Ch 7: Perceive Motion

Question 1

Moment provides info one 4

Answer 1

> Orientation and navigation
calculating direction of heading
`avoiding/catching approaching objects
Separation of figure and ground
introduction of movement defines an object
Defining object shape
successive views can be integrated into a full percept
Called structure from motion
Attracting attention
detection of moving object is easier than detecting same target when stationary

Question 2

5 types of motion

Answer 2

-“Real” movement
light physically moves
-Motion aftereffects
moving stripes are viewed prior to viewing the light
light appears to move in the opposite direction of the stripes
-Apparent movement
lights flashed one after the other with 40-200 msec separation
-Induced movement
light surrounded by larger object which is moved
-Biological motion

Question 3

Real movement

Answer 3

1) something moves in the world - image moves across the retina
2) Things not explained by above
Examples:
something moves and we track it - doesn’t move across the retina
We move our eyes or body – movement of the image across the retina but we don’t perceive movement

Question 4

Retinal Image Motion

Answer 4

Specialized motion sensitive mechanisms must represent speed & direction
Reichardt detectors - most modern models elaborate on this type of detector

Question 5

directionally selective circuit:

Answer 5

Assume that detector cell (D) responds when it receives simultaneous input from receptors R1 and R2.
By introducing a delay element (t), detector would only respond to a target moving in one direction

Question 6

A velocity-selective circuit

Answer 6

Depending on the delay, this cell would only respond to a certain speed of movement

Question 7

Aperture Problem

Answer 7

Prob: The impossibility of determining the actual direction of motion of a stimulus by the response of a single neutron that sees the stills only through a small window and sees inly the component of motion in the bourbons preferred direction.
Solution: Responses of a number of V1 neurons are pooled
This may occur in the medial temporal (MT) cortex, which is located in the where/action stream

Question 8

Dorsal Pathway

Answer 8

Where/how

V2–>MT (motion)–>parietal cortex (perceiving space/motor, coordinating visual/motor interactions)

Question 9

Mechanisms for Detection Motion

Answer 9

RF or MT neurons are 5-10 times larger than V1 neurons
MT neurons tuned to motion, but not curvature, colour, or shape
Lesions in MT impair motion processing

Question 10

Lesions to MT, can’t see motion

Answer 10

Akinetopsia

Question 11

Psychophysical Evidence

Answer 11

Selective adaptation (measure contrast thresholds before and after adaptation)
-direction specific
–adapting to a gratings/bars moving in one direction, elevates the threshold for gratings/bars moving in the same direction
-velocity specific
–most threshold elevation is found for gratings moving at the same speed
Suggests populations of direction and velocity selective neurons

Question 12

Case 2

Answer 12

An object moves, and the observer follows the object with his or her eyes
Retinal image is stationary and yet object is perceived as moving
An observer moves the eye, object is stationary
Retinal image moves and yet object is perceived as stationary

Question 13

Eye movements: 2 types

Answer 13

version eye movements
-Pursuit movement - Tracking objects through space
[Slow & smooth]
-Saccades - fixating on different parts of a scene
{Saccadic suppression & transsaccadic integration (change blindness)]
[Fast, jerky & very frequent]
vergence eye movements
(shift of movement from close up to far away/vise versa)

Question 14

Corollary Discharge Theory- 3

Answer 14

Movement perception depends on three signals
-Motor signal (MS) - signal sent to eyes to move eye muscles (from the supirior colliculous)
-Corollary discharge signal (CDS) - copy of the motor signal
-Image movement signal (IMS); movement of image stimulating receptors across the retina
Movement is perceived when comparator receives input from either corollary discharge or image movement signal
Movement is not perceived when comparator receives input from both corollary discharge and image movement signals

Question 15

Physiological Evidence for Corollary Discharge Theory

Answer 15

Damage to the medial superior temporal area in humans leads to perception of movement of stationary environment with movement of eyes
Real-movement neurons found in monkeys that respond only when a stimulus moves and do not respond when eyes move

Question 16

Motion aftereffects

Answer 16

A case in which we see motion when there is none present

Question 17

Apparent Motion

Answer 17

occurs when 2 or more lights are flashed in sequence
Depending on the interstimulus interval and the spatial arrangement of the lights, different forms of illusory movement are seen

Question 18

Shortest-path constraint

Answer 18

apparent motion tends to occur on the shortest path between two stimuli

Question 19

Induced movement:

Answer 19

is the incorrect attribution of movement e.g. sitting next to train that moves, moon in clouds, etc.
Occurs typically when larger object moves relative to a smaller one (frame of reference)

Question 20

The kinetic depth effect

Answer 20

When the shadow of a rotating 3D object is cast on a screen, it looks three-dimensional, even though the shadow is flat. 


Question 21

Biological motion (where)

Answer 21

Neurological studies show biological motion is processed in the superior temporal sulcus (STS)
If small lights are attached to joints, we are able to extract information about what a person is doing if the individual is moving
movement of person or other living organism
Point-light walker stimulus - biological motion made by placing lights in specific places on a person
Structure-from-motion takes place with point-light walkers