How does Warwick Schiller use the concept of the nervous system window for trailer loading?

Warwick Schiller uses the concept of what he sometimes calls the window of learning — the state of nervous system regulation where a horse can actually process information and make associations — as the central organizing principle of his trailer loading work. His position is that most trailer loading failures occur because the handler is trying to teach a horse that is operating outside this window, meaning the horse is too activated, too stressed, or too reactive to genuinely learn anything. Schiller's practical application involves reading the horse's body language for signs of whether it is inside or outside the window. A horse that is stiff, high-headed, blowing hard, sweating, tense in the jaw, or scanning the environment with a fixed eye is outside the window. A horse that blinks softly, has a lowered head, licks and chews, takes a deep breath, or shows any relaxation in the topline is inside the window. Schiller does his teaching only when the horse is inside the window. For trailer loading this means he might spend the first session doing nothing but standing with the horse at a distance where it is comfortable and waiting for it to come into the window. Once it does, he steps slightly closer to the trailer. If the horse goes back outside the window, he waits again. He never pushes forward while the horse is reactive. This approach can seem slow to observers but Schiller notes that horses trained this way often load on their own before he ever asks them to, simply because the trailer has become associated with calm rather than pressure. He also notes that handlers who work a reactive horse repeatedly — applying pressure, getting a partial response, applying more pressure — often create a horse that loads under duress but never genuinely accepts the trailer. The compliance looks like success but the horse is still stressed, and that stress eventually surfaces as resistance again.