W4 - Motion Flashcards
Does the retina and LGN detect motion?
No, the retina and lateral geniculate nucleus (LGN) do not contain motion-sensitive cells. Motion is processed in a hierarchical pathway in the brain.
What roles do V1 and V2 play in motion processing?
V1 and V2 detect basic motion, such as left-right motion and simple stimuli. They are not highly specialized for motion.
What happens to motion perception if V1 is damaged?
Damage to V1 causes blindsight, but motion can still be sensed due to direct LGN → V5/MT projections.
What type of motion does V3 (VP, V3B, V3A) process?
V3 processes motion of complex textures.
What is the main role of V5/MT in motion processing?
V5/MT handles the bulk of motion processing, with large receptive fields tuned for direction and speed and even responds to static images that imply motion.
What kind of motion does the MST (Medial Superior Temporal area) process?
MST processes complex motion patterns like locomotion, expansion, and contraction.
What does area V6 specialize in?
V6 responds to self-induced motion.
How does the brain perceive motion differently when an object moves on the retina vs. when the retina moves with the object?
If an object moves across the retina while the eyes remain still → Perceived as motion. If the eyes track a moving object, causing the image to remain stationary on the retina → Still perceived as motion because the brain accounts for eye movements.
What mechanism allows the brain to correct for self-induced motion?
Corollary discharge signals (or efference copies) help the brain distinguish between motion caused by eye movements and actual object motion in the environment.
What is Sherrington’s Inflow Theory, and what evidence supports it?
Inflow Theory states that the brain detects motion based on sensory feedback from the eye muscles. Evidence: If you move your eye voluntarily, your vision remains stable because the brain accounts for muscle contractions.
What is Helmholtz’s Outflow Theory, and what evidence supports it?
Outflow Theory suggests that the brain predicts motion using the intention to move the eyes rather than waiting for muscle feedback. Evidence: If you poke your eye (causing movement without brain-generated intent), the world appears to move, proving that intention signals are critical for stable perception.
Which theory (Sherrington’s or Helmholtz’s) is considered correct?
Helmholtz’s Outflow Theory is correct because motion perception relies on the brain’s intention to move rather than muscle feedback.
How does the brain detect motion from sequential activation of receptive fields?
The brain combines signals from two points in time. A time delay is introduced to the first signal (A) so that it coincides with the second signal (B), allowing motion detection.
What is opponent motion detection, and where does it occur?
Opponent motion detection occurs in V5/MT (Middle Temporal area), where neurons respond preferentially to motion in a specific direction. The perception of motion is determined by the balance of signals from neurons responding to opposite directions.
What is apparent motion, and how does the brain perceive it?
Apparent motion occurs when an object appears at point A (time 1) and point B (time 2) without passing through the space in between. The brain assumes motion has occurred based on the temporal and spatial relationship of the stimuli.
What are the key factors that influence the perception of apparent motion?
- Time delay – If the delay between stimuli is too long, motion is not perceived. 2. Distance between A & B – If the distance is too great, the object appears displaced rather than moving.
How do movies and TV exploit apparent motion?
Movies refresh images every ~40ms to create the illusion of continuous motion from static images. TV screens update images in two sets of strips every 20ms to prevent flickering. High-frame-rate TVs (e.g., 120Hz) reduce motion blur but still struggle with very rapid movement.
What is the wagon wheel illusion, and why does it happen?
The wagon wheel illusion occurs when a spinning wheel appears to move backward in movies or under artificial light. This happens because the frame rate interacts with the wheel’s rotation speed, leading the brain to misinterpret motion.
Why does the wagon wheel illusion become stronger at faster speeds?
When a wheel moves slowly, small displacements between frames are easy to interpret as forward motion. When a wheel moves faster, the displacement between frames is larger, making it easier for the brain to misinterpret motion as moving in the opposite direction. If the wheel moves in perfect increments (e.g., 90-degree rotations per frame), it may appear motionless.
When does motion sensitivity develop in infants?
6-8 weeks – Infants can track motion but cannot distinguish direction well. 10-12 weeks – Motion sensitivity develops significantly. 6-14 weeks – Rapid improvement in motion perception.
What type of motion is detected earliest in development?
Looming stimuli (objects approaching the viewer) are detected very early, possibly at birth, as they signal potential collisions.
Can developmental motion blindness occur?
No, there are no reported cases of developmental motion blindness. Some early motion abilities may be lost and need to be re-learned.
What causes motion blindness (akinetopsia)?
Damage to V5/MT (Middle Temporal area) leads to motion blindness, causing affected individuals to perceive the world as a series of still images rather than continuous motion.
What was observed in experiments with motion-blind patients?
Patients with akinetopsia could only perceive motion if 100% of the dots in a motion coherence test moved together. Even at 80% coherence, they struggled to detect motion. Similar findings were observed in monkeys.
