Motion Perception

Question 1

Retinal velocity

Answer 1

Change in visual angle per unit of time

Question 2

How do we categorize perceptual motion (fastest or slowest)?

Answer 2

threshold in terms of a velocity

e.g. threshold could be defined as the velocity at which motion is detected 50% of the time

Question 3

subject-relative motion

Answer 3

motion of a single visible object with no background reference

Question 4

object-relative motion

Answer 4

motion of a visible object relative to some other object or visible background.

Question 5

what are the two sources of information or multiple situations that lead to perceived motion?

Answer 5

retinal displacement and optic pursuit

Question 6

Optic pursuit

Answer 6

occurs when we track a moving object with our eye

- the image stays on the fovea, yet we perceive it as moving

Question 7

Retinal displacement

Answer 7

the changing position of an object’s image on your eye

- eye stays still but image moves

Question 8

Apparent motion

Answer 8

when images flash on and off in separate locations with certain timing relations. although nothing really moves between the flash locations, motion is seen.

e.g. watching motion on TV

Question 9

Other words for apparent motion

Answer 9

• stroboscopic motion

- beta motion

Question 10

Interstimulus Interval (ISI)

Answer 10

the time between the end of one flash and the start of another (to create apparent motion)
* measured in ms

Question 11

How do different measurements of ISI, or time, impact apparent motion?

Answer 11

For a specific spatial disparity:

ISI < 60 ms, SIMULTANEITY is seen.
ISI 60-200 ms: OPTIMAL MOVEMENT is seen. (smooth and continuous)
ISI >200 ms: SUCCESSION, not movement, is seen.

Question 12

Induced motion

Answer 12

involves an object and a surrounding reference frame. when the surround or frame moves, the object appears to move.

*induced motion may also make the observer feel they’re moving

Question 13

What are the two general theories of motion perception?

Answer 13

1) Indirect Perception Theory

2) Direct Perception Theory

Question 14

Indirect Perception Theory

Answer 14

Motion is not a basic perceptual quality; it is derived from other things

*in order to perceive motion, your brain must first calculate other things –> motion is indirectly calculated from those things

Question 15

Direct Perception Theory

Answer 15

Motion is a basic perceptual quality. Your system is wired to perceive it.

Question 16

What are the two experiments that ended the indirect vs direct perception debate?

Answer 16

Exner and Wertheimer

Question 17

Exner experiment

Answer 17

If the processing of motion is indirect, it would have to depend on people’s processing of time

• tested:
  1) temporal order tasks: how good people are at processing time; which shape comes first
  2) how good at motion: how well people can tell the direction of motion

Question 18

Conclusion of Exner experiment

Answer 18

Threshold for perceived succession:
BELOW 45 MS - can’t tell the temporal order of two successive flashes
BUT: can tell the direction of apparent motion with as low as 14 MS

Result: people are able to perceive motion even when they have no access to time information –> PROCESSING OF MOTION IS INDEPENDENT OF TIME
*proof of direct perception debate

Question 19

What are the thresholds for perceived succession according to the Exner experiment

Answer 19

Threshold for perceived succession:
BELOW 45 MS - can’t tell the temporal order of two successive flashes
BUT: can tell the direction of apparent motion with as low as 14 MS

Question 20

Objectless Motion

Answer 20

When there is an experience of simultaneity (small ISI), we perceive both objects stationary
HOWEVER we still appear some motion with no shape

Question 21

Wertheimer’s Experiment

Answer 21

If we can perceive motion without telling what is moving (no spatial displacement, time, no access to delta x and t), then motion is direct and calculated with no circuitry

-objectless motion

Question 22

Phi Motion

Answer 22

Only occurs when ISI is so small, that we perceive simultaneity

(def) at very small ISIs, one sees simultaneous lights but also sees something moving between them. indicates that motion perception mechanism is triggered independently of the perception of a single object from the two flashes

Two simultaneous percepts
– OFF AND ON IN FIXED LOCATIONS + MOTION – “OBJECTLESS” MOTION

Question 23

Which perceptual theory is correct?

Answer 23

DIRECT Perception Theory is correct

Motion is a basic perceptual property. We are wired to perceive it from the retina (before brain)

In the ganglion cells, they are arranged to encode motion

Question 24

If delay is long…

Answer 24

The movement must be slow in order for the delay neuron to be activated

Question 25

What are Reichardt Detectors?

Answer 25

Direction sensitive motion mechanisms

• • The basic requirement for velocity detection
• • Opponent process arrangement to determine net motion

Algorithm:
Register: CHANGE AT LOCATION 1
– elapsed time –
Register: CHANGE AT LOCATION 2

Question 26

Motion aftereffects

Answer 26

Occurs when detector gets fatigued from a certain direction of motion. When movement stops, the balance between the two directions is off, and we perceive motion in the direction of the non-fatigued, spontaneously firing neuron.

– Suggests opponent process arrangement in Reichardt Detectors

Question 27

What is an example of motion aftereffects?

Answer 27

waterfall illusion

Question 28

Explanation for stepping feet illusion

Answer 28

Magno-cellular pathway (for motion) does not see color, only luminance –> so stepping motion is only seen when luminance is the same for all blocks of color in the demo