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Yes we can. This question was pretty well answered in the 1950s.

Note: You need a basic understanding of the processes (often called quadrants) of operant learning for the discussion in this post to be meaningful. You can read my post, Operant Learning Illustrated by Examples, to get the basics.

Lately I’ve been reading a lot of remarks that seek to minimize the difference between positive and negative reinforcement. Some people claim that you can’t determine which process is at work in any reinforcement scenario (continuum fallacy, anyone?), and it’s even been argued that the terms “positive” and “negative” should be abolished. More on that in a later post, but if you pick up any new edition of a learning theory textbook, guess what? That point of view may be mentioned but the terms are still in use.

I got curious about the food argument so I gathered up some articles I had and did a little poking around in the psych journals.

To review:

Positive reinforcement: Something is added after a behavior, which results in the behavior happening more often.

Negative reinforcement: Something is removed after a behavior, which results in the behavior happening more often.

Both processes increase behaviors, but most trainers feel there is a big difference between the two methods. Negative reinforcement involves an aversive (the thing that gets removed), and most trainers in the positive reinforcement oriented community want to avoid that. But there seems to be a growing minority that either truly doesn’t perceive a difference or is focused on some gray areas and generalizing from those.

Indeterminate Situations

There are indeed some situations where it is very difficult or impossible to determine the major process. The classic example is that of thermostat adjustment. If you are a little bit cold and go turn your thermostat up 2 degrees and the furnace comes on, are you adding heat or reducing cold? Most people would say the latter (negative reinforcement), but that heat can sure feel pleasurable and luxurious in its own right when it comes on. The situations that don’t fit well into one process or another generally have in common that they deal with a continuum of states and not discrete things that are added or removed.

So yeah, there are some scenarios where the primary process can’t easily be determined.

But food intake is not one of them.

Here’s how the argument is usually presented:

People who train with food are employing a negative reinforcement protocol because food removes the aversive state of hunger.

I have seen this claimed by force trainers but also a few people in the positive reinforcement (oops! maybe they wouldn’t call it that) community. It is often played like some sort of trump card, but it is as out of date as dominance theory.

What I haven’t seen is anybody pointing out is that there were multiple experiments performed in the 1950s that successfully separated out the positive reinforcement qualities of food that were independent of assuaging hunger. So here we go.

The Studies

In 1950 Sheffield and Roby published, “Reward value of a non-nutritive sweet taste.” The abstract from APA PsychNet:

After showing that hungry rats will ingest significantly more of a 1.3 gram/liter saccharine solution than satiated control animals, the hungry rats were trained on a single unit T-maze with a saccharine solution reward. Learning was rapid and showed a high positive relation between correct choice and speed on the one hand and rate of ingestion of the saccharine reward on the other. After discussing the implications of these results for various learning theories, the authors conclude by suggesting “that elicitation of the consummatory response appears to be a more critical primary reinforcing factor in instrumental learning than the drive reduction subsequently achieved.”

“Drive reduction” corresponds to negative reinforcement effects, the satiation of hunger in this case. They removed these effects by using a substance that had no nutritional value. The study showed that while the rats gained no calories, eating a tasty but nutritionally empty substance could be an effective reinforcer.

In 1952 Miller and Kessen published “Reward effects of food via stomach fistula compared with those of food via mouth.” Here is the abstract:

Rats prepared with stomach fistulas were trained in a simple T-maze under hunger motivation and with rewards of milk for correct choices and isotonic saline for incorrect choices. Different groups received milk in a dish or milk injected directly into the stomach. While both groups reduced errors and time significantly, the “milk-by-mouth” group learned more rapidly. “These results show that milk injected directly into the stomach serves as a reward to produce learning, but that milk taken normally by mouth serves as a stronger reward to produce faster learning.”

This says that even for an animal that is food deprived (“under hunger motivation”) there is a reinforcement effect beyond satiation of hunger. What’s left? Positive reinforcement. It’s not controversial to say that eating food is pleasurable. What’s interesting is that this experiment shows that it is pleasurable aside from satiation.

Makes Sense to Me

Actually, we know this intuitively. We have taste buds. Preferred foods taste good to us. It’s a major pleasure. How many of us will eat something we really like even after we are full? Some of us could easily do that three times a day!

I don’t know if all animals have taste buds, but most organisms must have a method for discriminating for appropriate foods. Doesn’t it make sense that organisms would have a survival advantage if they got immediate feedback about this, rather than having to wait until they have digested the food?

And it doesn’t take much observation to conclude that dogs enjoy food, does it?

There has been a lot of research on this topic and I have yet to find an experiment that had an opposing result. The same effects have been shown with water consumption and even sexual activity (Sheffield, Wullf, and Backer, 1951), both primary reinforcers. And a personal note: I don’t enjoy reading about these unfortunate experimental animals, whose lives were almost certainly short and painful. But since the knowledge has already been gained from the studies, the least we can do is pay attention to it.

So back to food. Even if your dog is extremely hungry and you expect that negative reinforcement will be involved if you use food to train, the studies say that there is also positive reinforcement even in that extreme situation. Taste buds probably don’t turn off when animals are famished.

There’s another aspect that I haven’t seen mentioned in a study but a smart FaceBook friend mentioned. Putting a treat in your mouth and getting pleasure from tasting and swallowing the food are perfectly and immediately correlated. But there is not a one to one correlation between each piece of food and a perceptible reduction in hunger. At least in humans, satiation is delayed. If you have a perfect meal in front of you with the exact volume of food and number of calories to fill you up, and you divide it up into 30 bites, your hunger is not assuaged 1/30th with every bite. The relationship is just not going to be that salient. The diminishment of hunger is probably delayed, and less linear. The positive reinforcement component would almost have to be stronger, which is what the studies with rats found.

Maximizing Positive Reinforcement

If you are still worried about a negative reinforcement component with training with food, it’s easy to address. To minimize (and possibly eliminate) the presence of negative reinforcement effects, how about this: don’t train your dog on an empty stomach. Meaning the dog’s stomach, silly! But it’d probably be good if you have eaten something too. You want to be at your best when training!

Use appropriate sized pieces of good treats and you can be fairly confident that you are training with virtually entirely positive reinforcement (if the behavior increases, of course). If calories are a concern, cut down the next meal. Also, recent research indicates that dogs, just like people, probably learn better when their stomachs are not empty. Makes me feel good that I have almost always given my dogs some of their meal ahead of time to take the edge off before training.

I’ll be writing more about the movement to eliminate the terms “positive” and “negative” from the technical descriptions of the processes of operant learning, and the nature of reinforcement in general. It’s a pretty interesting topic. In the meantime, you folks who are training with food: you can sleep well at night.

Thanks for reading!

Coming up:

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