motion perception (illusions)

Function of motion perception

• Helps break camouflage

• Helps attract attention

• Helps segregate objects from the background

• Help us interpret events

• Help us determine the structure of objects

• Help us determine what actions people are performing

Break camouflage, attract attention, segregate objects

Camouflaged animal can be virtually invisible until it moves

When it moves, attention is attracted to it and its camouflage is broken

So motion attracts attention and helps us segregate objects from the background

Interpret events

By seeing how objects a interact, you can infer causality relationships and even social relationships (video of triangle chasing circle and destroying home)

Structure from motion

Motion allows us to infer 3D shape

Interpreting actions

While static poses are often ambiguous, when someone moves, their actions and intentions are often made clear

Using Point-Light “walkers” can infer motion stimuli is doing

Life without motion perception

Condition known as akinetopsia - cannot see cars moving, but when look down then up see that car has moved

People without condition - looking at ship on horizon, looks like not moving, but when you look down then up after a while, ship has moved

When do we perceive motion?

• Real motion (something actually moving)

• Illusory motion (nothing actually moving)

  • Static image

  • Apparent motion

• Motion aftereffects

• Induced motion

  • Moving background (or a moving object) causes a stationary object to appear to move

Static illusion

Picture seems like its moving even though it isn’t

Apparent motion

Series of stationary images are presented, making it seem like motion is happening

Motion after effect

Waterfall, look like rock face is moving upwards

Induced motion

Nearby object (usually a large one) either affects the perceived motion of a second object (usually a small one) or causes a second object to appear to move

Motion induced blindness

Makes it harder to notice changes - dots are stationary, very easy to notice them changing colour; but when moving harder to detect colour change

When things are moving, there are transient signals associated with all objects - not just the one changing, thus, attention is no longer drawn preferentially to the changing objects, so the changes are not noticed

Motion illusion

Footsteps illusion - moving at same speed, but looks like footsteps movement because of contrast in colour and ‘foot’

Aperture problem - cant see end of line, movement of line is ambiguous

Barber pole illusion - appears to be more vertically always