📗 -> 04/21/25: NPB163-L7

Sensory Systems Slides

🎤 Vocab

❗ Unit and Larger Context

Started from “Mapping receptive fields (2)”, page 21

✒️ -> Scratch Notes

Simple Cells and Complex Cells

Simple Cells - Spatial Frequency tuning
Complex Cells - Orientation tuning, and movement

Mapping Receptive Fields (3):

White noise stimulus and reverse correlation
Find the most active random patterns for a neuron, and average them?

Get out almost a heatmap for the receptive field
However, the prior for this is that cells are independents.
- For complex cells that need relationships between cells, it won’t capture relationships

Neural Maps in V1

1. Retinotopic Maps

2. Orientation preference maps

Neurons with similar orientation preferenecs tend to be grouped together, and there tends to be a transition between preferences.

We see distinct pinwheel centers, where multiple preferences aggregate
Finds round pinwheel centers:
Preference orientation changed smoothly around pinwheel centers
Tuning width of neurons close to pinwheel center was slightly larger than those of neurons in iso-orientation domains (1 preference)
- 37 vs 31, slightly more general

3. Ocular Dominance Map (inputs to granular layer)

Columns of neurons more responsive to one eye, left vs right.
This dominance pattern does not arise in V2.

Visual Processing Beyond V1

Monkey Brain pic
Proposed functional roles:

Dorsal Pathways
- “Where” pathway
- Vision for action
Ventral Pathways
- “What” pathways
- Vision for perception

Human fMRI pic

Motion Processing

MT / MST

Neurons in area MT (middle temporal area; V5) respond selectively to visual motion and are direction tuned

Directional Selectivity can arise from differential delay of input signals:
to detect motion from a to e:

Stagger delays such that a has the longest delay, and e has the shortest delay
Only fire when the delayed spikes arrive all at once (due to the delays)

MST (medial superior temporal area) neurons respond to more complex motion patterns involving rotation and expansion/contraction

Counter/Clockwise rotation
Contracting in / out (think a parallax effect)

Motion processing

Perceived vs. local motion: Aperture problem
- Difficult to integrate motion without complete information?
- Review
  Barber pole illusion

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NPB163-L7