Key stimulus

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Key stimulus (occasionally also: trigger , signal stimulus or perception signal ) is a technical term of the instinct theory of classical comparative behavioral research (ethology) developed primarily by Konrad Lorenz and Nikolaas Tinbergen . It describes a certain stimulus that acts on an animal from the outside and results in a certain innate , " phylogenetically programmed, hereditary-coordinated movement" ( instinctive movement ), with the help of which the environmental situation determined by the key stimulus is mastered with "innate ability" without prior learning. The rank of a key stimulus can also "be assigned to a combination of features, whereby the rule for the combination of features is that they are only effective if they are fully represented and the sub-elements are arranged in a specific manner."

Historical

“Viewed in a historical context, the beginnings of ethology fall in the heyday of reflexology and behaviorism , in a dualism of stimulus and reaction that is based on the concepts of classical mechanics [...]. The concepts of 'key stimulus ' and ' gestalt ' developed first as additional hypotheses of the stimulus-response scheme and then - by emphasizing the interplay of external stimuli and internal drives ( instincts ) - as an alternative to behaviorism and reflex chain theory .

The term key stimulus was introduced in 1935 by Konrad Lorenz in his early work Der Kumpan in der Vogel Umwelt des Vogels as a technical term in behavioral biology ; A year earlier, however, Lorenz had already described in an anecdote during a lecture in Oxford how jackdaws behaved and compared it to a gate that is opened by a key. 1978 pointed Lorenz also that the American Ornithologist Francis Hobart Herrick (from 1858 to 1940) "already more than half a century" in the context of instinctive movements, the metaphor "lock and key" ( lock and key was used). In 1935, Lorenz took up this metaphor by comparing the external stimulus - the “triggering scheme” - with the beard of a certain key which, when inserted into a suitable lock, induces a certain instinctive reaction. In this early work, the “triggering scheme” was also referred to with the synonym key stimulus, but in 1935 the sequence of key stimuli and associated instinctive movement was still close to the stimulus-reaction scheme prevailing at the time, since Lorenz only described the properties of the “lock” in relation to the construction of the "key". It was not until the following year that Nikolaas Tinbergen and Konrad Lorenz “ born” the later so-called innate triggering mechanism (AAM), a “switching point” that gives the specific “input” a specific “switch ” “in night-long discussions” during a symposium on the subject of instincts . Output 'follow; instead of AAM, however, the designation triggering scheme was chosen in 1936.

Key stimulus and innate trigger mechanism (AAM)

In his textbook Comparative Behavioral Research. Basics of ethology Konrad Lorenz defined the key stimulus in 1978 as the “stimulus configuration to which an AAM responds”, but only if and only if there is also a sufficiently large amount of “a permanently endogenously produced” action-specific stimulus. Conversely, the 'switching point' of an instinctual act - postulated as a subsystem of the central nervous system - picks out like a filter “a small selection from the abundance of stimuli”, a selection to which the AAM responds selectively “and thus sets the action in motion” Core elements of instinct theory - readiness to act (“motivation”), key stimuli, innate trigger mechanisms and instinctual movements - were countered by Lorenz and other ethologists in particular to the behaviorists' claim that only learning processes can be measured experimentally. “Lorenz found this 'scientific landscape' at the beginning of his research. He countered it with his thesis that animals have innate abilities which - that is the decisive factor - are definitely accessible to causal analysis. He also emphasizes that learning processes can only be correctly assessed on the basis of knowledge of innate abilities. "

In 1992, Hanna-Maria Zippelius pointed out in a detailed analysis of the instinct theory that Konrad Lorenz had "fundamentally modified his original key-lock concept" apparently unnoticed by the public, "without, however, on the meaning that he had changed over time" the term key stimulus. Zippelius reported that according to the key-lock principle, animals are only asked whether the key stimulus is present or not, without taking into account possible different forms of the stimulus: "This means that the decision is made solely through the innate trigger mechanism, whether or not the answer will be carried out if there is a sufficient level of specific motivation. "The lock-and-key principle only allows yes or no decisions depending on the presence or absence of the key stimulus:" The lock is used when comparing To stay Lorenz, either open-minded or not. Such a recognition mechanism is not very flexible and only decides whether a response is given or not. ”In contrast to this idea, Lorenz wrote in later years in the plural that key stimuli“ can be summed up ”and“ basically function independently of one another. ”Zippelius names these features as "Key components" that trigger a response alone or in any combination with other components, provided that the stimulus values ​​are above the respective trigger threshold. According to Zippelius, the qualitative novelty of the key component concept compared to the key-lock concept consists “in addition to the independence of the key components from each other also in the fact that an animal not only asks the environment for the presence or absence of a key stimulus, but also that it is aware of the different characteristics of the Key components are considered in order to evaluate them depending on their design. ”The assumptions of this extended key stimulus concept result in a recognition mechanism that is much more flexible than an AAM that works according to the key-lock principle.

Two further developments can be derived from the facts presented. On the one hand, it can happen that the willingness to act for an instinctive movement is sufficiently great due to the associated action-specific arousal produced, but no key stimulus appears that can induce the instinctual movement. In this case, in the context of instinct theory, reference is made to the possibility of lowering the threshold value and an idle action. On the other hand, it can happen that two different, but equally strong triggers appear at the same time; in this case, reference is made to the so-called skipping movement .

A key stimulus can also be learned through imprinting in a certain, sensitive phase of life.

features

A key stimulus is regularly described in the behavioral literature as:

  • simple, it consists of only a few features
  • conspicuous, it can hardly be overlooked
  • clearly, it is easy to distinguish from other stimuli.

It can be triggered in many different ways, in particular:

Key stimuli are, as it were, abstract , symbolic . Not “the bird of prey in the sky” - as we humans perceive it “ as a whole ” - is the trigger for a newly hatched curlew or turkey to take refuge in the nearest cover, but a circling black spot in the bright sky. The observer, however, may only notice this by chance because the chick has made a mistake, because it shows the same behavior "when a black fly runs across the whitewashed ceiling."

According to Konrad Lorenz, the selection of stimulus configurations to which an AAM responds is “always made in such a way that an overly frequent 'erroneous' response, which is dangerous for the species, is sufficiently improbable. The classic example of this is the stinging reaction of the female tick ( Ixodes ricinus ), which responds to a combination of two stimuli belonging to different sensory areas: the object must have a temperature of around 37 degrees Celsius and smell of butyric acid . In addition, part of the overall course of behavior is that the tick sits on plants and, when they are struck, lets go of them and falls on the object causing the movement. If it smells like butyric acid and is warm, then it stings. Imagine how unlikely it is that the stimuli provided for in the phylogenetic program would 'erroneously' cause the animal to sting something other than the appropriate object, a mammal. "

Another example of key stimuli that Konrad Lorenz cites is human behavior: “His brood-care actions respond to a number of configuration features that can be exaggerated. They include a high round forehead, a predominance of the brain skull over the facial skull , a large eye, a round cheek area , short thick extremities and a rounded body shape. Movement characteristics are accompanied by a certain awkwardness, an ataxia especially of the locomotion , everyone knows how touching a child who is just able to walk becomes when it cannot stop in the direction of the desired goal. […] The industry has found out that human susceptibility to supernormal dummies can be financially exploited. Primarily the doll industry did this ”. These observations are based on the designation child schema .

controversy

The “innate recognition” of a biologically relevant environmental situation has been proven many times by behavioral researchers and neurophysiologists and is considered to be certain. For example, the biochemist Adolf Butenandt reported as early as 1955 on the effect of sexual attractants on insects , and a few years later he identified a chemical substance in the silk moth (Bombyx mori) , which he named as bombykol , which is sent by females ready to mate and sexually mature males out of several hundred Meters away. With the help of behavioral experiments and electrophysiological methods it has been proven that the olfactory receptors on the antennae of the silk spider males respond specifically to the insect pheromone bombykol and that the males can localize a female of their species without prior learning. In the nightingale grasshopper , on the other hand, specific features of stridulation (the “song”) of sexually mature males were identified (a certain ratio of syllable duration to the duration of the pauses between the syllables) that attract native females. The mentioned stimuli that bring about a rapprochement between the sexual partners can be figuratively named as “key stimuli”, but this designation no longer refers to the ethological model of instinct. Even the neuroethologist Jörg-Peter Ewert , who described the triggering mechanisms of common toad prey in precise mathematical terms (only a moving object of a certain size and sufficiently elongated triggers prey-catching behavior) and the metaphor of the triggering mechanism - applied in terms of the rules - for his research area in 1994 as contemporary felt, but warned "against the possibility of misinterpretation of the term 'key stimulus'" and justified this as follows: "The visual key of prey of the common toad is not represented by an identifier or a specific set of characteristics, [...] the 'key' is with the specificity of the algorithm that differentiates between prey and non-prey by analyzing the geometry of a moving object in relation to its movement (direction). "

In the ethological specialist literature, a key stimulus was also regularly defined by its ability to release the action-specific energy prevented by an AAM (with sufficient motivation) from “flowing away” and thus triggering an instinctive movement. At the same time, however, the AAM (i.e. the release of a behavior appropriate to the situation) was shown as evidence of the existence of a key stimulus - which corresponds to a circular argument. Difficulties in definition, uncertainties in precisely describing the characteristics that make up a key stimulus and the lack of any physiological correspondence to the “energies” provided for specific actions, etc. a. In 1990 Wolfgang Wickler and 1992 Hanna-Maria Zippelius prompted them to aggressively call for the instinctual model of classic comparative behavioral research to be dispensed with . Even Klaus Immelmann did not even include the word key stimulus in the keyword register in 1987 in the Funkkolleg on the subject of psychobiology for which he was responsible and which was particularly well received by teachers . Finally, it also contributed to the move away from the fact that some of the best-known classic examples of key stimuli that have been used in many school and textbooks did not withstand scrutiny.

  • For example, at the end of the 1980s in Bonn, a test was carried out to determine which innate traits a newly hatched herring gull chick uses to identify who to beg for food. According to a study published in 1950 by Nikolaas Tinbergen and Albert C. Perdeck, they identified “a spot (preferably a red one) near the tip of the lower jaw” of an adult herring gull as a key stimulus. Tinbergen and Perdeck had taken "dry" or "almost dry" chicks in the field from nests and tested them in a test tent. In order to be sure that the chicks could be tested without experience - i.e. without ever having seen adult gulls - gull eggs were removed from a colony on Langeoog for the Bonn control experiments and hatched in the laboratory. A total of 112 chicks were tested, with the result that the chicks begged a green, yellow, blue and white speckled head dummy and various other colors in a two-fold choice experiment with the same frequency and a blue and white painted ball even more often as "parent animal" than nature - faithfully designed white and yellow head dummy with red dot on the lower beak.
  • In his book Instinct Theory in 1952, Tinbergen described his own field experiments with oyster fishermen and herring gulls, for which he had placed artificial eggs next to their clutch, one normal-sized and one significantly larger. According to his observations, the breeding gulls preferred to roll the oversized eggs into their nests. Irenäus Eibl-Eibesfeldt took this finding into his textbook Grundriss der Comparative Behavioral Research in 1967 and interpreted it from an evolutionary point of view: “The fact that triggering stimuli can be exaggerated also shows that the evolution of the existing trigger is not necessarily complete. One of the reasons for this may be counteracting selection pressure. A signal should be as conspicuous as possible and at the same time unambiguous, i.e. H. be unmistakable, otherwise there would be errors. The signal receiver thus exerts a selection pressure in the direction of conspicuousness while at the same time making the signal transmitter unmistakable. Those who are conspicuous, however, are also easily perceived by their predators, who accordingly exert selection pressure in the opposite direction. The result is often a compromise. ” Gerard Baerends was not able to confirm the findings satisfactorily in 1982, and in 1986 control experiments with herring gulls in Bonn also found no confirmation of the preference for larger than normal dummies.
  • A house mouse mother who raises nestlings returns her young to their nest when they are out of the nest. In the 1950s, ethologists had described the chirping noises of nestlings as the triggering stimuli for this entry behavior , so that the assumed combination of "cry for help" and "help" even found its way into the renowned zoological handbook . In 1989, however, it was experimentally proven in Frankfurt am Main that dead boys and even carcass parts were also registered; the assignment of the vocal utterances as a key stimulus for the feeding behavior turned out to be an anthropomorphic misunderstanding and insofar as erroneous, instead the smell was considered as a trigger. The feeding behavior is also - apart from all key stimuli to be considered - hormonally controlled: In 2015 it was shown that the willingness to feed in female mice mainly depends on their oxytocin level . After injections of this hormone, the females also brought in unfamiliar cubs, even if they had not yet had motherhood experience but were virgins. Stressed females, on the other hand, refrained from rescuing boys or even doggedly squeaking boys.
  • “There is probably no curriculum or textbook that does not contain this 'classic' example of stickleback behavior . […] One should be very careful with this example. ”This warning in a textbook for didactics of biology refers to an early publication by Nikolaas Tinbergen in the Zeitschrift für Tierpsychologie , whose findings Tinbergen in his 1952 instinct theory published as valid mentioned. Accordingly, the red throat and the red belly of male sticklebacks are a key stimulus for triggering combat behavior against intraspecific rivals. In 1985, a control study failed to confirm Tinbergen's description. Other studies from the 1990s could not confirm the red stomach as the primary trigger. Conclusion: "The red belly is not absolutely necessary to trigger combat behavior."

In her criticism of the instinct theory and the ethological key stimulus concept, Hanna Maria Zippelius summarized discrepancies from a behavior- ecological point of view in 1992 . The assumption that the design of a signal is determined by the motivations involved in each case implies that "an animal transmits very precise information about its condition to the recipient of this signal." Threatening gesture read whether the sender is more aggressive or more aggressive, and he could possibly evaluate this information for his benefit. “The question arises as to whether it is advantageous for the sender to pass on such, possibly very precise information about their own condition to the recipient. [...] A fighter who intends to give up the fight soon should not announce this to his competitor beforehand. "

See also

literature

  • Irenäus Eibl-Eibesfeldt : Technique of comparative behavior research . In: Handbook of Zoology. A natural history of the tribes of the animal kingdom . 8th volume, 31st delivery, Walter de Gruyter, Berlin 1962.

Individual evidence

  1. ↑ Konrad Lorenz : Comparative behavior research. Basics of ethology. Springer, Vienna and New York 1978, p. 122, ISBN 978-3-7091-3098-8 .
  2. ↑ Hanna-Maria Zippelius : The measured theory. A critical examination of the instinct theory of Konrad Lorenz and behavioral research practice. Vieweg, Braunschweig 1992, p. 37, ISBN 3-528-06458-7 .
  3. ↑ Wolfgang Schleidt : Patterns in behavior and the environment. What does 'innate' mean in behavior and perception of the environment? In: Gerd-Heinrich Neumann and Karl-Heinz Scharf (eds.): Behavioral biology in research and teaching. Ethology - Sociobiology - Behavioral Ecology. Aulis Verlag Deubner, Cologne 1994, p. 30, ISBN 3-7614-1676-8 .
  4. ↑ Konrad Lorenz: The friend in the environment of the bird. In: Journal of Ornithology. Volume 83, No. 2-3, 1935, pp. 137-215 and pp. 289-413, doi: 10.1007 / BF01905355 .
  5. ^ Konrad Lorenz: A contribution to the comparative sociology of colonial-nesting birds. In: The Proceedings of the Eight International Ornithological Congress Oxford 1934. University of Oxford Press, Oxford 1938, p. 211, full text (PDF) .
  6. ↑ a b c Konrad Lorenz: Comparative behavior research. Basics of Ethology, p. 124.
  7. ^ Francis Hobart Herrick : The Blending and Overlap of Instincts. In: Science. Volume 25, No. 646, 1907, pp. 781–782, doi: 10.1126 / science.25.646.775 , full text .
  8. ↑ Konrad Lorenz: The friend in the environment of the bird. Reprinted in: The Same: About Animal and Human Behavior. From the development of the theory of behavior. Collected papers, Volume 1, p. 117, Piper, Munich 1965, ISBN 3-492-01385-6 , full text (PDF) .
  9. ↑ Konrad Lorenz: Comparative behavior research. Basics of Ethology, p. 6.
  10. ↑ Konrad Lorenz: Comparative behavior research. Foundations of Ethology, p. 95.
  11. ^ Konrad Lorenz: Der Kumpan in der Umwelt des Vogels, reprint, p. 268.
  12. ↑ Hanna-Maria Zippelius: The measured theory, p. 27.
  13. ↑ Hanna-Maria Zippelius: The measured theory, pp. 37–38.
  14. ↑ Konrad Lorenz: Comparative behavior research. Fundamentals of Ethology, pp. 127–128.
  15. ↑ Konrad Lorenz: Comparative behavior research. Fundamentals of Ethology, p. 126.
  16. ↑ Konrad Lorenz: Comparative behavior research. Basics of Ethology, pp. 130–131.
  17. ↑ Adolf Butenandt : About active ingredients of the insect kingdom. II. Knowledge of sex attractants. In: Naturwissenschaftliche Rundschau. Volume 12, 1955, pp. 457-464.
  18. ↑ Dagmar von Helversen : Singing of the male and sound scheme of the female in the field locust Chorthippus biguttulus (Orthoptera, Acrididae). In: Journal of comparative physiology. Volume 81, No. 4, 1972, pp. 381-422, doi: 10.1007 / BF00697757 .
  19. ↑ Dagmar von Helversen and Otto von Helversen : Correspondence between song and triggering scheme in field locusts. In: Nova Acta Leopoldina Suppl. NF. Vol. 54, No. 245, 1981, pp. 449-462.
  20. ↑ Jörg-Peter Ewert : Neuroethology of releasing mechanisms: Prey-catching in toads. In: Behavioral and Brain Sciences. Volume 10, No. 3, 1987, pp. 337-368, doi: 10.1017 / S0140525X00023128 .
  21. ↑ Jörg-Peter Ewert: Is the concept of the release mechanism still up to date? In: Gerd-Heinrich Neumann and Karl-Heinz Scharf (eds.): Behavioral biology in research and teaching. Ethology - Sociobiology - Behavioral Ecology. Aulis Verlag Deubner, Cologne 1994, p. 223, ISBN 3-7614-1676-8 .
  22. ↑ Jörg-Peter Ewert: Is the concept of the release mechanism still up to date? , P. 207.
  23. ↑ Hanna-Maria Zippelius: The measured theory, p. 13.
  24. ↑ Wolfgang Wickler : From ethology to sociobiology. In: Jost Herbig, Rainer Hohlfeld (ed.): The second creation. Spirit and Demon in 20th Century Biology. Hanser, Munich 1990, p. 176, ISBN 3-446-15293-8 .
  25. ↑ Klaus Immelmann et al. (Ed.): Funkkolleg Psychobiologie. Behavior in humans and animals. Cover letters 1–10. Beltz, Weinheim 1986 and 1987.
  26. ↑ Nikolaas Tinbergen and Albert C. Perdeck: On the Stimulus Situation Releasing the Begging Response in the Newly Hatched Herring Gull Chick (Larus Argentatus Argentatus Pont.). In: Behavior. Volume 3, 1950, pp. 1-39, doi: 10.1163 / 156853951X00197 .
  27. ↑ Nikolaas Tinbergen: Instinct theory. Comparative research into innate behavior. Parey, Berlin and Hamburg 1952, p. 72.
  28. ↑ Ursula Eypasch: The interaction of innate evaluation and experience in solving a recognition problem, investigated on young herring gulls (Larus argentatus Pontopp.). Dissertation. University of Bonn, Bonn 1989, p. 42.
  29. ^ Irenäus Eibl-Eibesfeldt : Outline of Comparative Behavioral Research. 7th edition. Piper, Munich and Zurich 1987, pp. 174-176, ISBN 3-492-03074-2 .
  30. ↑ Gerard Baerends : The Effectiveness of Different Egg Features for the Egg-Retrieval Response. In: Behavior. Volume 82, No. 4, 1982, pp. 33-224, doi: 10.1163 / 156853982X00607 .
  31. ↑ Hanna-Maria Zippelius: Die measured theory, p. 165.
  32. ^ Irenäus Eibl-Eibesfeldt : The behavior of the rodents. In: Johann-Gerhard Helmcke et al. (Ed.): Handbuch der Zoologie. Volume 8, Delivery 10, No. 13, pp. 1-88. de Gruyter, Berlin 1958.
  33. ^ Karl-Heinz Wellmann : On the effect of disruptive selection on the behavior of house mice: registering nestlings, further elements of brood care behavior and exploration . Dissertation, University of Frankfurt. Wissenschafts-Verlag Wigbert Maraun, Frankfurt am Main 1989, ISBN 3-927548-18-9 .
  34. ↑ Bianca J. Marlin et al .: Oxytocin enables maternal behavior by balancing cortical inhibition. In: Nature . Volume 520, 2015, pp. 499-504, doi: 10.1038 / nature14402 .
    'Love hormone' turns mothers into moms. On: sciencemag.org from April 15, 2015.
  35. ↑ Gerd-Heinrich Neumann: Treatment of behavioral biology in both secondary levels. In: Derselbe and Karl-Heinz Scharf (eds.): Behavioral biology in research and teaching, p. 247.
  36. ↑ Jan Joost ter Pelkwijk and Nikolaas Tinbergen: A stimulus-biological analysis of some behaviors of Gasterosteus aculeatus L. In: Zeitschrift für Tierpsychologie . Volume 1, No. 3, 1937, pp. 193-200, doi: 10.1111 / j.1439-0310.1937.tb01422.x .
  37. ^ William J. Rowland and Piet Sevenster: Sign Stimuli in the Threespine Stickleback (Gasterosteus aculeatus): A Re-Examination and Extension of Some Classic Experiments. In: Behavior. Volume 93, No. 1/4, 1985, pp. 241-257, doi: 10.1163 / 156853986X00919 .
  38. ↑ Jürg Lamprecht: Dummy experiments with sticklebacks: Are the results of Niko Tinbergen artifacts? In: Biology in Our Time. Volume 23, No. 5, 1993, pp. 67-69, doi: 10.1002 / biuz.19930230512 .
  39. ↑ Gerd-Heinrich Neumann: Treatment of behavioral biology in both secondary levels, p. 258.
  40. ↑ Hanna-Maria Zippelius: The measured theory, p. 272.