The basic experiments on learned helplessness use two dogs, each in a separate room. In the control dog’s room, after a bell rings the dog gets a mild electrical shock — just enough to annoy and surprise him. This dog has a switch to turn off the shocks and quickly learns to use it.
The second dog is yoked to the first but has no bell and no switch. Every time the control dog gets a shock, it too gets a shock until the control dog flips its switch. So, objectively, both dogs get the exact same treatment, but the yoked dog has no ability to predict or control the shocks.
Next comes the test. Both dogs are put in a “shuttlebox” — a large box divided into two compartments by a low fence. From time to time a warning light comes on, and a few seconds later the floor of the shuttlebox emits a mild electrical shock. If the dog jumps from one compartment to the other, the shock is immediately terminated. Even better, if the dog jumps over the fence upon seeing the warning light, there’s no shock at all. As you might expect, the control dog quickly learns to jump over the fence on cue; though understandably a bit anxious, he’s relatively happy.
And the second, yoked dog? You might expect it would be just as motivated to escape the shocks in the shuttlebox. But this is where the results get very interesting, and somewhat depressing: The yoked dog just lies in the corner of its cage, whimpering.
The yoked dog learned in the experiment’s first stage that shocks happen unpredictably and inescapably — and it carried that mind-set into the shuttlebox. This dog learned to be helpless in its general approach to life, exhibiting symptoms similar to suffering chronic clinical depression.
(above taken from Dan Ariely's blog "Predictably / Irrational", 28th August 2008)