lecture 8

Question 1

evolutionary importance of movement

Answer 1

• probably evolved very early
• movement= life
• predators that can detect movement of prey is more likely to catch it
• prey that can detect the movement of predators more likely to survive
• many animals have poor shape, depth and colour perception
• none lack the ability to perceive movement

Question 2

what are the functions of movement?

Answer 2

1) attracts our attention (active or passive)
2) movement of an object relative to an observer provides information about the objects 3D shape
3) movement provides information that helps us segregate figure from ground and perceptual organisation (common fate)
4) movement breaks camouflage (freeze reflex)
5) movement provides information that enables us to actively interact with the environment
6) informs of your heading and time to collision, your movement as well as other objects

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 after effects

Question 4

what problem is highlighted by random dot kinematograms, what does this suggest?

Answer 4

correspondence problem
suggest that motion detection is direct, as we can not imagine a visual system matching point for point over time in these displays

Question 5

how do random dot kinematograms work? what do we perceive?

Answer 5

instead of presenting each simultaneously to each eye, we now present the first and then the second after a short time lag

this causes us to perceive movement of a stimulus, even though we can not perceive a stimulus in either frame alone

Question 6

real movement

Answer 6

we perceive movement when the eyes are stationary, so that the image moves across the retina

Question 7

what happens when an image moves across the retina

Answer 7

it stimulates a series of receptors

Question 8

what do some neurons in the visual system respond best to?

Answer 8

when a stimulus moves in a particular direction and speed

Question 9

movement detectors

Answer 9

receptors that are stimulated when an image moves across the retina

Question 10

what interact to create a cell that only responds to movement from right to left

Answer 10

excitation and inhibition

Question 11

what happens if you change the order of delay in a Reichardt detector

Answer 11

it becomes specified to movement in the other direction

Question 12

Reichardt detector

Answer 12

neural circuit that detects movement viewed by a stationary eye , proposed by Werner Reichardt

Question 13

what does the Reichardt detector consist of

Answer 13

two neurons, A and B

Question 14

where do neurons A and B (Reichardt detector) send their signal?

Answer 14

to an output unit

Question 15

what is the function of the output detector?

Answer 15

compares the signals it receives from neurons A and B

It multiplies the responses from A and B to create the movement signal that results in the perception of motion

Question 16

what is the purpose of delay unit in Reichardt detector?

Answer 16

to slow down the signals from A as they travel towards the output unit

Question 17

when will a signal be produced by the Reichardt detector?

Answer 17

when the signal passes A first and travels at the right speed, so that the signals from A and B reach the output unit at the same time

Question 18

what stops a response being produced in the Reichardt detector?

Answer 18

1) when something moves in the wrong direction

2) when something goes at the wrong speed

Question 19

what happens if you change the spacing of the detectors in a Reichardt detector?

Answer 19

they respond to different speeds

bigger separation detects faster motion

Question 20

where have Reichardt detectors been found?

Answer 20

insects and frogs

Question 21

do we have Reichardt detectors? if so where?

Answer 21

we have similar cells in the cortex, which are sensitive to different orientations, speed and direction of movement

Question 22

what does the aperture problem mean ?

Answer 22

output of all detectors must be integrated at some stage

Question 23

what is the aperture problem?

Answer 23

that the neurons receptive fields function like an aperture, only revealing a small portion of the scene

Question 24

can we determine direction of movement through our ‘aperture’?

Answer 24

yes, as correlated movement of random dots increases, neurons in the middle temporal area fire more

Question 25

monkey experiment on medial temporal lobe

Answer 25

let monkey to learn to point to the direction of movement (press up button when 100% correlated up in aperture)
stimulate monkeys MT neurons without showing visual stimuli
monkey still presses the up button

Question 26

velocity transposition

Answer 26

show to images moving across the visual field at different speeds can be perceived to moving at the same speed

Question 27

what is threshold for detecting movement dependent on?

Answer 27

an object and its surroundings

Question 28

how can you lower the threshold for movement detection?

Answer 28

add vertical lines in space between point A and pint B

Question 29

what is perception of velocity effected by?

Answer 29

surroundings

the size of the moving object and the framework through which it moves

Question 30

when can movement detectors not explain motion perception?

Answer 30

when there is no movement on the retina

when you perceive no movement when there is movement on the retina

Question 31

how there be motion when there is no movement on the retina?

Answer 31

as you follow a moving object with your eyes the eye movements keep the objects image stationary on you fovea

Question 32

how can there be no movement when an object is moving on your retina?

Answer 32

when you move your eyes or look at different parts of a visual scene/ walk through a scene

Question 33

what is Helmholtz outflow theory?

Answer 33

if afferent signal (movement signal from retina) cancels out efferent signal (signal to eye muscles), no movement of has occurred. If they do not match, movement is perceived

Question 34

evidence for Helmholtz outflow theory

Answer 34

1) after images move when our eyes move,
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) immobilising eyeball results in attempted eye movement, leading to apparent movement of world in opposite direction
eye movement signal, no retinal movement

Question 35

another name for apparent movement

Answer 35

stroboscopic movement

Question 36

what is apparent movement?

Answer 36

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

Question 37

what media relies on apparent movement

Answer 37

film: series of static images perceived as movement

Question 38

apparent movement when delay between images is: less than 30 msec

Answer 38

no movement, simultaneous

Question 39

apparent movement when delay between images is: above 30- 60 msec

Answer 39

partial movement

Question 40

apparent movement when delay between images is: about 60msec

Answer 40

optimum movement

Question 41

apparent movement when delay between images is: about 60-200 msec

Answer 41

beta and phi movement

Question 42

beta movement

Answer 42

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

Question 43

phi movement

Answer 43

perceive an object between

Question 44

apparent movement when delay between images is: above 200msec

Answer 44

no movement, successive

Question 45

what changes need to be maid to maintain same perception of apparent movement as distance between two lights increases?

Answer 45

time interval or intensity of flashes must be increased

Question 46

induced movement

Answer 46

surround spot with another object, then move the other object

Question 47

everyday example of induced movement

Answer 47

sitting on a train, feeling it move backwards, only to realise your train is still and the one next to you is moving forward

Question 48

autokinetic movement

Answer 48

when the surrounding framework of a room is not visible, the small stationary light appears to move, usually in an erratic path

Question 49

sherif (1935) autokinetic study results

Answer 49

individually: dot moved from 0.8 inches to 7.4 inches
group: all reported dot moved 4 inches

Question 50

suggested cause of autokinetic effect

Answer 50

control of eye movements not completely stable in the dark?

Question 51

movement after effects

Answer 51

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

Question 52

waterfall illusion

Answer 52

anstis & gregory (1964)
depends on movement of stripes across the retina
supports the idea of movement detectors, which respond only to movement across the retina

Question 53

ratio hypothesis

Answer 53

sutherland (1961) argued that motion after-effects arose from an imbalance in the ratio of the activities form two sets of directionally-tuned receptors, each sensitive to the opposite directions of motion

Question 54

who produced evidence to support the ratio hypothesis? when?

Answer 54

Barlow & Hill (1963)

Question 55

event perception

Answer 55

movement provides information about 3D shape, helps us to segregate figure from ground an interact with the environmet

Question 56

motion blindness

Answer 56

when a global moving pattern surrounds a high contrast stationary target stimulus , the target disappears and reappears alternately for durations of several seconds