First, it isn't true that learning things in just one location is best for people - say, a desk set up for quiet study. Apparently moving to different locations improves learning - the theory is that, in part, this avoids the learning being linked to the specifics of the location. This is very similar to working with a horse on an exercise - say lateral work - and always doing it in the same end of the ring, or using only the long sides, etc. As I work with a horse, I always move to different locations in the ring as we work on a single exercise to generalize the learning, and if possible, repeat the exercise in other locations - say on the grass field or on the trail. I think this concept is one reason why horses sometimes "lose their training" when in a different environment - it isn't just distraction or excitement, it's that the horse has learned to do x movement in y place, rather than learning how to do x movement in itself. The neurology is a bit more complicated than that - it's that the horse (or human) learns to associate the task with a number of different sensations attached to a number of different settings, and that this strengthens the learning of the task that's the primary objective.
Second, a particular thing is learned better when it's incorporated into a work session that contains multiple exercises focussing on somewhat different tasks. I usually have several objectives for a work session and alternate working on one task, and then another, and often a third, in brief, intense sets. Apparently switching between tasks, as opposed to drilling a single task, improves learning and retention.
Third, gradual learning - where a task is learned one day, then reviewed/relearned the next session, and so on, produces learning that is retained better. Breaking the learning down into multiple sessions over a number of days is much more effective than working on only one task intensively for a long time. In fact, the forgetting, partial or complete, actually helps learning in the long term, because the repeated relearning/reinforcement cements the learning. So if your horse comes into a second work session on a task, and seems to have forgotten part of what he learned the day before, that may actually be a good thing in the long run!
So, for better learning - in horses or humans - change up the environment, mix up the content and space out the sessions. Very interesting stuff!