Research Bites Podcast

#37: Sensitization vs. Habituation: What Every Trainer Needs to Know

• Kristina Spaulding, PhD, CAAB • Episode 37

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 In this episode of the Research Bites Podcast, Dr. Kristina Spaulding dives deep into two foundational—but often under-discussed—forms of non-associative learning: sensitization and habituation. Drawing on research and classic learning theory, she explains what these processes are, how they differ, why they matter, and how they show up every day in companion animals. 

Dr. Spaulding connects the research to practical strategies you can use right away. From monitoring behavior and adjusting stimulus intensity to incorporating conditioning and systematic desensitization, this episode offers clear guidance for helping animals move toward calmer, more adaptive responses.  This episode will help you learn how to apply these principles thoughtfully in real-world training and behavior work. 

Whether you're a trainer, behavior consultant, or simply passionate about science-informed practice, this episode will deepen your understanding of how animals learn—and how you can support them more effectively.

For more information, please check out my website and social media links below!

[00:00:00] 

Hello and welcome. I'm Dr. Kristina Spalding, and this is the Research Bites Podcast brought to you by Science Matters Academy of Animal Behavior. We foster conversations about science and its application to animal training and behavior. In an effort to improve wellbeing for animals and the people they live with, please enjoy geeking out about the science of behavior.

Speaker 2: If you're like me, you want to stay current on the science of dog behavior, but who has the time to dig through the academic journals when your calendar is packed with client sessions and you're focused on growing your skills and training methods, learning theory and behavior. That's why I created Research Bites, a monthly subscription for dog professionals at any stage of their journey who want to learn, grow, and stay connected to the [00:01:00] science.

Each month I break down a cutting edge research study highlighting the key takeaways and showing you how it applies to real world training and behavior work. We meet live to discuss the study in more depth, and if you can't attend, it's okay. Every session is recorded. There are also multiple opportunities each month to join me and others for live conversations focused on applying research to practice.

Whether you're brand new to the field or have decades of experience, research Bites is here to help you stay informed, engaged, and part of a supportive learning community. Head on over to www.sciencemattersllc.com or grab the link in the show notes. Use the code RB podcast to get 50% off your first month.

I'll save you a seat.

Speaker: Today I'm gonna talk about a less commonly discussed area of learning that I still think is very important, and that is a sensitization and [00:02:00] habitation. So the first thing that I want to do is I wanna give you several definitions of these topics as well as other terms that are closely related to them.

When I was teaching learning in graduate school to undergraduates, the textbook that I used. Learning and memory from Brain to Behavior by Gluck, Mercado, and Myers. And that is what I'm drawing much of my information from today. If you ever want a good textbook on learning and memory, I highly recommend this one.

The most recent edition is the fourth edition from 2020, but you can still find a lot of useful information in older editions. Okay. So let's move on to our definitions. I'm gonna start by defining learning, and again, this is the definition of learning used by GL Mercado and Myers, and they state that learning is a change in behavior [00:03:00] due to experience.

I like this definition of learning. It's clear cut, it's simple, and it works. The next definition to know is non associative learning. And this is the category that sensitization and fall under, and this is the simplest form of learning. It happens when. A change in behavior occurs simply due to repeated exposure to a stimulus.

In this case, the stimulus is not being associated with a consequence like reinforcement or punishment, and it's not being associated with another stimulus. So again, the fact that. The learning is occurring simply due to repeated exposure, and that's why it's called non associative learning. I'm gonna start off by defining both habituation and sensitization together, and then we'll talk about each one of them separately, and they're pretty straightforward to define.[00:04:00] 

Refers to a decrease in the strength or frequency of a response to a stimulus simply due to repeated exposure. And sensitization refers to an increase in the strength or frequency or frequency of a response to an arousing stimulus after exposure. And we'll talk more about that in a little bit. So in habitation you see a decrease in the strength of frequency of a response, and in sensitization you see an increase in the frequency or strength of a response.

And both of these are forms of non-associated learning. When we are thinking about sensitization and habitation and working with companion animals or any other kind of animal, one of the biggest concerns for us is sensitization, right? Because sensitization can learn to fear, which can then. Kinds of additional problems for that animal.

And so we don't really want our animals becoming [00:05:00] sensitized to stimuli in the environment can be a problem too, but it's probably not something that comes up that often in. Companion animals. It is something that is talked about in wildlife management because, for example, we don't want wild animals habituating to things like cars because then they're not fearful of them and they may be more likely to be hit.

But for the purposes of most of the listeners. Who are very likely working with companion animals or at least captive animals. Our biggest concern is sensitization. One of the things that is important to us is how likely is the animal to sensitize versus habituate to a stimulus? And this is not an easy question to answer.

It's not always clear cut, and we cannot always predict this however. As I go through this podcast today I hope to give [00:06:00] you a variety of different pieces of information that help you predict this and also help you understand how to work with this type of learning and predict what's likely to happen with an animal on different situations.

So let's start with habituation, which in most cases is going to be what we would prefer to happen, right? We want the animals respond to decrease in strength and or frequency over time. actually there may be situations right where, especially with working dogs where we don't want them to habituate.

So scent work would be an example, right? I don't know how much this is an issue that comes up, but you don't want the animal to get. To the scent, and therefore show a decrease in the response to that scent. so when does habitation happen? It'll happen faster. If the stimulus is less arousing, that is less exciting.[00:07:00] 

So stimuli that cause more emotional or physiological arousal in the animal. Are either be less likely to habituate or at least it'll take longer. if we're ever in a situation where we're trying to get an animal used to a stimulus, we wanna start with less exciting stimuli and very closely related to that.

Animals are habit. The stimulus is weaker and often weaker are also gonna be less arousing. And so those two things are gonna together very often. And then if now this is where things get a little bit tricky, so. Habitation will also happen faster if there is less time between exposures to a stimulus.

However, if there is less time between exposure to a stimulus, you also tend to get a stronger spontaneous recovery. So spontaneous recovery is what happens. So let's [00:08:00] say that an animal is being exposed to a beeping sound and that beeping sound is played. Multiple times in quick succession, so that is going to lead to faster habituation.

However, if the animal is then not exposed to that beep for some period of time, what you tend to get is an increase in the strength of the response when they do hear that beep again, and we'll talk a little bit more in a moment about what lengths of time we're talking about, but for now, I'm just going to say.

Of time. So the animal habituates to a stimulus then does not hear the stimulus for a period of time, then they're exposed to it again. You tend to see a stronger response, and that is called spontaneous recovery. So if your goal, and I'm not saying, I mean there are, there are risks to trying to habituate an [00:09:00] animal to stimuli.

So that is something that definitely needs to be considered. However, there are also risks to exposing animals to stimuli where they haven't been habituated, because then we might see sensitization to happen or more likely to happen. I'll talk a little bit about this at the end of the podcast, but for right now, I just wanna go over the science of how it works.

So if the goal is to have faster habituation, then you wanna have less time between exposures to the stimulus. So you want them to be presented fairly close to each other. However, if you want the habituation to last longer, then you actually want to have more time between the exposures, so there's a trade off there If they're presented rapidly, if you're gonna get habituation, the habituation will happen more quickly, but then you get more of a return of the response after a break.

You space out the stimulus across longer [00:10:00] periods of time, or there's more time in between exposures to the stimulus. It will take longer to see habituation, but then it doesn't tend to return as strongly after a break. It doesn't mean it won't come back at all, but you don't. See as much of a recovery of that response.

So when we are talking about habituation, what you will see is when you put an animal through a session where you're repeatedly exposing them to a stimulus, and I'm just gonna say a tone 'cause I just think that's a little bit easier to get our head around. But it doesn't have to be a, a tone. It doesn't even have to be a sound.

There's other kinds of stimuli. Right. But I'm gonna use. Tone as my example. So you're exposing anal to a tone. Within that session, you are likely to see habituation, but you could also see habitation across sessions, right? So within a particular session, you would expect to see a decrease in [00:11:00] responding, but across sessions you'll also see a decrease in responding.

With the caveats that I just mentioned about spontaneous recovery, so you can kind of think of that. We have, let's say we have our responses at 100 and the animal goes through a session of habitation and maybe the response goes down to 50 and making these numbers up. They're kind of arbitrary, but it gives you something concrete to get your head around.

And then we have a break in between sessions where the animal's not exposed to the tone at all. And then they come back for the second session after some period of time. And now the responding iss at 75 again. Right? So we have had spontaneous recovery after a period of habituation, even when we start a new session and there's been some spontaneous recovery, it's not necessarily going back up to 100.

So that's what I mean when you can have habitation within a session where it [00:12:00] drops from 100 to 50, but also across sessions where in this example it dropped from 100 to 75. Another thing that's important to understand about habitation is that. The biggest decreases in response happen in the early stages of exposure to the stimulus.

And so in our example, we're talking about a tone, and this is very important because what this tells us is that if the animal is being exposed to the tone multiple times and you're not seeing a decreased response right away, that is a warning signal. Okay? That is a sign. That they may not habituate to this stimulus, in this example atone.

And that we may need to do something so that they don't start to sensitize to that stimulus, and that doesn't lead to problems down the road. an animal is being exposed to this stimulus, and this could be anything, right? It could be [00:13:00] tucked, it could be a sound, it could be a movement, if they're not habituating relatively quickly.

If you're not seeing any signs of a decreased response after the first two or three exposures, then I would say we wanna pivot because we are now at risk of seeing sensitization, and this may not be something you're intentionally exposing the animal to. Right, right. It might be something that's just naturally in the environment.

They have a reaction to a sound or again, what, sorry. Whatever the stimulus is, they have a response to a stimulus and then the stimulus occurs again, and you're not seeing a decrease in the response. Then we wanna step in. Now, we really don't wanna wait and see what happens because habitation is not likely to or because most of the habituation is going to happen after the first several exposures.

Now, one caveat I wanna make about this, [00:14:00] right? If the response that the animal is having is relatively weak, then the fact that it's not decreasing may not be that big a, a concern. As long as it's not increasing, right? But if the animal is having a moderate to strong negative response to something and they've been exposed to stimulus a few times and you're not seeing a decrease in that moderate to strong response, that's when we wanna interview.

So now let's talk about how long habitation lasts. So one thing, one thing that I think is not always translated into the real world from science. A lot of this research is done on phenomena that are pretty short-lived habituation. Typically, when we're talking about habituation in the lab, usually lasts for minutes or maybe hours or sometimes days.

That would be less common, but it's not permanent, and I think this is really important to understand. So I think a lot of the time we think that once an [00:15:00] animal has habit to a.

We're good and they're not gonna have a response again in the future. However, if they're not exposed to a stimulus for a while, that response will generally return. This again is the spontaneous recovery that I'm talking about. But when we're having longer periods of time, you tend to see more spontaneous recovery.

And how much this matters, again, is gonna depend a lot on what kind of response the animal is having. if their initial response right, is that they turn their head and they look, oh, what was that? And then they very quickly go back to what they're doing. We probably don't have to particularly worry about that response.

Unless we're seeing signs of an increased response. But if their initial response is to panic or attempt to flee or have a, you know, some kind of strong, again, moderate to strong [00:16:00] response, then we do need to be careful. And even if we see that response decrease after multiple exposures, it's really important that we understand.

That if the animal's not exposed to that thing for some time, they may have a stronger response in the future. So you can think about this, for example, in terms of dogs getting used to strangers, visitors coming to the home. They may take some time to what we would call warm up to that stranger, but this could also be the process of habituation.

Now as soon as you do something like adding food into the picture. We're no longer talking about habituation because we're now associating the presence of that person with something else, which means we've now moved into the realm of associative learning where the animal associating the person with something else, food or reinforcement.

However, if the [00:17:00] person is just coming over to the house and hanging out and the dog is getting more and more comfortable. And gradually we'll interact with the person and things are going well. The dog may get very comfortable with the person on that visit, but then as many of us know when that person returns, you're gonna see very often an increase in response.

And so it's just very important to be aware that this is a natural and normal thing that happens. So that we can plan for it. At the same time. It's often the case that in subsequent exposures, so after that initials exposure when some habituation occurs, then in the future when the animal exposed to that stimulus, habitation often occur more quickly.

Right? So again, to use the same example of a visitor coming over to the home on the first visit. Maybe it takes an hour for the dog to become comfortable, and of course, it would take much, much longer than that, but this is the example that I'm [00:18:00] using. Then the person leaves for a week and then comes back again and the dog has a strong response again, but maybe this time it only takes 45 minutes for the dog to become more comfortable.

And so the, the more we repeat this, the faster that habit is likely to occur. But again, remember that sometimes sensitization occurs instead, and we'll talk about that as well. So two more things that I wanna say about habitation. One is that habitation often does not generalize. So an animal may habituate to one sound and then show a strong response to a different sound.

And this is actually also how we know that. The decrease in responding is not just due to fatigue because you can expose an animal to a particular stimulus over and over again, and they'll get comfortable with [00:19:00] that stimulus and then. I don't know if I should say get comfortable. That's maybe implying some things that are going on that are not necessarily going on, but their response to that stimulus will decrease.

And then you expose them to a different stimulus and then you may get a very strong response again. So then we know it's not that the responding has decreased, just 'cause the animal is tired, that the habituation is actually happening. And then the last thing that I wanna talk about is a term that we really don't.

Much in the field, but it is out there. And is the term dis habituation? Dis habituation occurs when an animal habituates to a stimulus and then they're exposed to a different novel stimulus, and now their response to the initial stimulus increases. So let's go back to our human visitor example. So let's say you have a visitor come over named Bob and the dog [00:20:00] habituates to Bob and is showing decreased response, and you have a new person, we'll call him, Charles, come in, and now the dog has a strong response to Charles and is responding more strongly to Bob, even though Bob hasn't actually done anything or changed in any way.

If you see something like that happen. That is called dis habituation, and it does not take much for dis habituation to occur. So this may be an even more relevant example, is that one example is that adding motion can cause dis habituation, right? So we have our person come in, Bob comes in, and he sits on the couch and the dog is, you know, safely secured and just getting comfortable with Bob and again.

In many cases, we're going to have other things going on here, like adding in food, but I'm not using that in this example because that would make it [00:21:00] associative learning. So I'm not recommending necessarily doing this without food, but I mean, there may be some cases where that's appropriate, but the only reason I'm not talking about it is because that would make it a different kind of learning.

So Bob comes in everyone's hanging out and being calm, and Bob is sitting on the couch. not moving because he's been instructed not to move by the behavior consultant and the dog has relaxed and is no longer showing a response or a very strong response to Bob. And then Bob does something right.

He sneezes or he moves his arm, or you know, he stands up. And now we have this very strong response to Bob. Probably part of what's going on there is dis habituation. It's probably also more threatening, right, to do something like sneeze or move suddenly, or make a lot of noise. But there's also probably some aspect of dis habituation.

Another example is that you could have an animal habituate to a sound, and then they're exposed to a [00:22:00] different sound that causes a response. And now they're responding to that original sound again. So that is habitation and dis habituation. Next I'm gonna talk about sensitization. And again, this is simply an increase in the strength or frequency of a response to an arousing stimulus after exposure.

And so I think it's interesting that they use this definition again as coming from the the gl. Me and my textbook. And I think it's interesting that they use, that they add arousing in here, or maybe what I said, I think should say is that I think it's significant that they add arousing in here because if a stimulus is not arousing or exciting to an animal, then they're not very likely to sensitize to it.

It has to have, and I say exciting, but arousing really is a better word because. Can refer to emotional excitement. It can also refer to a physiological [00:23:00] response. And because we work with behavior. We're typically thinking of behavioral responses, but sensitization can happen in other ways. You can become sensitized to exposure to a chemical or to a food, for example.

So with sensitization, sensitization can occur after a single exposure to a stimulus. Particularly if that stimulus is very intense. I mean, that's typically when you would see this happen. Otherwise, it typically takes multiple exposures for sensitization to occur and like habituation, it is often, or it can be temporary and shortlived like minutes to hours but it can be longer lasting as well.

this is one of those areas where we just don't have enough of an understanding that we can make good predictions about, first of all, will this animal sensitized or not? There's a few things that can give us clues, but also how long will that [00:24:00] sensitization last? It is hard to say however.

Typically sensitization requires less exposure than habitation. So this brings us back to the fact that if an animal is gonna habituate to a stimulus, it's typically gonna happen. Well, you're gonna get bigger decreases in the response of the behavior early on. So again, if you are not seeing that, then your radar should be going off and saying, okay.

We may need to be concerned about sensitization here, and we may need to be proactive about trying to prevent that, right? Because it doesn't take as long to sensitize typically then to habituate. So we wanna be very quick about getting in there and intervening and avoid taking a wait and see approach.

Another way that sensitization is different from habitation. Is that [00:25:00] sensitization is not stimulus specific. So remember I said that habituation doesn't often generalize very well. Sensitization doesn't always generalize, but it can. And again, I wish I had more concrete answers for you here, but we just don't at this point.

If you want a broader discussion of sensitization and when it does and does not generalize, I recommend listening. On the physiology of the stress response, because I get into a lot more detail about that there. Here, all I'm gonna say is that you can have what's called homo sensitization, which is referring to.

An increase in responding to a stimulus after exposure to that same stimulus that's homo. So again, that just means that basically have one stimulus involved. You can [00:26:00] also Getty sensitization, which is when exposure to an initial stimulus causes an increased response to a different stimulus. This can also be called cross sensitization.

And so it's just important to understand that this can happen, right? If the animal is showing an increased response to a tone, then they may be more likely to show an increased response to some movement or a different tone. That would be that cross sensitization or thatty response. If the stimulus is strong, you are more likely to get a stronger response to subsequent stimuli.

And this fits in to what I was saying about habituation earlier, is that habituation happens faster when the stimulus is weaker, right? And so this is one of the things that can predict whether or not sensitization is going to happen versus [00:27:00] habitation is how strong is the stimulus? Stronger stimuli are more likely to sensitize.

Weaker stimuli are more likely to habituate, and it also depends on the arousal of the animal, right? So stimuli that cause strong arousal in the animal are more likely to sensitize and stimuli that don't cause strong arousal in the animal are more likely to habituate. None of this is guaranteed. But those are the two things that we can use to help us try to predict what is likely to happen.

And then similar to habituation and this habituation, we can also have desensitization. This is when an animal has become sensitized to a stimulus, but then. Their strength of their response starts to decrease over time. And so this might be, again, like maybe now we're presenting at a weaker level, and so it's not at the intensity of the stimulus is not [00:28:00] strong enough to induce that high arousal response.

And so you might start to see some desensitization. This sounds like it's very similar to habitation and behaviorally. It'll often look the same. But it is a, we know it's a different process because it looks different in the brain. So a couple other things that I wanna mention before we start to wrap up here.

Research by Dom John, that's D-O-M-J-A-N. In 1997, sorry, 1977, that animals would so showed that stimuli that would normally lead to habituation. Would cause sensitization if the animal was sick. So again, this is very important because it suggests that the animal is sick or presumably otherwise unwell or in pain.

Also, probably under stress. I mean, we know, [00:29:00] yes, stress can also make them more susceptible to subsidization that. Any of those things that are going on may also make an animal more likely to become sensitized. So now we have factors that increase the risk or the likelihood of sensitization are the strength of the stimulus.

Stronger, more intense stimuli are more likely to cause sensitization, the level of arousal in the animal's response. The stimulus, so stronger arousal on the animal is more likely to lead to sensitization, and then the current wellbeing of the animals. So animals that are somehow under stress, either psychological or physical stress through illness or presumably pain, are also going to be more likely to show a sensitization response.

And then I know I'm repeating myself a lot, but it's very important also [00:30:00] because the largest increases in habituation happen very early on. If you are not seeing signs of habituation in a moderate to strong response, that is also a predictor that sensitization may become more likely. Okay, so the last thing I wanna talk about is systematic desensitization.

And I included this as a separate thing. Because it's a little bit different. I mean, it is different than pure sensitization or desensitization. So the key word here is systematic. This is a very specific procedure that was developed for treating fears and phobias in humans. And the first thing that is done is the individuals are taught to relax.

So this is very, very important. This is the key part. Of systematic desensitization that the individual is taught to relax first, then that individual is [00:31:00] presented with the fear producing stimulus at a very low level while they remain relaxed. If they cannot remain relaxed during the presentation of that stimulus, it is too intense and something needs to be adjusted.

So if someone. Is trying to do systematic desensitization, and the animal is not relaxed throughout the entire process. It is not systematic desensitization. It might be desensitization alone without the systematic piece if the response is going down, but is very risky because again, if they're not relaxed, what are they?

They're more aroused, which means they're more likely to have. Continued sensitization. So if you're using the method of systematic desensitization, the animal needs to be relaxed throughout, and once you are confident they can be relaxed at one level of [00:32:00] the stimulus, then you would gradually increase it until they can be exposed to strong levels of that stimulus while remaining relaxed.

So I just wanna be really clear about that because I think a lot of people don't truly understand this element of being relaxed, and without that it is not systematic desensitization and it's much more risky to apply. So I also said that at the end I would talk a little bit about how, like what situations do we apply this in, right?

So let's say we have an animal We want to expose them to a stimulus. Well, there's two situations, right? So one situation is we wanna intentionally expose them to a stimulus to try to decrease their response. The other situation is that they get exposed to a stimulus without any intentionality on our part, and now we have to, you know, respond to that.

So if we look at. [00:33:00] Let's start with a situation where we're exposing the animal to a stimulus, right? So this might be something you're doing with a hunting dog. It could be a working dog, or it could simply be a companion animal. And I'm saying dogs, but this is gonna apply to pretty much all other species as well.

But maybe we wanna expose them to something that we know that they're gonna have to cope with, and we wanna get them used to it now. So veterinary care would be an example, right? So we know based on what we know about habituation, that when we're exposing them to these stimuli that we want them to habituate to that we want those stimuli to be not very arousing and not very strong.

So exposing a hunting dog to full on, you know, gunshots from the very start is not a very good way to habituate them. A sound, and again, there's no guarantee, right? You could start with stimulus stimuli that weren't very arousing and were weak, and you could [00:34:00] still get sensitization. But if we're playing the odds, the best way to do it is to expose them to stimuli that are less arousing.

That weaker and to monitor the animal's behavior very carefully and pivot very quickly if you're not seeing a change in that behavior. I'm gonna add to this, that we also have to think very carefully. Is habituation necessary in this case or can we avoid the stimulus or Better yet, and honestly, I mean, in many cases, I think this will be the answer.

Let's not do pure habitation or it wouldn't be habitation at all. Let's instead do conditioning work where we try and develop a positive association to something, right? So instead of just, I'm going to expose you to this sound and hope that you habituate to it. Instead, I'm going to expose you to this sound again at a low level, and then I'm gonna teach you that it predicts good things.

That is generally gonna be the [00:35:00] better response than trying to habituate them to something. But I still want you guys to understand the science behind it because this is going to help you make better decisions and develop better treatment plans. And then the other situation is that the animal being exposed to the stimulus, right, without any intentionality from the people behind it, it's just something that has occurred in the environment.

And so now we need to deal with it. And basically all of those things that I just said are still true. It's just that we're now reacting instead of being proactive. So those are the main points that I wanted to make about sensitization and habitation, and I would love to hear from you. About your response to this podcast and any questions you might have because this is not a topic that I've talked about before.

And if people have questions, I would love to try to answer them in a future podcast if there are enough questions to do so. So thank you very much.

Speaker 2: If [00:36:00] you enjoyed this content and would like to learn more, please visit www.sciencemattersllc.com. For more information, you can also find the link in the podcast description. The website has information on upcoming events, as well as my monthly research, webinars, and upcoming courses.

I hope to see you there. Thank you.