Habituation is the earliest and the simplest type of learning. It has been observed in the youngest of infants and across the animal kingdom. Learning can be defined as an enduring change in the behaviour of a subject that is attributable to a specific experience. Habituation describes the decrease in intensity of a subject’s response to an experience, or stimulus, when repeated. Habituation is a learned regulation of behaviour and must not be confused with the diminished response of a subject due to sensory adaptation or motor fatigue.
An example of habituation can be found in the human startle response to loud noises. If you were reading a newspaper inside and the wind caused a wooden shutter to swing creating a peculiar noise, you would be startled and look up. The second time this happened you would not be alarmed but you would still notice the noise. After a few episodes, you wouldn’t even hear the sound that had previously distracted you.
Habituation, as a type of learning, is considered non-associative because the adapted behaviour of the subject is not influenced by either a reward or a punishment. When one associates the stimulus used to a positive or negative outcome, then it becomes a type of learning called Conditioning. This can be taken a step further by conditioning not only the response of the subject but the stimulus too: classical conditioning, as in the case of Pavlov‘s notorious dogs. Both habituation and classical conditioning are examples of learning that can be reversed.
The biological mechanisms of habituation have been observed in all species. They permit the nervous system to perform more efficiently by filtering out responses that are superfluous. The organism in question can therefore react more readily to the stimuli that could present a threat rather than those that have already proven to be innocuous.
The research and observation of habituation learning in multiple and extensively varied species was prevalent at the end of the nineteenth century and referred to using a plethora of different terms such as “acclimatization,” “accommodation,” “negative adaptation,” “fatigue,” “extinction,” “stimulatory inactivation.” By the mid-nineteenth century scientists assented that habituation was a recognisable phenomenon and an example of learning at its most basic level.