Cours 6 - Perception du mouvement - Chapitre 10 Flashcards
What are the 4 learning objectives of Chapter 10?
1) Understand how motion modulates vision
2) Define movement & compare models
3) Explain motion perception challenges
4) Compare roles of ocular movements
What does Gestalt psychology say about motion illusions?
The whole is greater than the sum of its parts; perception is more than individual elements.
What visual pathway is most relevant to motion perception?
The dorsal stream.
How is motion defined perceptually?
As a spatiotemporal event (change in position over time).
Why is motion perception essential for figure-ground segmentation?
Movement makes camouflaged or hidden objects easier to detect.
What roles does motion play in daily life?
Helps guide action, judge distance, recognize 3D shape, avoid danger, and read facial expressions.
Why can’t we rely on absolute distance or speed for motion perception?
Because we’re bad at estimating absolutes; instead, we track image size changes.
Why are light intensity signals (e.g., from rods/cones) unreliable?
They’re too noisy—like shadows from clouds can alter perception.
What is needed to perceive motion from flickering dots?
Optimal flicker speed and appropriate distance between stimuli.
What happens if flicker is too fast or too slow?
Too fast: illusion breaks. Too slow: no motion perceived.
How does the brain create smooth motion perception?
It samples positions at different times and interpolates changes.
What’s the basic motion detector model?
Neurons A & B activate neuron M if a stimulus crosses both receptive fields.
What are 2 issues with the basic model?
1) No direction selectivity
2) Can’t distinguish between motion and static presence
How do Reichardt detectors solve this?
They add a delay via interneuron D, enabling direction and speed selectivity.
Where are Reichardt detectors found in primates?
In V1, not the retina.
What does the motion aftereffect tell us?
Motion processing happens in the cortex and shows interocular transfer.
What is the aperture problem?
Small receptive fields misinterpret direction of motion (e.g., detecting only rightward motion).
What is apparent motion?
Illusion of real movement from sequential flickering of two dots.
What is the wagon wheel effect?
When repeated frames create an illusion of backward movement—due to matching errors.
What is the correspondence problem?
Matching features across frames to track continuous motion is complex.
What helps the brain solve the correspondence problem?
Proximity, similarity in color, orientation, and spatial frequency.
Which brain region solves this problem?
Area MT (V5) in the extrastriate cortex.
What does Area MT do?
Integrates motion input from multiple V1 neurons to determine global motion.
What did Newsome’s dot experiment show?
Monkeys could detect global motion with only 3% coherence, and performance matched MT neuron activity.
What is akinetopsia?
Motion blindness due to bilateral damage to area MT—moving objects appear frozen.
Is vision passive or active?
Active—our eyes move constantly to gather visual info.
What is smooth pursuit?
Voluntary eye movement to follow moving objects, stabilizing their image on the fovea.
What is area MST responsible for?
Detecting motion resulting from voluntary eye movements.
What did Stevens’ experiment with curare reveal?
Attempting to move paralyzed eyes caused the world to appear in motion—proving MST’s role.
What happens when MST is damaged?
Vertigo, nausea, and failure to distinguish between object and self-motion.
What are saccades?
Rapid, jerky eye movements to change fixation—voluntary or involuntary.
What are microsaccades?
Tiny eye movements preventing visual fading and enhancing detail.
What is saccadic suppression?
The brain dampens visual input during saccades to prevent motion blur.
Which brain areas are suppressed during saccades?
Area MT and surrounding parietal regions.
Which illusion is enhanced by saccades?
The rotating snakes illusion—stronger with movement, weaker with fixation.
What are the 5 key takeaways from Chapter 10?
