5. Motion Flashcards
Optic flow
A motion depth cue where objects appear to change in size as we move toward or away from them
Six reasons that we need motion perception
- Optic flow / self motion
- Object motion
- Controlling action
- Figure-ground segregation
- Cues to shape of objects
- How far away things are (via motion parallax)
These are all reasons that _________________
Motion parallax
A monocular depth cue arising from the relative velocities of objects moving across the retina of a moving person.
In motion parallax:
When we ______, we change viewpoint, and close objects move _______ than distant objects.
In motion parallax:
When we move, we change ________, and ________ objects move faster than ________ objects.
In motion parallax:
Objects closer to you than your point of fixation move __________________. Objects further than your point of fixation move ______________________.
In motion parallax:
Objects _______________ move backwards, against the direction you are moving. Objects _______________ move with the head.
Many animals use motion parallax to __________.
Many animals use __________ to infer depth.
Motion is not just displacement over space and time. How do we know this?
We can see motion even between:
- two lights too close in space to resolve as being separate flashes
- flashes too close in time to tell that there were two events
What does this tell us?
Motion analyses are ______, _________ and _________.
______ ________ are early, independent and sensitive.
What is akinetopsia?
Motion blindness - a patient cannot perceive motion in their visual field, despite being able to perceive stationary objects without issue. They see the world like a series of snapshots.
What is this disorder called?
What are three problems someone with akinetopsia might experience in their everyday life?
- Crossing roads
- Pouring tea
- Tracking conversations
What visual disorder would cause problems with these?
What do we mean by functional segregation of motion, and what evidence do we have for it?
Motion can be destroyed while spatial vision and temporal estimation are retained. This is called ______________. Akinetopsia gives us evidence that we have dedicated brain areas for motion.
Why is akinetopsia rare?
___________ can only occur if there are lesions in the MT on both sides of the brain, which means it occurs rarely.
What brain area specialises in motion processing, and what stream is it part of?
MT specialises in __________, and is part of the dorsal (“where”) stream.
Five properties of receptive fields of the magnocellular neurons in MT
Properties of receptive fields of the _________ neurons in _________:
- Large
- Sensitive to motion
- Rapid response
- Colour blind
- Low spatial resolution
Motion aftereffect
The __________ is a visual illusion experienced after viewing a moving visual stimulus for a time with stationary eyes, and viewing a stationary stimulus.
The stationary stimulus appears to move in the opposite direction to the original (physically moving) stimulus.
Why does the motion aftereffect occur?
The ___________ occurs because of adaptation - the tendency of cells to reduce or recalibrate their response after prolonged stimulation.
Why is adaptation an important psychophysical tool?
__________ is an important ___________ because it may produce bias. Bias can be used to infer how neurons are encoding information and interacting with one another.
How the motion aftereffect works:
- Perceived motion =
- At rest:
- During adaptation:
- Due to adaptation:
- Since they are imbalanced, __________.
How the motion aftereffect works:
- __________ = relative activity in pairs of neurons tuned to opposite directions.
- __________: Both fire weakly, no motion perceived.
- __________: one is activated more than the other.
- __________: one is subsequently depressed more than the other.
- ________________, motion is seen in the opposite direction.
Perceived motion (and the motion aftereffect) use direction selectivity and ___________.
Perceived motion (and the motion aftereffect) use ___________ and opponency.
Your ability to see things change and to ___________ are quite mixed up with each other. _________ can cause change blindness.
Your ability to see things _________ and to see things move are quite mixed up with each other. Motion can cause __________.
The footstep illusion shows two bars moving across high contrast stripes. The bars look like they are “stepping”, but really they are moving smoothly. How does this work?
____________ works by changes in luminance over time. At low contrast, the bars appear to move slower, and at high contrast, they appear to move faster.
This makes the bars look like they are _________ when really they are ____________.
Motion processing operates by signalling change in _______, not _______.
Motion processing operates by __________ in time, not space.
What does this diagram show?
Vertical orientation in space-space.
The right half of the stimulus is lit, the left half is dark.
What does this diagram show?
Horizontal orientation in space-space.
The top half of the stimulus is dark, the bottom half of the stimulus is lit.
What does this diagram show?
Tilted orientation in space-space.
The left side of the stimulus is lit at a tilted angle. This means that there is variation in both directions (ie. along the x and y axis).
What does this diagram show?
Static orientation in space-time.
The right half of the stimulus is lit, and this doesn’t change - it varies in space, but doesn’t vary in time.
What does this diagram show?
Flash orientation in space-time
Full field of light, stays on for a while and then switches off - it varies in time, but doesn’t vary in space.
What does this diagram show?
Drift orientation in space-time.
A vertical (not tilted!) light bar starts on the left and drifts over to the right. Variation in both directions: space and time.
Orientation in spacetime = ______________.
Direction = ___________ in ____________.
Receptive fields that are selective for space-time orientation have a velocity preference (i.e. some receptive fields prefer slow movement, and some prefer fast movement).
What is the problem with this, and how do we solve it?
Receptive fields that are selective for _________ have a __________.
The problem with this is that a “slow” space-time filter might respond to static things too.
The solution is opponency: taking the difference between it and an equally but oppositely oriented receptive field.
Name two consequences of using opponency to process space-time orientation.
- Apparent motion
- Four-stroke apparent motion
Are both consequences of ________________.
Describe apparent motion.
- motion cells are unable to tell “real” (continuous) motion from “________” (discrete) ________.
- a consequence of using opponency to process space-time orientation.
What is four-stroke apparent motion?
_____________ is the illusion of constant motion in one direction based on 4 repeated images.
What happens in each frame of four-stroke apparent motion?
- From frame 1 to 2: the motorcycle moves forward.
- From frame 2 to 3: moves backwards but reverses contrast (flips polarity).
- From frame 3 to 4: moves forwards again
- From frame 4 to 1: moves backwards, reversing contrast (flipping polarity) again.
This creates the illusion of ___________.
What is the basis of the four-stroke apparent motion illusion (a consequence of using oppenency to process space-time orientation)?
- Motion detectors are effectively stimulated in one direction.
- This is because the pattern of alternation in contrast in space and time aligns with the receptive field of a motion detector tuned to the direction of the perceived motion.
This is the _________________, one consequence of __________________.
Reverse card!
Motion blindness - a patient cannot perceive motion in their visual field, despite being able to perceive stationary objects without issue. They see the world like a series of snapshots.
What is this disorder called?
What is akinetopsia?
Reverse card!
____________ works by changes in luminance over time. At low contrast, the bars appear to move slower, and at high contrast, they appear to move faster.
This makes the bars look like they are _________ when really they are ____________.
The footstep illusion shows two bars moving across high contrast stripes. The bars look like they are “stepping”, but really they are moving smoothly. How does this work?
Reverse card!
Vertical orientation in space-space.
The right half of the stimulus is lit, the left half is dark.
What does this diagram show?
Reverse card!
Horizontal orientation in space-space.
The top half of the stimulus is dark, the bottom half of the stimulus is lit.
What does this diagram show?
Reverse card!
Tilted orientation in space-space.
The left side of the stimulus is lit at a tilted angle. This means that there is variation in both directions (ie. along the x and y axis).
What does this diagram show?
Reverse card!
Static orientation in space-time.
The right half of the stimulus is lit, and this doesn’t change - it varies in space, but doesn’t vary in time.
What does this diagram show?
Reverse card!
Flash orientation in space-time
Full field of light, stays on for a while and then switches off - it varies in time, but doesn’t vary in space.
What does this diagram show?
Reverse card!
Drift orientation in space-time.
A vertical (not tilted!) light bar starts on the left and drifts over to the right. Variation in both directions: space and time.
What does this diagram show?
Reverse card!
- From frame 1 to 2: the motorcycle moves forward.
- From frame 2 to 3: moves backwards but reverses contrast (flips polarity).
- From frame 3 to 4: moves forwards again
- From frame 4 to 1: moves backwards, reversing contrast (flipping polarity) again.
This creates the illusion of ___________.
What happens in each frame of four-stroke apparent motion?
Reverse card!
- Motion detectors are effectively stimulated in one direction.
- This is because the pattern of alternation in contrast in space and time aligns with the receptive field of a motion detector tuned to the direction of the perceived motion.
This is the _________________, one consequence of __________________.
What is the basis of the four-stroke apparent motion illusion (a consequence of using oppenency to process space-time orientation)?
