Study of this area helped reveal how the bat knows when to start counting the delay. FM1 is suppressed by the bat so that it is just audible to the neurons of this area, but is too weak to generate an echo. The FM-FM Combination sensitive neurons are arranged in an array of systematically decreasing preferred delay. Dealys down to a few hundred microseconds can be measured by these neurons. In a larger or faster bat, this window is set much larger.
Single neurons can have extraordinary specificity for a patten of stimulation.
In the case of the mustached bat, it would have taken an infinity of time to discover the optimal stimulus for an FM-FM combination neuron had the natural echolocation sounds not been available as a clue. This problem is often cited by those who reject the notion of feature filtering, on the grounds that too many neurons would be required to cover all the possibilities. The flexibility probably exists in direct proportion to how far up the hierarchy they are, with hippocampal neurons having the greatest plasticity of all. Nearly everyone thinks that they may have separate functions, but the details of those functions are pretty elusive. In the case of the bat, we can have much confidence that each area has a separate function, because we can relate the properties of the area so directly to the function.