I’m trying to understand the difference between V1 and V3, or one region and another higher in the hierarchy. I’m looking for some sort of asymmetry, or is the hierarchy not reflected by connectivity? Is voting different from V1 to V3 than V3 to V1?
I think that thinking about scale in terms of hierarchy is an oversimplification. Two scales are like two different senses. For example, MT is specialized for motion in the visual world. That sort of requires its receptive fields to have a certain range of sizes. That’s true of a lot of sensory submodalities, even different types of cortical columns in the same region. Since voting integrates multiple scales of RFs and multiple senses, I don’t see why scale of receptive fields is different from other aspects of sensory input.
Some convoluted reasoning which I spent 8 months on suggests different types of cortical columns in the same region can exist at different levels of the hierarchy. That could mean scale = level in hierarchy even though scale depends on the submodality, multiple of which can exist in the same region. The reasoning would also mean a given level of the hierarchy doesn’t always include all layers of the cortex, which would be weird in its own way.
Convoluted Reasoning
I think the first level of a hierarchy in the whisker region of S1 lacks L2 and L6b.
In the barrel cortex, there are barrel columns and between them is the septal domain. In some layers or sublayers, such as L6b and L2, barrel structures round off and disappear before extending through the whole sublayer. It seems like the septal domain is higher in the hierarchy (defined by L5 → thalamus → L4/6) than the barrel columns. Either that, or any of a few papers are wrong and projections from L6a to the thalamus don’t follow an apparent rule.