Sensitization and habituation

Sensitization and habituation are two essential terms when it comes to animal research. They describe the way animals' reactions change to a specific stimuli over time. After every time a stimulus is met, learning occurs. The animal is changed through the experience, and these changes lead to a more profound, noticeable change if the stimulus is repeated. 

Sensitization happens when after repeated occurrences, usually with a lot of time in between them, an animal starts to react more strongly to a stimulus. Their reaction may be more pronounced, and the physiological measurements (blood pressure for one) can be more extreme than before. Examples of sensitization:

• Repeating unpleasant handling. Animal learns that the experience is painful, and can start reacting even stronger every time. (for humans this can be the case with dentist's appointments).
• Loud, sudden sounds like fireworks on New Year's Eve. A dog may not react to the first bangs, but as they keep repeating on uneven intervals, the dog starts reacting more and more strongly during the evening and night. 
• Traumatic event, which leads to fear of smells, sights or other items that coincided with the place of the original event. 

Sensitization usually does not last for very long. The stronger the stimulus, the longer the sensitization lasts. Makes sense, doesn't it - after a quiet "pop!" we're jumpy for a while, but after the bang of explosion the jitters are considerably worse!

Sensitization is not very specific to a stimulus. An unpleasant experience at the veterinarian can cause sensitization towards the vet, but also towards people with similar clothes, the physical location or the smells that were present.  

(c) https://www.dreamstime.com/

Habituation is the opposite of sensitization. According to Lumen Learning, "Habituation occurs when we learn not to respond to a stimulus that is presented repeatedly without change, punishment, or reward". Something happens, but nothing follows from it - therefore it's not needed to react to this stimulus. Broom uses an example where a flock of sheep is moved from a quiet pasture to a field next to a road. At first, they will react to every passing car. As the cars keep on driving by, they get used to it and react less and less. You could say they got bored of the cars, which is in a sense correct. The more scientific terms is that they've habituated.

Other examples of habituation are

• Habituation to humans and human touch
• Habituation to light-dark rhythm.

Habituation is very stimulus-specific. An animal might habituate to a specific type of noise, but if it changes in volume, pitch or sound, the animal will react to it again. In our example the sheep might ignore a car, but react strongly to a Harley-Davidson.

Habituation rely heavily on repetition. Factors influencing the result are regularity (how often does the event repeat), pattern (does it repeat in an predictable interval) and time between repetitions. For example, animals habituate quickly to stimulus repeating often in a short time. However, the recovery (when the habituation wears off) is also quick.

 

More on habituation and sensitization

Biological Basis of Learning | Boundless Psychology (lumenlearning.com)

Microsoft PowerPoint - Learning.ppt (ucsd.edu)

 

Types of animal welfare studies

 When talking about animal experiments, it's easy to start thinking along the lines of mice, needles and electric shocks. But there are naturally a lot of other kinds of experiments as well. Consider a simple case where an animal is offered two kinds of food to see which one they choose first. That is also research on animals!

The study of animal welfare is a very complex field. Just to start with: what IS welfare and how to measure it when the animal itself cannot talk or describe it's emotional states? Obviously a complicated set of research methodologies is needed to achieve robust results. The measurements taken to achieve the results can be roughly divided into two: physiological and behavioral.

Physiological	Behavioral
Temperature Heart rate Blood glucose Fat percentage Weight Bacterial count	Time spent sleeping Frequency of a specific behavior Posture changes Social contacts Time taken to approach objects Distance traveled to forage

As you can see, welfare can actually be quite specific!

Next, let's have a look at some types of studies which are conducted to find out more about animal welfare. All of the measurements listed above are just data, but it's of course important to know how to gather the data to make sure - you guessed it - that the data is correct. So what kind of experiments are used?

Preference studies

Preference and motivation studies are both examples of empirical study, where the researcher gathers data on the target of their study. In preference studies the animals choose what they prefer and what factors influence the preference.

An example of preference study is to offer chickens feed with and without NSAIDs (painkillers). Chickens with healthy feet eat more of the feed without medication, while chickens with leg sores and ulcerations prefer the feed with the medication (self-medication). Factors affecting the preferences can be available time, diet, health and pregnancy.  

(c) Louse Buckley, UFAW

Motivation studies

Motivation study measures the motivation or willingness of an animal to reach a specific goal. The aim is to find out the value of things  and what impacts the motivation. For example, an animal might be very motivated to get a treat when alone, but less motivated when they're in a group and know they might need to share their treat. Measurements can be speed and distance traveled to the goal,  latency before the animal tries to reach the goal and energy spent to reach the goal.

In classic examples animal can be trained to press a lever to get a specific treat. Then the treat is disabled, and the amount of times the animal presses the lever trying to get the treat is the "price" they're willing to pay for it. Things like temperature, eating, health and group size can all affect the value of the reward. 

Metastudy

Metastudy is different from the other types, because this is the study of studies. In metastudies the researchers gather a vast amount of previous researches, carefully select the most relevant ones and summarize their findings. The process of selection and omission must naturally be well documented and argumented. The aim is to see wider trends and generalizations. Commonly seen phrases like "many studies prove" or "there is little scientific base on the claim that" arise from metastudies. Metastudy goes further than just being a literature review. It uses for example statistical methods to compare the results of the studies once comparativeness is established.   

More information:

Animal welfare science - Wikipedia

Consumer demand tests (animals) - Wikipedia