What does Warwick Schiller say about horses that neck rein in the arena but fall apart on the trail?

A horse that neck reins reliably in the arena but becomes unresponsive or difficult to steer on the trail is demonstrating a context-specific conditioned response rather than a genuine understanding of the communication. Warwick Schiller's framework explains this clearly: the horse has learned to respond to the neck rein in the specific context of arena work, but has not generalized that learning to other environments. Schiller's explanation draws on his understanding of how horses learn in context. If all neck rein training has happened in the same arena, on the same footing, with the same sensory environment, the horse's response becomes linked to that context as much as to the rein cue itself. On the trail, where the sensory environment is entirely different — different footing, different smells, different visual stimulation, different sounds — the horse's nervous system is more activated, its attention is on the environment rather than on the rider, and the conditioned response to the neck rein is partially or completely inaccessible. His solution is deliberate generalization training: taking the neck rein work to many different environments, including trail situations, before the horse's trail behavior becomes problematic. A horse that has been neck reined in many different places has a more robust, context-independent response to the cue than one trained exclusively in one location. He also addresses the activation component specifically: a horse that is too stimulated by the trail environment to respond to the neck rein needs its nervous system addressed before its steering does. Asking for soft flexion, walking in serpentines, or simply allowing the horse to stand and process the environment until it settles — the same principles he applies everywhere — will bring the horse back into a state where its training is accessible, including the neck rein.