I hadn't been paying any attention to this hread until a friend pointed it out. Interesting, that people have a variety of ideas as to why and when dogs bark?
Any dog owner can tell you that the dog can bark to play, bark to call attention to a threat, bark to call attention to itself, bark at toys, bark out of fear, bark to call out to another, there are a lot of reasons for a dog to bark.
Then you add drive theory and no one can agree as to what is going on? Then you add training and competition and you really have a mess.
But, if you go back to the beginning of training you can explain most things. Why does a schhIII yip bark in a blind? The yip can be identified with what basic behaviors? Play, prey (yes, dogs bark at or for prey...it is flushing behavior, sometimes learned sometimes genetic). The dog has learned to bark to flush its prey, in this case the man is the motor behind the prey or may even be the prey. In schhIII at the championships there has been huge amounts of training, the dog knows the game, so if the dog is doing bitework and has a genetic makeup of doing it in mostly prey and or prey and play, you will often get yippie barks.
If the dog does bitework from a higher amount of fighting instict it will present a broken deeper bark, it is challenging an adversary, one it knows it can defeat.
A dog working in defense will show a threatening very aggresive intense barking. A dog working even higher in defense may show hesitant barking (like hey I'm ready to leave but I've been trained to hang out here and it'll be OK).
There are many variations on the theme and virtually no dog at such a level displays only one area of these highly variable traits we so conveniently, and eroneously, package as "drives" as if they are precise totally defined packages of behaviors that the dog is either IN or not.
Of course many of us look at dogs at the SchHIII level and want to see how they bark at the man. It can tell us a lot about the dog. Ideally we see a strong and convincing bark at the blind, one that makes the helper transfix himself to the dog, not the other way around. A bark that tells the helpeer, hey I'm dangerous, move a muscle and I'll kick you butt, and the helper believes it. On the other hand we often see the dog looking at the booty, excitedly barking for action, the dog baiting the helper to move his prey item, no threat here just a continuation of a game.
We can also see some dogs that are soo high in defense that the challenge the helper also but it is to accomplish what has worked so well so often, and that is to keep the bad scary man away. Truly the sport pretty well eliminates the majority of such dogs and you won't see them at many trials. But keep in mind these dogs all fall along a continueum, there is not this type or that type, there are a vast number.
If you are looking at the dog, for what they were originally intended, and that is to be an appropriate behaving police or protection dog, I would look at the dog, that even while training repeatedly, still falls into that catagory of strong, confident, serious, in the blind. These are the very desireable dogs. A truly great dog will do this because he wants to, not becasue of a particular training style. Other dogs can go a variety of directions due to training style and some training styles don't work well on some dogs...for example, highly defensive helper work on a highly defensive dog more frequently that not will produce a very tenous dog in the blind, either the dog has to bump and bite, or leave.
just my two cents on an interesting subject.