Threshold value (instinct theory)
Threshold value (also: entry threshold ) is a technical term of the instinct theory of classical comparative behavioral research (ethology) developed primarily by Konrad Lorenz and Nikolaas Tinbergen . Based on the stimulus threshold in sensory physiology , it denotes that minimum level of action-specific arousal that just enables instinctive movement when a key stimulus appears . “Stimuli that do not reach this value and therefore do not cause a recognizable reaction are called subliminal. Threshold values are not absolute values, but can be influenced by various indoor and outdoor conditions. "
The function of "thresholds" in instinct theory
According to George Barlow , the best-known model of how an animal becomes ready to act comes from Konrad Lorenz, who called it the psychohydraulic instinctual model. Lorenz assumed that in the central nervous system for every instinctive movement (meaning: "genetic coordination") an action-specific excitation is continuously produced and stored. This excitation builds up, as it were, and is then reduced in particular when the key stimulus associated with the respective instinctive movement is perceived and the instinctual movement then takes place. According to the model, the intensity and duration of the reaction to the key stimulus are dependent on the pent-up arousal, so “the willingness to perform an instinctive act is subject to fluctuations. [..] One encounters this phenomenon in a more or less pronounced way in all instinctual actions. ”One observes both“ Increase in willingness to act with the time lag to the last reaction sequence ”(the animal reacts to increasingly unspecific triggers with instinctual movements) and“ decline The readiness to act through abreaction. ”According to Konrad Lorenz, idling action (the willingness to act is so great that the instinctive movement due to a lowering of the threshold value runs without a recognizable key stimulus) and jumping movement (two conflicting readiness to act block each other) are a special case .
According to the instinct theory, the threshold for triggering an instinctive movement is determined by two independent influencing variables: On the one hand, by the cell groups in the interior that are constantly producing excitation, which Konrad Lorenz suspects, and on the other hand, by the quality of the external trigger. Lorenz explained the interaction of both factors the example of the fight behavior of cichlid -Männchen: "Lets be a Astatotilapia - that the strongest after repeated presenting male dummies is fought entirely ', a day or two to rest, one finds its readiness to act up to the previous Measure restored. If the test animal is kept from fighting stimuli for several days, its excitability not only increases to the previous, 'normal' level, but also far beyond it. The animal now responds to completely inadequate stimulus configuration, which does not characterize the biologically 'correct' environmental situation, with fighting movements. ”According to instinct theory, this response to inadequate stimuli is associated with appetite behavior , i.e. with an active search for a triggering stimulus.
criticism
In fact, identical stimuli can trigger different reactions in an animal at different times. For example, a bird that has not eaten food for a while will start looking for something tasty (appetite behavior) and eventually - if it has not found anything tasty for too long - be content with less popular food. Conversely, if this animal has eaten enough food, it will not eat anything again for a while, not even anything tasty. The interpretation of such observations with recourse to the hypothetical , constant excitation-producing cell groups, however, turned out to be the wrong path, since "no equivalent in the organism" was found. In addition, Konrad Lorenz had argued:
"There does not seem to be an instinctive movement in which the threshold value of triggering stimuli does not drop."
However, this assumption leads to " dysteleonomic " consequences; H. In 1992, for example, Hanna-Maria Zippelius objected to behaviors such as idling , the origin of which is inexplicable from an evolutionary perspective :
“An animal that lives without competition in its environment would have to show appetite behavior due to an impulse congestion, i. H. look for a rival to compete against in battle. […] An action-specific fatigue of the fighting instinct would also be regarded as dysteleonomic, as an animal in such a state no longer responds to the requirements of the environment, e.g. B. could answer in a meaningful way in the case of territorial or boy defense. "
It was also described as problematic that a theory only proves itself if the predictions made in it stand up to empirical testing. However, in order to show, for example, an increase in the threshold value in combat behavior in the experiment,
“It is usually necessary to carry out several attempts in a row with the same triggering object until the animal no longer responds to it. In a subsequent test it would then have to be shown that the behavior can be triggered again by an environmental situation with a higher stimulus value. With this procedure, it cannot be ruled out that the test animal may have experiences with the object presented several times in succession, which will influence its behavior in the subsequent test. For example, the lack of a reaction after multiple triggering of hereditary coordination could also be due to the learning process of getting used to it instead of action-specific fatigue , a process that occurs easily, especially with dummy experiments, as the animal's reaction to the initially triggering object through constant 'failures' adjusts. [...] Even if the test animal only answers objects with a higher stimulus value in the test, the experimenter cannot decide whether the animal reacts in this way depending on a low level of excitation of the drive energy or whether it reacts in this way on the basis of the experience that it was able to do in the successive attempts previously carried out, generalized about certain features of the offered objects and thus make a decision completely independently of its current energy level. "
Historical background
The emphasis on the spontaneity of animal behavior (as it happened in the construct of the threshold value , among other things ) and its explanation through physiological phenomena set up a counterpoint to behaviorism and its black box model and, in particular, to the view of the vitalists who It is true - as ethologists - spoke of instinct , but understood by this to be an extra-natural factor. Johan Bierens de Haan formulated his vitalistic position as follows in 1940:
"We look at instinct, but we don't explain it."
Today this statement may sound strange; However, even contemporary neuroscientists refrain from explaining many phenomena that are regarded as existing ( mind , reason , conscience , self-awareness ...), but about whose physiological or anatomical correlate little has been learned and their "explanation “One therefore leaves it to the philosophers or one's own old work.
Individual evidence
- ↑ Hanna-Maria Zippelius : The measured theory. A critical examination of the instinct theory of Konrad Lorenz and behavioral research practice. Braunschweig: Vieweg 1992, p. 10, ISBN 3-528-06458-7 .
- ^ Entry threshold in: Klaus Immelmann : Grzimeks Tierleben , supplementary volume behavior research. Kindler Verlag, Zurich 1974, p. 636.
- ↑ Konrad Lorenz : Comparative behavior research. Basics of ethology. Springer, Vienna and New York 1978, p. 143, ISBN 978-3-7091-3098-8 .
- ^ Uwe Jürgens and Detlev Ploog : From ethology to psychology. Kindler Verlag, Munich 1974, pp. 22-23, ISBN 3-463-18124-X .
- ↑ Konrad Lorenz: Comparative behavior research. Foundations of Ethology, p. 95.
- ↑ Wolfgang Schleidt (Ed.): The circle around Konrad Lorenz. Ideas, hypotheses, views. Paul Parey, Berlin and Hamburg 1988, p. 67, ISBN 3-489-63336-9 .
- ↑ Konrad Lorenz: Comparative behavior research. Foundations of Ethology, p. 104.
- ↑ Hanna-Maria Zippelius: The measured theory, p. 71.
- ↑ Hanna-Maria Zippelius: The measured theory, p. 74.
- ↑ Hanna-Maria Zippelius: The measured theory, pp. 68–69.
- ↑ Quoted from: Konrad Lorenz: Comparative Behavioral Research. Basics of Ethology, p. 2.