A study has been done comparing the effectiveness of various rewards in dog training. Stanley Coren talked about it in an article for Psychology Today.
I posted the following comment:
I find this research quite simplistic. First of all, a reward is not a thing, like a piece of food or a pat, and there’s no point in arguing about what is more effective. A reward is whatever the dog finds rewarding in that environment at that time. We know that some dogs in general are highly food-motivated, others are less so. Some are highly interested in toys, others are not. Some dogs will solicit patting while others will actively avoid it. For some dogs praise by voice, being a form of interaction, is a primary reward, but for many it is a secondary or not very reinforcing at all.
On top of all this, each dog will change according to the circumstances – for example what environment is the dog in? What range of activities and potential rewards are available? Food might be a good reward in an indoor training room but not in the park. Patting might be a good reward at home in the living room. And so on.
The there is the question of the value of the reward compared to the value of the behaviour being taught. For a highly socially bonded dog, being taken away from the handler might be difficult, and being allowed to come when called is rewarding in its own right, and might only need a small additional reward. Such a dog might need a stronger, higher value reward to reinforce staying, which requires tolerating separation from the handler. On the other hand, for a dog whose highest priority is sniffing the environment, and social bonding is low, coming when called would require a very high-value reward, and praise or patting would not do the job.
So in terms of the effectiveness of rewards, they are all relative. The best results are obtained by using a combination of rewards, and being aware of the dog’s hierarchy of preferences in each particular situation.
Then of course, the value of rewards can change as a result of the reinforcement history of different activities.
To really understand rewards, we have to study Premack. He tells us that the same activity can be both a reward and a punishment for the same dog under various conditions.