In point of fact the three actions of perceiving, determining, and responding were sequential; but so infinitesimal were the intervals of time between them that they appeared simultaneous.
When you have two of these questions like this, it's best to use two different paragraphs just to make sure that everything is organized and that you're getting points in your coherence and cohesion.
Because this historical language was never written down, we can only reconstruct by comparing its descendants which is possible thanks to the consistency of the changes.