brain structure called the comparator (actually a
  number of brain structures) receives just one signal.
• Figure 8.9a
• There is a CD signal because Maria is moving her eyes
• There is, however, no image displacement signal, because Jeremy’s image stays in the same place on Maria’s retina. The comparator, therefore, receives just one signal, so Maria perceives Jeremy to be moving. (the only way that the stimulus remains stationary on the retina while eyes are moving is if the stimulus is moving).
• Figure 8.9b
• Maria keeps her eyes stationary as Jeremy walks across her field of view.
• There is an image movement signal, because Jeremy’s image is moving across Maria’s retina
• There is no CD signal, because Maria’s eyes are not moving.
• Because only one signal reaches the comparator, movement is perceived.
• Figure 8.9c
• Maria scans the room, there is a CD signal because her eyes are moving and an image movement signal because the scene is moving across her retinas.
• Because both signals reach the comparator, no movement is perceived.

Question 8

8- The Reichardt
Detector

Answer 8

• The Reichardt detector circuit
  -A and B, which send their signals to an output unit that compares the signals
  it receives from neurons A and B.
• Delay unit
  -Slows down the signals from A as they travel toward the output
  unit.
  -The output unit multiplies the responses from A and B to create the movement signal that results
  in the perception of motion.

Question 9

9- Single-Neuron
Responses to Motion

Answer 9

• Middle temporal area.
• Experiments Using Moving Dot Displays
• A coherence increased
• (1) the monkey judged the direction of
  motion more accurately.
• (2) the MT neuron fired more vigorously