In the past trainers generally used a practice called "sacking out", which usually involved flooding a horse with so much frightening stimuli that the horse would experience something like an emotional overload and would stop responding to the stimuli. Repeated enough times, the horse would then learn the quickest way to make things less scary is to stop responding. Because this form of training was sometimes ignorantly carried out to such extremes that a horse would go stiff and practically catatonic whenever they felt fear, the method began to have a stigma attached to it and few people say that they "sack out" their horses nowadays. Since "sacking out" was "cruel" and "bad" a shift in terminology happened. Suddenly everyone was desensitizing their horses. Which is similar to "sacking out" in that it involves creating fearful stimuli and removing that stimulus when the horse stops reacting to it. Recently, though, I have seen a shift again. Horse lovers are now beginning to oppose the term desensitizing. Again, some of the bad feeling for the term comes from misuse of the technique. So, now, if desensitizing is bad too, what do we do to teach our horses not to freak out all the time?
A lot of this argument comes down to semantics. In some ways, I understand the aversion to the term desensitizing. I work very hard to have my horse sensitive to my cues and suggestions. I don't want my horse to simply stop responding when he is afraid. Until someone finds a reason to object, I will use the term: confidence building. The reason I like confidence building so much is because, in my mind at least, it encompasses so many techniques, including emotional flooding, if that is what my horse needs to help him overcome a fear. This is probably a good time to mention that my riding horse, Fargo, is the king of freaking out, and I have done a lot of confidence building with him using whatever techniques were necessary for the situation. Let me outline my method for confidence building.
Another way to build trust/confidence, besides just passively being friends, is introducing new things or potentially scary things, in a completely non-threatening way. If possible, I don't want to be associated with a scary object at first. For instance, if I want to get my horse accustomed to plastic sacks, I will have one in the area where we are playing, the moment I notice my horse has seen the sack, we immediately stop moving towards it. I will give my horse a couple small easy tasks on that spot and we will walk away from the sack. Then, we will turn around and approach again, I want the horse to be leading me, so that I don't accidentally drag them closer to the sack than they are comfortable with. When I see the horse hesitate, again we stop do a task, and retreat. I repeat this procedure until the horse has touched the sack on his own, without any influence from me. Only then will I pick up the sack, letting myself be associated with the scary thing. Using more retreat than approach I will continue to build the horse's trust in me and the sack until I can pet them all over with it or flap it around them.
Since I am still learning, there are times when I accidentally push a horse over the edge. I do a little too much approach, or keep doing something a little too long and the horse goes from being concerned to being very afraid. This is when desensitizing techniques are needed. If I retreat, or stop doing what scared the horse when he became frightened I will be teaching him to react with fear. Keeping the fearful stimulus going until the horse stops reacting is the quickest way to get them back to a state where they are confident enough to use retreat and re-approach again to build trust.
Sometimes trust is just not enough! When things get too scary or, like when working with a wild horse, human beings might be the frightening stimulus. Then using flooding (or "sacking out") techniques are needed. When I step into a pen with a wild horse for the first time, often that is all it takes for the horse to have an emotional overload! A mustang flooded with fear will often charge back and forth crashing against the fencing when I stand still in the pen. My biggest concern is not to add to the horse's fear when they are already flooded. It truly becomes a waiting game as the horse wrestles with its emotions. Similar to desensitizing, the moment I see the horse make improvement in gaining control of its fear I need to do what I can to reduce the cause of its fear. When the wild horse stops crashing back and forth I will turn my back on them or crouch down making myself smaller and less threatening. I repeat this until the horse has learned that the quickest way to make me less scary is to stop fighting/fleeing.
In summary, I am not against desensitizing a horse, but I think our ultimate goal should be building trust and friendship to the point that our horse tries to be confident about anything we ask it to do.