Licking/Chewing=Learning?

I'm studying for an MSc in Equine Science and am researching equine behavior. Having studied scientific literature, including your catalog of horse behavior (The Equid Ethogram, A Practical Field Guide to Horse Behavior), I cannot find any reports or descriptions of "licking and chewing" while head lowered in feral or domestic herds. My queries are as follows:

1. Do you know of any scientific reports describing or explaining that behavior?

2. Certain scientific authors are suggesting that this is "displacement behavior;" do you know of any studies that support this?

I've also experienced the situation when training a horse to do a new move--such as moving the right leg forward and back on command, as we stop and rest at each correct response. After being allowed to stand quietly for a short while, he will start blinking his eye, then move his jaw (his neck will usually be out front and to my eye does not look tense). I see it now with every horse I work with, and also observe it with other people working horses. I never noticed it until it was pointed out to me. It happens if you wait and give the horse time. This was described to me by a Canadian cowboy as "he's blinking so he's thinking, and now he's digesting the thought so he's now learned."

3. Can you help me describe this licking and chewing, blinking and jaw movement in scientific terms?

Isobel Duncan
Royal Dick Vet School University of Edinburgh


If I may be so bold, I noticed a behavior left out of your books. It is something natural horsemanship trainers have noted time and again. There is a "dawning" moment when the horse realizes this is what is being asked of him. That dawning moment is visibly seen by the horse licking his lips and chewing with the mouth slightly open or closed. (I don't think this is the popping and chewing of submissive behavior). I've heard it called "digesting a thought."

This behavior is often accompanied by an audible sigh and a much more relaxed posture, and the horse has learned. He/she now performs the requested behavior fairly reliably when asked in the same way.

Katrina Britner-Osborne
Burbank, Calif.


Isobel's questions and Katrina's comment concern a fairly common topic. In fact, there are a bunch of e-mails about horses "digesting thoughts" piling up in my desktop file of questions for this column. Thanks for the nudge.

The lowered head, relaxed posture, licking, and chewing are part of an autonomic response when stress or pain fluctuates, or when panic or startle resolve. The first scientific description I encountered was in the field of neurophysiology. In mammals, this cluster of responses occurs when the animal is returning from predominantly sympathetic tone (fight or flight response) back to parasympathetic tone (feed or breed response). This process is also known as sympathetic attenuation. So it is seen in all sorts of situations.

The textbook example of this relief after distress is that moment after the police's flashing light and siren whizzes on by without pulling you over. You might have a little itch on the scalp or neck, have to swallow, or exhale long and hard. A more dramatic driving scenario would be spinning out on ice, where your heart rate jumps, you break into a cold sweat, and have to pull over and hold your head in your hands before regaining focus.

These are the same signs in horses, to various degrees.

When a horse is suddenly frightened, then quiets down, the head drops, there might be salivation, tongue and jaw movements, and a sigh. It does occur in all horses, feral or domestic, whenever startled by something in the environment, or after a disturbance. In domestic horses, we see it most often when evaluating video of hospitalized horses in association with episode of pain, a minor seizure, or the collapse of narcolepsy. The scenario can be reliably provoked by presenting a startling noise, then letting things quiet down.

These behaviors also can be induced by administering drugs that produce the neurochemical conditions in the brain corresponding to anxiety and panic. Some have been studied in horses. At certain blood levels, panic followed by relief responses is seen. Rapid blinking and yawning, which are signs of the related autonomic state of mild anxiety, are seen at different blood levels. So these behaviors have always seemed very physiologic--plain and simple, no thought is required.

So in the popular demonstrations in which a horse is run around a pen, then allowed to stop--I think of the same simple underlying autonomic physiology. Scare or excite the horse, then stop.

Certainly, it could also be consistent with the more complex behavioral concept of displacement behavior. This term refers to behavior occurring out of context (usually feeding behavior) in a thwarted goal or conflicted situation. The horse is motivated to escape, but is thwarted from escape and the energy is redirected to feeding motivation, which induces salivation, chewing, etc. The jaw and tongue movements relieve the energy and so attenuate the stress.

The physiologist's and behaviorist's interpretations seem much more plausible than the submission, trust, "digesting a thought," or "dawning moment" you hear about in popular horse talk. That's why some people question whether the high-pressure aspect of some "natural horsemanship" techniques are the most humane. They would say that if the horse is thinking, it's likely "I'm scared, want to get out of here now," or "Thank goodness this guy has stopped chasing me in circles so I can relax for a minute."

Years ago we studied punishment in horse training. In that context, when subjects "figured out" how to avoid the punishment, they usually showed the lowered head, lip licking, chewing, and sighing. They then responded correctly and avoided punishment, so they had learned. But they usually showed signs of anxiety and mild depression. The end of a training trial seemed like relief, "Thank goodness that's over," and they became reluctant to do the trials.

In contrast, more recently we've been doing some cognition studies using all positive reinforcement. This involves basic operant conditioning trials designed to test the ability of horses to understand a concept in relation to discriminating between various olfactory, auditory, or visual stimuli, presented two at a time. When at first the horse accidentally made the correct response, it got a food reward. If the choice was incorrect, no treat, no punishment, we just went on to the next presentation.

Each horse reached an "Ah ha!" point where they seemed to "get it," after which they made nearly 100% correct choices. They seemed more eager in their anticipation of the next presentation and more enthusiastic in their response as if they could play the game all day. And their enthusiasm for learning seemed to stay with them.

Some individuals do go through a stage of apparent frustration when early--or by chance--they have a series of incorrect choices. They might paw and turn their head back away from the stimulus presentation board as if they want to leave. When those animals finally "get it," they might show some lip licking, jaw movements, and deep exhalation, but those signs are not as strong as the situations involving fear, pain, or punishment learning paradigms.

These differences in the "dawning moments" of the punishment vs. negative reinforcement vs. all-positive reinforcement learning models--with and without a period of frustration--are very interesting.

Katrina, you didn't mention the training method in your "dawning moment," but I guess it was primarily pressure and release (negative reinforcement) as opposed to positive reinforcement. I'm becoming convinced that study of the relative effectiveness of pressure and release methods vs. positive reinforcement-based training might lead to advances in horse science and more humane training methods.

About the Author

Sue McDonnell, PhD, Certified AAB

Sue M. McDonnell, PhD, is a certified applied animal behaviorist and the founding head of the equine behavior program at the University of Pennsylvania's School of Veterinary Medicine. She is also the author of numerous books and articles about horse behavior and management.

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