Motion

Question 1

where is motion processed?

Answer 1

in V1, and the dorsal stream

Question 1

why is it important to understand motion?

Answer 1

important to understand how we perceive motion, as this is a survival necessity important in evolution and modern environments

Question 2

where does motion processing begin?

Answer 2

in the retina, into the LGN, and then into the cortex

each successive area processes more complex motion patterns

Question 3

motion processing in V1/2

Answer 3

small receptive fields.
cells respond to simple stimuli and linear motion, but are not tuned or specialised.

Question 4

motion processing in V3

Answer 4

larger receptive fields and specialised for motion of complex stimuli, e.g., texture.

Question 5

motion processing in V5/MT

Answer 5

large receptive fields that respond to motion of anything.
tuned for complex direction and speed, and respond to vestibular cues.

Question 6

motion processing in V6

Answer 6

responds to self-induced motion

Question 6

motion processing in MST

Answer 6

identical to V5, but also respond to static images that imply motion, rather than just simple patterns of motion.

Question 7

what does differentiating between static and moving objects suggest?

Answer 7

we can incorporate information about our own movements when interpreting information in the environment

led to two theories generated

Question 8

sherrington’s eye muscle signal theory

Answer 8

incorporating actual muscle movement information

Question 9

helmholtz’s brain signal theory

Answer 9

intention to move based on outflow signals sent to muscles

Question 10

how are object motions perceived?

Answer 10

relative to the motion of our body, and copies of self-motion signals are sent to motion processing areas of the brain

Question 11

what are time delays required for?

Answer 11

to detect motion happening at the same time

Question 12

what does combining information between areas allow?

Answer 12

for a sense of relative motion – this is called an opponent-motion circuit

Question 13

what do opponent-motion detectors respond to?

Answer 13

the balance between motion cells preferring opposite directions

Question 14

apparent motion

Answer 14

interpreting a set of still images as smooth motion, as long as the time interval and physical displacement are not too large between points A and B

Question 15

wagon wheel illusion demonstrates…

Answer 15

how increases in speed cause changes in the perception of repetitive motion, as larger displacements between faster movements make them harder to link

this results in movements being connected to the closest one, which can generate counterclockwise

Question 16

when does motion sensitivity develop?

Answer 16

10-12 weeks, however certain types of motion, e.g., looming stimuli (things that might collide with the child) are detected even earlier around birth – however these may be later lost and have to be relearnt

Question 17

damage to MT

Answer 17

akinetopsia (motion blindness)

integration of smooth motion breaks down
MT neurons are sensitive to specific direction

Question 18

damage to V1

Answer 18

functionally blind

Question 19

damage to V3

Answer 19

impedes motion perception

Question 20

damage to MST/V6

Answer 20

inhibits navigation

Question 21

MT and speed

Answer 21

MT has specific speed-sensitive neurons, excited for different degrees of speed

Question 22

what can affect estimates of speed?

Answer 22

physical distance from the object being recorded

Question 23

how do neurons measure speed?

Answer 23

degrees per second, rather than actual movement of the item in the environment

Question 24

waterfall illusion (addams, 1834) suggests…

Answer 24

the systems used to identify and encode positions are separate to the systems used for motio

Question 25

what do motion cells in V1 respond to?

Answer 25

image contrast and speed of stimulus

Question 26

what are motion after-effects?

Answer 26

visual illusion experienced after viewing a moving stimulus, and then fixating on a stationary stimulus, which appears to move in the opposite direction to the original

Question 27

how do motion after-effects work?

Answer 27

1. perceived motion is encoded by a population of cells to generate a neural code
2. after prolonged adaptation to a certain direction, these cells reduce their output
3. the neural code for a subsequent static stimulus will be biased in favour of cells that normally respond to the opposite direction of that movement

Question 28

evidence of adaptation in perceptions of speed over time

Answer 28

RGC neurons increase dramatically when motion first occurs, but then drops down in excitement

once motion is finished, the neuron inhibits below initial baseline activity

Question 29

evidence of adaptation in perceptions of speed over space

Answer 29

fovea is sensitive to changes in speed – important for processing information, however after 10s of movement in the periphery, we stop seeing this motion entirely

Question 30

when are speed judgements more accurate?

Answer 30

before adaptation, than afterwards

Question 31

what happens to motion in the periphery?

Answer 31

fades over time

Question 32

principle of univariance

Answer 32

cells cannot differentiate between speed and contrast

since motion cells can only have one output, they cannot signal two different things, e.g., contrast and motion

Question 33

how can PoU affect perceptions of speed?

Answer 33

if neurons are driven by more than one input, they are unable to differentiate between high-low or low-high speed and contrast

Question 34

can perceived speed reduce with reduced contrast?

Answer 34

for some stimuli, e.g., looming and receding objects

Question 35

motion contrast in MT

Answer 35

their centre-surround cells activate to motion in the centre, but are inhibited if the same motion occurs in the periphery

therefore, cells are only excited when there is the same direction of motion

Question 36

snow blind illusion

Answer 36

shows how motion-contrast cells can affect speed and motion perception, as motionless stripes covering background excite the motion-contrast cells and suggest higher speed

Question 37

when is induced motion and vection common?

Answer 37

when motion is slight and acceleration is smooth, by creating uncertainty as to whether it is us moving or the environment

Question 38

drum experiment

Answer 38

shows the sickness reflex is caused by vection due to conflict between visual and vestibular (used for balance) cues

Question 39

illusory motion (leviant, 1981)

Answer 39

the sensation of motion in a static stimulus

MT cells are active when viewing the image stripes which over-excite the orientation cells and pass a motion signal

Question 40

aperture problem

Answer 40

involves only seeing motion at right angles to the edge, when viewing a moving stimulus through a small window (aperture)

distorts the true direction of motion perception

Question 41

what do motion cells in V1 only respond to?

Answer 41

short edges
meaning they can only signal motion at right angles to their preferred orientation

cells in MT must integrate these signals to derive the true motion, but they can be fooled.