Conditioned reinforcer

A stimulus that has acquired reinforcing value through pairing with a primary reinforcer (food, water, or another biologically rewarding stimulus).

The clicker in clicker training is the textbook example of a conditioned reinforcer. Out of the box, the click sound is neutral and has no inherent value to the horse. Through repeated pairing with food, the click becomes a signal that food is coming, and acquires its own reinforcing power. A trained horse will respond to the click with the same orientation and engagement they show toward the food itself, because the click reliably predicts the food.

Conditioned reinforcers are central to marker-based training because they solve the contiguity problem: the trainer can mark the exact moment of correct behaviour with the conditioned reinforcer, then deliver the primary reinforcer (food) afterwards without the operant link being weakened by the delay. Without a conditioned reinforcer, the trainer is limited to whatever behaviour the horse happens to be doing at the moment the food arrives, which in practice is usually whatever the horse did to approach the food.

The terms conditioned reinforcer and secondary reinforcer are used interchangeably in modern animal training. “Secondary reinforcer” is the older Skinnerian terminology; “conditioned reinforcer” is the term more common in current peer-reviewed work. Both refer to the same concept.

Conditioned reinforcers are not unique to formal training. Horses develop conditioned reinforcers naturally through their everyday environment: the sound of a feed bucket, the rattle of a halter, the approach of a particular handler. Any neutral stimulus that comes to reliably predict a primary reinforcer can become a conditioned reinforcer through ordinary classical conditioning.