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.
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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
