Stimulus threshold

In electrophysiology and sensory physiology, the stimulus threshold is understood to be that threshold of intensity that a stimulus must at least reach in order to trigger an excitation , a sensation or a reaction .

Supra- threshold stimuli are changes of different forms of energy in the environment of an organism or a cell , which, depending on the type, intensity and duration or repetition of the stimulus, exceed the threshold intensity and cause specific changes as adequate stimuli . According to the energetic type, a distinction is made between chemical, osmotic, thermal, mechanical, acoustic, electrical, electromagnetic or optical stimuli and for these different stimulus thresholds, which are further differentiated depending on the sensory modality and quality . For example, one speaks of the odor threshold for a certain fragrance, the hearing threshold for certain frequencies and the visual threshold in the scotopic area after a certain adaptation time .

In physiology is both the smallest stimulus intensity that even as stimulus acts as a threshold called. But this can refer to the triggering of an excitation of a single cell, or to the elicitation of a sensation as a sensory impression of a perceiving organism. Depending on the reference, the stimulus threshold can mean a different intensity threshold .

• At the level of a cell, stimulus threshold electrophysiologically means the threshold for an excitation formation: in a sensory cell the threshold from which a change in the resting membrane potential is generated as generator potential and in a (1st) afferent nerve cell reaches the threshold from which an excitation is triggered and a Action potential is formed, the threshold potential . In a similar way, the term stimulus threshold is used for cardiac muscle cells , for example stimulus threshold measurement in connection with a pacemaker .

• At the level of a multicellular organism, stimulus threshold means, in terms of physiology, the threshold for a sensory perception: the smallest stimulus intensity that just causes a sensation with a certain stimulus constellation. This stimulus threshold, abbreviated to RL (for stimulus limen ; Latin limen 'threshold' ), was also referred to as the absolute threshold . Some authors only address the smallest possible value of the stimulus threshold under optimal conditions of the stimulus constellation and adaptation as the absolute threshold .

With regard to the stimulus threshold, a conceptual clear distinction is not always made between a threshold from which a stimulus as such is even noticeable (such as “something”) and that from which a sensory impression arises (such as “red”). This must be delimited from a threshold from which a sensation is formed (such as “red dots”) or that from which a perception is assigned (such as “red blood cells”). The latter two are also referred to as the detection threshold . Determinations of such thresholds are usually dependent on subjective information.

Above the absolute threshold of perception ( absolute threshold ) more sensory thresholds are differentiated. This includes the (intensity) difference threshold according to the ability to compare similar stimuli with regard to their intensity (as “stronger” / “weaker”). Other thresholds that are important for the discrimination of stimuli are those for spatial (as "next") and temporal (as "after") resolving power.

The stimuli (around 10 ⁹ bit / s) received by the sensory cells and by the first afferent neurons are contrasted and filtered in a human nervous system so that only a few (10–100 bit / s) are consciously perceived. Ingested, but unconsciously effective stimuli are called subliminal .

The best pest method is used to determine a subject's threshold of perception for a stimulus. Particular stimulus thresholds are, for example, the wake-up threshold , the discomfort threshold and the pain threshold .

See also

• Threshold value (instinct theory)

literature

• Robert F. Schmidt , Gerhard Thews , Florian Lang (Hrsg.): Physiologie des Menschen. 28th edition. Springer, Berlin et al. 2013, ISBN 3-662-09346-4 .

Individual evidence

1. ↑ Cf. entry stimulus in the Lexicon of Neuroscience on Spektrum.de; accessed on September 27, 2019.
2. ↑ ^{a b} H. Handwerker: Allgemeine Sinnesphysiologie. In: R. Schmidt, G. Thews, F. Lang (Hrsg.): Physiologie des Menschen. 28th edition, 2013, pp. 207f .
3. ↑ ^{a b} H. Antoni: excitation physiology of the heart. In: R. Schmidt, G. Thews, F. Lang (Hrsg.): Physiologie des Menschen. 28th edition, 2013, p. 476.
4. ↑ G. Fröhlig et al .: Pacemaker and Defibrillator Therapy. Thieme 2013, doi: 10.1055 / b-0034-88294 , chapter Algorithms for output control .
5. ↑ ^{a b} Stefan Silbernagl , Agamemnon Despopoulos : Pocket Atlas Physiology . 8th edition. Thieme, Stuttgart 2012, ISBN 978-3-13-567708-8 , p. 330 .