The bridge is just a signal that is conditioned to be a positive secondary reinforcer because it is paired with primary reinforcers, usually food. Until it is paired with positive, primary reinforcers, it is not conditioned - that is, it has no significance to the animal when it is issued - it is just an incidental sound in the environment. It is very important to go through a training process to establish the meaning of the bridge signal. This can be done in 3 steps and a total of 7 trials. I use 'X,' or the spoken sound of the letter x as a bridge signal. More on why I chose this later.

Step One: Terminal Bridge: Present food treat while saying a short, crisp "X." Repeat this two more times for a total of three trials. This is the terminal bridge, used to tell the animal he has successfully fulfilled the trainer's request.

Step Two: Intermediate Bridge: Keep hand with food behind back and say "X." At the slightest response to the bridge(X) start a stream of x's, getting faster and louder as the animal approaches you to get food treat. You can also start to pull your hand from behind your back, finally presenting the food and a crisp, emphatic "X," as the animal reaches the food. So you have two kinds of bridge - the crisp, emphatic bridge which becomes the signal that the animal has been successful and may get a treat, and the softer stream of 'xxxxxxxxx' culminating in the crisp emphatic 'X.' These are the intermediate bridge, used to tell the animal he is not done yet, but he is headed for success.

Step Three: Testing: Before you go on to the next step, you need to make sure the animal understands the bridge. Wait till the animal is looking away (can get the help of a friend to provide a mild distraction). While the animal is facing away, say 'X.' If the animal turns immediately toward you in response to the sound of 'X' continue as in step two. You have been successful.

If the animal does not respond to the 'X' in the test, go back to step one and repeat.

Choosing a bridge: I have used whistles, clickers, flashing lights, visual gestures (a thumb up is one example), tactile signals, and verbal bridges. It does not matter which you prefer, as long as you use is appropriately and it has certain characteristics.

First, can the animal perceive it? A deaf animal would usually use tactile and visual bridges, because it cannot hear sounds. However, in general, trainers choose a sound bridge, because sound travels in all directions, versus visuals that can be obscured by obstacles, or tactile which requires being right next to the animal. The sound should be short, sharp, one syllable, not a word used a lot in conversation. It must be issued the instant the animal does what he has been asked to do. As long as these criteria are met, the bridge will be fine. If you do not meet these criteria, you are not being as effective or efficient as you could be.