wk 8 SP

Question 1

functions of motion

Answer 1

mvement attracts attention

movement of an object relative to an observer provides information about the object’s 3D shape

Movement provides information that helps segregate figures from ground and perceptual organisation (common fate)

Movement breaks camouflage

provides with info to directly interact with environment

informs your heading and time to collision, your movement as well as other objects

Question 2

The ‘correspondence problem’ highlighted by RDKs (Random dot images where we only perceive a moving square when movement between the two is constant)

suggest that

Answer 2

motion detection is direct.

We cannot imagine a visual system matching point for point over time in these displays.

Question 3

5 ways to make a spot of light move

Answer 3

1) Real movement
2) Apparent movement
3) Induced movement
4) Autokinetic movement
5) Movement aftereffects

Question 4

Real movement

how is this detected

Answer 4

Light physically moves
-We percieve movement when the eye is stationary, so the image moves across the retina
- when an image moves across the retina, it stimulates a series of receptors
- There are neurons in the visual system that responds best when a stimulus moves in a particular direction

Question 5

Movement detectors

how do they work + how are they sensitive to direction

Answer 5

neurons are in pairs of neuron and inhibitor in same order and all pairs are wired to one neuron. if light is moving in one direction, it will excite the inhibitor first, not allowing excitation. IF in other direction, light will excite neuron first (won’t get inhibited). If passes over multiple of these pairs, the main neuron will receive successive excitation and will be stimulated

Question 6

movement detectors are sensitive to

Answer 6

direction
speed,

Question 7

how are motion detector (neurons?) sensitive to speed

Answer 7

the distance between the two pairs of receptor-inhibitors.

The excitatory signal travels at a speed that is too fast, the two neurons will be stimulated so that the first neurone’s signal does not reach the main neuron at the same time as the second neuron (will reach before). This will lead to a weaker excitatory response.

The distance between the receptors can be altered to be specific to certain speeds.

Question 8

Bigger seperation of detectors detects ______ motion

Answer 8

faster

Question 9

Aperture problem means

Answer 9

output of all detectors must be integrated at some stage (Medial Temporal Area)

because one of these motion detectors only sees a very small area.

Question 10

Where is the information from motion detectors integrated?

Answer 10

MT (middle temporal area)

Question 11

Threshold for movement detection

depends on

Answer 11

Depends on object and its surroundings,

e.g. with the dot and surroundings (e.g. add vertical lines in space between A & B, lower threshold)

(easier to detect movement when can compare to the lines)

Question 12

Perception of Velocity

affected by

Answer 12

perception of motion velocity. Affected by surroundings plus size of both the moving object and framework through which it moves

e.g. cat in a big cage has to move faster as a mouse in a small cage to appear to be moving the same speed.

Question 13

motion detectors Cannot explain movement perception when:

Answer 13

(1) There is no movement on the retina: as when you follow a moving object with your eyes so your eye movements keep the object’s image stationary on fovea

(2) When you perceive no movement when there is movement on retina: - as when you move your eyes to look at different parts of the scene or as you walk through a scene.

Question 14

Helmholtz outflow theory:

Answer 14

Moving eyes sends signal to eye muscles. Also sends signals to a comparator.
Movement across retina sends signal to comparator
if comparator observes a difference in these signals. do perceive movement

if the two signals cancel each other out, you don’t perceive movement

Question 15

when tracking a car, eyes move but retinal signal remains stationary. is movement percieved

Answer 15

yes, movement is percieved

Question 16

when keeping eyes still and object moves across retina

this is a ____ between signals and therefore we perceive _____

Answer 16

difference

movement

(difference in signals in terms of movement)

Question 17

when we look around the world

what is the comparison between signals of eye movements and of the retina

Answer 17

eye movement and retinal image movement are the same so we perceive no movement

Question 18

Convincing evidence for Helmholtz outflow theory

Answer 18

1. Afterimages move when we move our eyes (Eye muscle movement signal no retinal movement).
2. The world moves when we passively wobble our eyes (retinal movement, no eye muscle movement signal).
3. Immobilizing eye-ball results in attempted eye- movement leading to apparent movement of world in opposite direction (Eye movement signal, no retinal movement).

Question 19

Apparent motion

Answer 19

illusion of movement between two lights by flashing one light on and off, waiting between 40 and 200 msec, then flashing another light on and off

e.g. perception of mvmnt in film = series of static images

Question 20

Less than 30 msec =

Above 30 – 60 msec=

About 60 msec =

About 60 – 200 msec =

Above about 200 msec =

(delay between lights)

Answer 20

no movement, simultaneous.

partial movement

optimum movement

Beta and phi movement

no movement, successive

Question 21

Beta movement =
phi movement =

Answer 21

While movement appears to occur between the two lights, it is difficult to actually perceive an object moving across the space between them. Phi perceive an object between.

Question 22

Distance between two lights also affects perception of apparent movement

as the distance increases, what must be increased to keep the perception of movement
(apparent light)

Answer 22

As distance increases, either the time interval or the intensity of the flashes must be increased to maintain the same perception of movement.

Question 23

induced movement

Answer 23

object isn’t moving, but background is. (or object moving a little bit, background moving a great deal)

e.g. sat on train, think it is moving backwards but actually, train next to you is moving forwards.

Question 24

Autokinetic movement

Answer 24

light moves by itself. e.g. a light without background (in dark) will appear to move in an erratic path

Question 25

Motion after effects

Answer 25

if an observer first views a pattern moving in one direction, and then views the spot of light, the spot (and surroundings) will appear to move the opposite direction

Question 26

how do motion aftereffects work

Answer 26

two neurons sensitive to movement in opposite directions have constant background firing rate.
After prolonged excitation of one neuron, it experiences the inhibitory period where excitation drops below that of other neurons background firing rate.

Therefore we perceive movement in opposite direction