Masters Thesis Part 2: Receptive Field Theory

So how did I go about creating a model capable of predicting individual neuron responses of primates to various patterns of moving white dots? The key was to use receptive field (RF) theory. In general, a RF is a physiological construct associated with an area of the visual field. Let's say you're staring straight ahead and perceive some motion across the upper right of your visual field. You may have a RF associated with that region such that as you perceive motion across it your nervous system reacts by speeding up (excitation) or slowing down (inhibition) the number of electric impulses between neurons in your visual cortex within a certain period of time.

Each RF is very simple in structure. Imagine a doughnut. The outer ring and missing center form 2 separate areas across which the RF responds to motion. There are 2 flavors of RFs. The first is on-center off-surround where motion across the center causes an excitatory response and motion across the ring causes an inhibitory response. The second is off-center on-surround, which behaves in the opposite way. Multiple RFs can be aligned in various ways to respond to various directions of motion. If you consider your visual field to be 2-D with an x-axis (left/right) and y-axis (up/down), you can place multiple RFs within that plane to respond to all kinds of motion.

An extension of the RF theory is that each RF has a directional preference. This makes sense if you think about how multiple simple on-center off-surround RFs and off-center on-surround RFs can be combined to form more complex RFs. With the addition of a directional preference, the 2-D visual field space becomes a 3-D RF space. The task then becomes a matter of placing RFs within the RF space, aligning them properly, sizing them properly, and understanding the relationships between them.

Read the full report (PDF) for a complete explanation.