L7 - Motion

Question 1

Do animals have motion perception?

Answer 1

• All animals have motion perception as it is fundamental - it can go wrong
• We can get motion from things that do not move - same for all creatures

Question 2

Do we really detect motion?

Answer 2

• (seeing motion when it’s not there)Spooky movements - motion aftereffects: closing eyes then bob moves, he has moved, or the direct measure of motion = spiral contraction causes expansion on Bob’s head = saw the motion, no change in position
• (not seeing motion when it is there) Apparent motion breakdown/disco - Strobe lights - where we see pictures without flow
• Motion blindness: set of stationary images for movement for everything - like the disco but permanently = from brain damage

Question 3

Explore apparent motion:

Answer 3

• Demonstration of motion and helps understand how we extract motion
• Present dots on three movie frames but you see one moving dot like TV and movies
• Timing and spacing are all important to produce motion (jump = the displacement from one image to another)

Question 4

What are motion detectors:

Answer 4

• Motion detector is also known as the delay and compare model
• 2 receptive fields, a&b on the retina
• Ability to delay one of the signals and a comparator (multiplication/correlation)
• When you shine light in receptive field A = fires, light continues and gets to B = fires
• As A fires, the impulses come down and get stuck in the time, but B fires so that both reach the comparator at the same time or roughly the same time, this time period reflects what you see
• But when the light comes in the other direction, there are massive delays as stimulation disappears making the whole system weaker = tells difference in movement in direction
• Scheme developed in 50s to explain flight of beetle
• Seen in most animals with motion perception

Question 5

What are random dot patterns?

Answer 5

• Each square is coloured either blue or white and is meant to be random
• So many dots you cannot keep track of each one = reduce ability to identify what moved = lowers the motion stuff

Question 6

What did Braddick do?

Answer 6

• Subjects tried to identify the orientation of a moving area of dots
• Only possible if there is a small displacement (<0.25 degree), time intervals (<100ms) and present pattern to the same eye
• Can see in movies but not with the pictures side to side
• AM can be detected by two methods: Short range process: relying on response of low-level motion detectors
• Long Range Process - cogn processes that tracks features from 1 position to another

Question 7

What are direction selective cells?

Answer 7

• All tested animals have direction selective cells
• Frogs show that they do not respond to stationary targets (cannot see stationary items) but they have cells in the retina to moving blobs
• Monkeys have no directionally selective cells found in retina or LGN - some cells in V1 are directionally selective (fed by magnocellular cells in the LGN)

Question 8

What are the visual areas of the monkey?

Answer 8

• Area MT (or V5): very small
• Contains maps of the world and contains all receptive fields
• Each cell has directionally selective
• STUDY: made animal look at fixation point, had already found receptive field of the cell, measured a random moving dot pattern, each cell fires to one particular direction. They are highly organised, every cell reflect as one if you go down, and slightly different direction across (like hypercolumns)
• Found that neurones in Area MT show strong directional selectivity

Question 9

What was a study about apparent motion with a cell in Area MT?

Answer 9

• Monkey looks at fixation point and map out receptive field of one neurone and worked out preferred direction, flashes of bars are shown that can be moved in preferred or opposite direction as well as size of jump and intervals between them
• RESULTS: Long time between flashes, cells respond to every single light for both directions, but short time between flashes = huge response from pref direction but not null. Cell has a t-max about 100ms = Highly directionally selective in those conditions

Question 10

What was a study looking at Human MT imaging studies?

Answer 10

Looked at stationary vs moving dots and take away activity from stationary from moving and found two areas: v1/v2 and the v5 (also known as MT)

Question 11

What was a study of the enigma?

Answer 11

• Looked at brain activity at some illusory motion, control was modified version that didn’t elicit the motion, same area is activated by both patterns but some regions adjoining V5 are also active
• Little to no activation of striate region
• Activation of V5 seems enough to elicit motion in humans
• Doesn’t tell us why this illusion occurs.
• When MT fires = we see motion

Question 12

What is motion blindness?

Answer 12

• LM had normal on test of acuity, colour vision, object recognition, binocular vision later studies show reasonably normal spatial and temporal contrast sensitivity
• BUT she cannot see motion aftereffect, no apparent motion, poor pursuit eye movement
• Fails to segment scene by motion and looks like a MT lesioned monkey
• No two patients will ever be the same

Question 13

What is the link between speed and MT?

Answer 13

• MT neurones also appear responsive to speed (amount of activity)- but also responsive to contrast (black to white)
• May mistake less firing due to change in contrast as less firing is because of ‘less motion’
• Things appear to slow down as contrast is reduced

Question 14

What was a study based on slower firing and contrast?

Answer 14

• Ppts taught to drive In sunny conditions then asked to drive at set speeds under diff levels of fog
• Drove faster the foggier it got (fog = less contrast = feels slower but actually going faster), helps explain motorway madness