Tertiary reinforcers are defined in the literature as a type of conditioned reinforcer. The designation of “tertiary” is an indication of how many stimuli separate it from the primary reinforcer: a tertiary reinforcer is followed by a secondary reinforcer that is followed by a primary reinforcer (Bostow & Tompkins, 1999). A commonly used example of a tertiary reinforce is a poker chip, because it is reinforced by money (a secondary reinforcer), which is reinforced by food, drink, or other human needs (a primary reinforcers).

There is a debate among skilled trainers as to whether this type of KGS is necessary. Some suggest that when behaviors are approximated to duration properly, a KGS is not needed. Others argue that if a KGS has been previously conditioned as a reinforcer, its use can speed up the training of duration behaviors. I have not found the need to use a KGS, but I have observed situations where it appears to accelerate training. Because I have seen it work, I am hesitant to discount it as a viable tool without further data.

The second common use of the KGS is as a cue to guide or direct animals from place to place—when an animal is trained to move in a specific direction as long as a tone is played (the KGS), for example. When the trainer switches off the tone, the animal stops forward motion and begins changing its behavior (turning its head in various directions) until it hears the tone again. When the animal “finds” the tone, it moves forward again, in the direction it is facing when the tone resumes.

This type of KGS is used in certain military applications to guide an animal from location to location, even when the animal has never been in those locations before. This use of the KGS is a sophisticated cuing tool and it is very different from the other type of KGS described above. Yet, it is clear why those who use it call it a Keep Going Signal—it signals to the animal quite literally to keep going.