Perception Lecture Recording on March 4th 2025

Potency in Visual Processing

Discussion on different forms of potency in the lateral geniculate nucleus and primary visual cortex.
Importance of understanding receptive fields.

Concomitant cells respond to pairs of cones.
- Opposing cones: Red (l) or Green (m) vs. Blue (s).
- Receptive fields can have l or m in center or surround.

Center and surround roles vary:
- Examples include ‘m’ in center or surround.
- Identifying excitatory vs. inhibitory elements is essential in drawing correct receptive fields.

Maximally stimulated by uniform light.
- Specific neuron example:
  - Excited by green light (when m is excitatory in the center).
  - Inhibited by uniform red light.

Found in the primary visual cortex.
Opponency occurs in both center and surround:
- Green (excitatory) in center, inhibitory in surround.
- Red (inhibitory) in center, excitatory in surround.
Produces maximal firing for borders (edges) between colored regions (e.g. green and red).

Vergence: based on angle between two eyes while focusing.
Feedback from extraocular muscles helps the brain gauge eye angles:
- Larger angle when focusing on closer objects, uncrossing for distant objects.
Effectiveness diminishes beyond two meters; angle remains fixed.

Textured Gradient: From logs in an image; fine detail diminishes with distance.
Linear Perspective: Observed in aligned structures like ladders; lines converge with distance.
Relative Size: Objects (ladder rungs) appear smaller with distance.
Relative Height: Position of objects relative to an implied horizon.
Occlusion: When one object overlaps another, implying closeness.
Shading: Variances in light create depth perception.
Atmospheric Perspective: Distant objects appear hazier.

Neurons tuned for motion detection depend on their retinal positions.
Delays impact directionality of perceived motion:
- Direction determined by which receptive field is stimulated first.
- Speed of motion is inferred from the length of delay in circuits.

Two main types of eye movements:
- Saccades: Rapid-fire eye movements; vision suppressed during.
- Smooth Pursuit: Tracking a moving object smoothly; requires a moving subject to initiate.

Smooth pursuits can make stationary objects seem to move across the retina.
Need for extra-retinal information (like eye position) to determine true versus perceived motion.
Corollary discharge theory: duplicate commands sent to visual cortex for immediate adjustment based on eye movements.

Coordinates eye movement commands sent to the extraocular muscles and visual cortex.
Traveling info to both locations is believed to enhance motion perception.

Rare condition where individuals cannot perceive motion, even though they can see other things normally.
Can deduce motion through changes in static images over time.

Perceptions after extended uniform motion (e.g., waterfalls).
Opposite motion is perceived when stationary objects are viewed afterward due to fatigue of motion detectors.

Interaction between perception and action through context, such as reaching for a cup.
Action influences perception, emphasizing active nature of perception.

Key concept in understanding movement through environment.
Points move across the retina in relation to focus of expansion during movement.
- Closer objects move faster across retina.
Important for navigation (e.g., while driving or walking).
Changes in gaze influence how effectively we utilize optic flow.