Stimulus filtering

from Wikipedia, the free encyclopedia

The filtering of stimuli is the central prerequisite for survival in their environment for all animals, but also to a certain extent for single-cell organisms and plants . Every living being constantly receives significantly more stimuli than the potential sensory cells or cell components and the cells downstream from them (cell components) could process.

Above all, animals have to be selective in a way that is appropriate for certain situations: They have to react to vital events in their environment and ignore less important ones, i.e. follow innate priorities . The phenomenon of stimulus filtering therefore also means that under certain circumstances a stimulus is followed by a certain reaction, but not under other circumstances.

Through stimulus filtering, sensory impressions are classified accordingly on the most varied levels of stimulus processing: already in the sensory organ, in the course of the transmission of excitation or in the central nervous system (in the form of selective perception ).

Types of stimulus filters

There are two types of stimulus filters:

  1. Rigid stimulus filters, so-called stimulus thresholds , which limit the maximum perceptible area. This restricts the perceptible area to the stimuli that are relevant for the survival situation of a living being.
  2. Variable stimulus filters that, depending on the situation, limit the perceptible range of stimuli to the range appropriate for this situation.

Examples

  • A rigid stimulus filter is e.g. B. the hearing threshold . This prevents irrelevant and annoying noises from leading to acoustic perceptions, such as B. the rustling of blood in the veins of the ear or the sounds of the heartbeat. On the other hand, areas that are irrelevant to survival are hidden (obviously it is not beneficial for humans to be able to hear the ultrasonic calls of the bats).
  • The human visual system also has a rigid stimulus filter so that ultraviolet radiation and infrared radiation are completely ignored.
  • Another fundamental mechanism of stimulus filtering are reflexes : They are only triggered by very specific stimuli.
  • Tilting figures are a well-known phenomenon of so-called multistable perception : They create a spontaneously changing perception (more precisely: interpretation) of a drawing, for example. With enough practice, this change can be brought about arbitrarily, but the perception variants can in no way be arbitrarily changed. Also, only one of the variants can be "seen" at a time, the alternative is suppressed by a filter mechanism.
  • Another particularly striking example are the receptive fields of the visual system. The result is a reduction and weighting of the excitations arising in the retina . In frogs, it has been shown that, thanks to stimulus filtering, special groups of light-sensitive cells preferentially direct the excitation they generate to the brain and can thus be used as prey detectors : They respond primarily to small, dark, moving objects in their field of vision.
  • So-called key stimuli enable innate reactions to vital stimuli: for example, newly hatched young birds open their bills when a parent settles on the nest (see also: Innate triggering mechanism ).

See also