Habituation (from Latin habituari : to have something in oneself or habitus : appearance, attitude; adjective habitual : become a habit), also known as habituation or habituation , describes the gradually decreasing willingness of an individual to respond “to repeatedly presented stimuli that have proven to be meaningless have ”and“ can be seen as one of the simplest forms of learning. ”The reaction to such a stimulus can ultimately be completely eliminated. If one keeps the stimulus away for a long enough time after this behavioral suppression, which is usually unconsciously “learned behavioral suppression” even in humans, the individual's strength of reaction increases again.
"The extinction differs from the habituation in that it occurs in connection with previously learned reactions, while in the habituation typically innate reactions occur that did not arise through a conditioning process ." The central nervous induced changes in the readiness to react due to habituation must also be distinguished on the adaptability caused by the periphery such as the adaptation of the hearing sensitivity to a continuous signal or the adaptation of the pupil to differences in brightness as well as on fatigue .
The opposite process - an increase in the strength of the reaction - is known as sensitization .
In 1944 , William Thorpe introduced the term "habituation" into behavioral terminology in a specialist article and defined it as "an activity of the central nervous system that causes innate responses to weak disturbance and warning stimuli to decrease if the stimulus persists over long periods of time," has no unfavorable effects ”( an activity of the central nervous system whereby innate responses to mild shock and warning stimuli wane as the stimuli continue for a long period without unfavorable results ).
Habituation in animals
Habituation has the effect that an animal learns not to react to certain stimuli , so that constantly existing stimulus patterns are hidden from perception and the individual is spared “useless” reactions.
A closely examined example is the gill- withdrawal reflex of the sea snail Aplysia californica , which the Nobel laureate Eric Kandel used as a model animal for his neurobiological studies: When the thin and vulnerable thread gills of this animal are touched by a foreign object, a protective reflex sets in and the gills become withdrawn. However, if these touches are carried out more frequently at short intervals, this reflex is reduced and ultimately stops completely. After a waiting period, the reflex reaction normalizes again and the snail responds to touching its gills by pulling them in.
Turkeys show a pronounced escape reaction from birds of prey , which can also be triggered with simple cardboard dummies moved over them. If they are kept close to geese living in the wild, they will initially flee from geese when they fly over them. However, they gradually get used to these birds that often appear above them and only flee from rarer and mostly singly circling birds.
Fruit growers know from experience that scarecrows set up to deter birds are only effective for a relatively short time because the birds get used to them quickly. Attempts to keep birds away from airfields by shouting warning messages over loudspeakers also resulted in similar habitat problems.
Habituation in humans
The Berlin pediatrician Albrecht Peiper published an early study in 1925 to prove habituation in humans , after he had found that newborns react to acoustic signals (sounds of a toy trumpet) with changed body movements just a few minutes after birth. He then tested whether unborn babies were reacting to such sounds by changing their kicking. His observations showed that the more often they were exposed to the sounds, the weaker the unborn child's reactions to a car horn. Other researchers were later able to show that newborns also react to repeated olfactory and visual stimuli with habituation if they remain without consequences, i.e. are not intensified .
Another example of habituation in humans is getting used to clothing, as is known to every nudist lover: Anyone who has not worn pants or a shirt for several weeks on vacation will be relieved by the constant pressure of the fabric against the skin when they return to textile culture and body hair may initially be considerably irritated, but after a short time have got used to this permanent stimulus again. Even new glasses can initially lead to irritations of this kind in the ears and nose, which are later lost due to habituation.
The fact that the phenomenon of habituation is not a mere “exhaustion” of the sensory cells involved in the perception of the stimulus can be easily understood from the following example: After a short time, people get used to the nocturnal, even hum of vehicles on one distant motorway until he finally no longer perceives this background noise as annoying. As soon as the noise stops, because you are staying in an absolutely quiet place, you notice that something is “wrong”.
Habituation as an influencing factor in behavioral tests
As useful as the mechanism of habituation is for animals and humans, it is problematic for behavioral researchers . In their experiments, they rely on repeatedly exposing their test animals to certain stimulus patterns in order to be able to formulate credible statements about the effect of a certain stimulus on their behavior . When planning the experiments, according to Walter Heiligenberg , care must therefore always be taken that long enough time intervals between the repetitions of the experiments can rule out a habituation of the test animals that would falsify the results of the tests with sufficient certainty.
Properties of habituation
A major problem in the detection of habituation is its delimitation from the fatigue of the organism and from sensory adaptation , which means that the perceived strength of a persistent stimulus decreases over time.
Suppose we are looking at a rat's response to a very bright light. At first, the rat shows a very strong startle reaction and briefly jumps into the air. As the stimulus is repeatedly presented, this response gradually decreases in strength. Is this decrease in response evidence of habituation? The decrease could also be due to fatigue in the rat, that is, if its muscles were fatigued, it would not be able to constantly produce a strong startle response. The decrease in response could also have been caused by sensory adaptation: in this case, the rat would no longer perceive the presentation of the initially disruptive stimulus as disruptive.
A number of properties that only occur in habituation help to distinguish it from other processes.
Habituation is stimulus-specific: the reaction only changes in relation to a certain stimulus. This distinguishes habituation from fatigue. If another stimulus is presented, the reaction to it is undiminished.
Suppose a rat has got used to the repeated presentation of a very bright light stimulus and no longer responds to it. Now she is exposed to a loud, piercing noise. If the animal shows a strong startle reaction, this would be evidence that the lack of reaction to the light stimulus is a result of habituation. However, if the rat showed no or only a weak reaction to the loud noise, this would be an indication of general fatigue.
Habituation is reaction specific. If a certain reaction to a stimulus no longer leads to a reaction, another reaction to the same stimulus can still occur. This allows habituation to be distinguished from sensory adaptation.
Assume that the smartphone has been assigned a new audio file as a ringtone without being noticed. Then the unexpected signal can cause a shock reaction, which does not occur after repeated hearing of the signal. Nevertheless, the upcoming conversation is accepted in every single case. A sensory adaptation would exist if, despite a repeatedly audible signal, a conversation never takes place due to a defect and the smartphone is therefore ignored despite the signal being given.
A distinction is made between two types of habituation with regard to the duration of the habituation effect:
This effect lasts for a comparatively long time. Take an abstract painting, for example. If we see this for the first time, we will devote a great deal of attention to it and look at the unusual representation for a while in astonishment. If we see the picture again later, we only look briefly and are no longer surprised because we already know it. So our reaction has become habituated. This habituation persists for a long time - even if we encounter the picture again after five weeks or more, our reaction will be greatly reduced compared to the first sight.
This form of habitation is relatively short in time. For example, when we go to a disco, the loud music may initially bother us. Over time, however, this reaction will become habitual and we will hardly be aware of the excessive volume. If we then leave the disco for a few hours and then enter it again, this habituation will no longer exist and the volume will disturb us again. The habituation effect is therefore of relatively short duration.
Short-term habituation can be observed e.g. B. also when habituations of test animals to aversive stimuli, z. B. Electric shocks .
An essential characteristic of short-term habituation in contrast to long-term habituation is the spontaneous recovery effect . This consists of a recovery of the reaction from habituation (i.e. an increased strength of the reaction) after a time-out . Time-out means that after habituation has been completed, this stimulus is no longer presented to the organism for a certain period of time (e.g. the rat is released into its home cage for 24 hours). If the stimulus is presented again after this break, then the previously habituated reaction occurs in a stronger form than at the end of the habituation phase. This effect is known as spontaneous recovery .
- Robert Hinde : Behavioral Habituation. Cambridge Univ. Press, New York 1970.
- HVS Peek and MJ Hertz (eds.): Habituation (2 volumes). Academic Press, New York 1973.
- Entry habituation in Klaus Immelmann : Grzimeks Tierleben , special volume behavior research. Kindler Verlag, Zurich 1974, p. 627.
- Walter Heiligenberg : The influence of specific stimulus patterns on the behavior of animals. In: Klaus Immelmann: Grzimeks Tierleben , special volume behavior research, p. 246.
- David McFarland: Biology of behavior. Evolution, physiology, psychobiology. 2. revised Edition. Spektrum Akademischer Verlag, Heidelberg 1999, p. 285, ISBN 978-3-8274-0925-6 .
- William Thorpe : Some Problems of Animal Learning. In: Proceedings of the Linnaean Society of London. Volume 156, No. 2, 1944, pp. 70-83, doi: 10.1111 / j.1095-8312.1944.tb00374.x .
- Harold Pinsker, Irving Kupfermann, Vincent Castellucci and Eric Kandel : Habituation and Dishabituation of the GM-Withdrawal Reflex in Aplysia. In: Science . Volume 167, No. 3926, 1970, pp. 1740-1742, doi: 10.1126 / science.167.3926.1740 .
- Thomas J. Carew, Vincent F. Castellucci and Eric R. Kandel: An Analysis of Dishabituation and Sensitization of The Gill-Withdrawal Reflex in Aplysia. In: International Journal of Neuroscience. Volume 2, No. 2, 1971, pp. 79-98, doi: 10.3109 / 00207457109146995 .
- Thomas J. Carew, Harold M. Pinsker, and Eric R. Kandel: Long-Term Habituation of a Defensive Withdrawal Reflex in Aplysia. In: Science. Volume 175, No. 4020, 1972, pp. 451-454, doi: 10.1126 / science.175.4020.451 .
- Irenäus Eibl-Eibesfeldt : Outline of Comparative Behavioral Research. 7th edition. Piper, Munich and Zurich 1987, p. 419, ISBN 3-492-03074-2 .
- Irenäus Eibl-Eibesfeldt: Outline of Comparative Behavioral Research, pp. 166–167.
- Albrecht Peiper : Sensory sensations of the child before its birth. In: Monthly for Pediatrics. Volume 29, 1925, pp. 237-241.
- Walter Heiligenberg: The influence of specific stimulus patterns on the behavior of animals, p. 249.