Fig 9. Refinement of receptive fields with 2D plane waves.

A. Refinement depends on the direction of wave propagation. If an initial RF is circular (left), then waves traveling along a horizontal direction will refine the RF along the horizontal axis only (top row). The RF necessarily expands to the arbor boundary along the orthogonal axis. Likewise, waves traveling along a vertical direction refine RFs along the vertical axis only (bottom row). Increasing time from left to right. Arrows: direction of wave propagation. Solid teal circle: arbor boundary. Dashed green circle: boundary of the initial RF. B. Final RFs that were exposed to plane waves traveling randomly in 16 possible directions. Left: using the same wave speed (4 mm/s) and STDP parameters (τ ₊ = 20 ms, A ₋ = 0.55) as in A. Centre: using a slower wave speed (3 mm/s) to lower the characteristic spatial frequency of κ(x). Right: using the faster wave speed (4 mm/s) but shifting refinement phase space to lower frequencies by increasing the bias for synaptic weakening (A ₋ = 0.60). C. Summary of the development of RF sizes for each of the conditions in B, averaged over three trials for each condition.