Stimulus filtering occurs when an animal's

nervous system In biology, the nervous system is the highly complex part of an animal that coordinates its actions and sensory information by transmitting signals to and from different parts of its body. The nervous system detects environmental changes th ...

fails to respond to

stimuli A stimulus is something that causes a physiological response. It may refer to: * Stimulation ** Stimulus (physiology), something external that influences an activity ** Stimulus (psychology), a concept in behaviorism and perception * Stimulus (eco ...

that would otherwise cause a reaction to occur. The nervous system has developed the capability to perceive and distinguish between minute differences in stimuli, which allows the animal to only react to significant impetus. This enables the animal to conserve energy as it is not responding to unimportant signals.

Adaptive value

The proximate causes of stimulus filtering can be many things in and around an animal's environment, but the ultimate cause of this response may be the

evolutionary Evolution is change in the heredity, heritable Phenotypic trait, characteristics of biological populations over successive generations. These characteristics are the Gene expression, expressions of genes, which are passed on from parent to ...

advantage offered by stimulus filtering. An animal that saves energy by not responding to unnecessary stimuli may have increased fitness, which means that it would be able to produce more offspring, whereas an animal that does not filter stimuli may have reduced fitness due to depleted energy stores. An animal that practices stimulus filtering may also be more likely to respond appropriately to serious threats than an animal that is distracted by unimportant stimuli.

Physiological mechanism

When particular signals are received by the animal, the superior-ranking

neurons A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

determine which signals are important enough to preserve and which signals are insignificant and can be ignored. This process essentially works as a filter as the

synapses In the nervous system, a synapse is a structure that permits a neuron (or nerve cell) to pass an electrical or chemical signal to another neuron or to the target effector cell. Synapses are essential to the transmission of nervous impulses from ...

of the

neural network A neural network is a network or circuit of biological neurons, or, in a modern sense, an artificial neural network, composed of artificial neurons or nodes. Thus, a neural network is either a biological neural network, made up of biological ...

enhance certain signals and repress others, with simple stimuli receiving attention from lower-level neurons, and more complicated stimuli receiving attention from higher level neurons.

Relation to humans

Stimulus filtering is also seen in humans on a day-to-day basis. The

cocktail party effect The cocktail party effect is the phenomenon of the brain's ability to focus one's auditory attention on a particular stimulus while filtering out a range of other stimuli, such as when a partygoer can focus on a single conversation in a noisy room ...

refers to the situation where people in a crowded room tend to ignore other conversations and just focus on the one they are participating in. This effect also works in that when an individual hears their name in another's conversation they immediately focus on that conversation.

Examples

Moths

The evolution of a

moth Moths are a paraphyletic group of insects that includes all members of the order Lepidoptera that are not butterflies, with moths making up the vast majority of the order. There are thought to be approximately 160,000 species of moth, many of w ...

’s auditory system has helped them escape a

bat Bats are mammals of the order Chiroptera.''cheir'', "hand" and πτερόν''pteron'', "wing". With their forelimbs adapted as wings, they are the only mammals capable of true and sustained flight. Bats are more agile in flight than most bi ...

’s echolocation. Physically a moth has two ears on each side of the

thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...

where they receive ultrasonic indicators to hear the distinct vocalizations that then vibrate the membranes of the moths ears at one of two auditory receptors: A1 or A2. These are attached to the tympanum in the ear. Intense sound pressure waves sweep over the moth's body causing the tympanum to vibrate and deforming these receptor cells. This opens stretch-sensitive channels in the

cell membrane The cell membrane (also known as the plasma membrane (PM) or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of all cells from the outside environment ( ...

and provides the effective stimuli for a moth auditory receptor. These receptors work in the same ways that most

neuron A neuron, neurone, or nerve cell is an electrically excitable cell that communicates with other cells via specialized connections called synapses. The neuron is the main component of nervous tissue in all animals except sponges and placozoa. N ...

s do, by responding to the energy contained in selected stimuli and changing the permeability of their cell membranes to positively charged ions. Even though the A1 and A2 receptors work in a similar fashion, there are significant differences between them. The A1 receptor is the main bat detector, and as the rate of firing increases the moth turns away from the bat to reduce sonar echo. In other words, the A1 receptor is sensitive to low frequencies. To determine the relative position of the bat the differential firing rates of the A1 cells will fire on either side of the moth's head and if the bat is farther away cells receive a weaker signal and will fire at a slower rate. The A2 receptor is the emergency back-up system by initiating erratic flight movements as a last-ditch effort to evade capture. This differential sensitivity of the A1 and A2 sensory neurons leads to stimulus filtering of the bat vocalizations. Long-distance evasion tactics are engaged when the bat is far away and therefore the A1 sensory neurons fire. When the bat is in extremely close range, short-distance evasion tactics are engaged with the use of A2 sensory neurons. The adaptive value of the physiological mechanisms of two distinct receptors aids in the evasion of capture from bats.

Parasitoid flies

Female flies of the genus ''

Ormia ochracea ''Ormia ochracea'' is a small yellow nocturnal fly in the family Tachinidae. It is notable for its parasitism of crickets and its exceptionally acute directional hearing. The female is attracted to the song of the male cricket and deposits larvae ...

'' possess organs in their bodies that can detect frequencies of

cricket Cricket is a bat-and-ball game played between two teams of eleven players on a field at the centre of which is a pitch with a wicket at each end, each comprising two bails balanced on three stumps. The batting side scores runs by striki ...

sounds from meters away. This process is important for the survival of their species because females will lay their first

instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...

larvae into the body of the cricket, where they will feed and molt for approximately seven days. After this period, the larvae grow into flies and the cricket usually perishes. Researchers were puzzled about how precise hearing ability could arise from a small ear structure. Normal animals detect and locate sounds using the

interaural time difference The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound s ...

(ITD) and the

interaural level difference Sound localization is a listener's ability to identify the location or origin of a detected sound in direction and distance. The sound localization mechanisms of the mammalian auditory system have been extensively studied. The auditory system us ...

(ILD). The ITD is the difference in the time it takes sound to reach the ear. ILD is the difference in sound intensity measure between both ears. At maximum, the ITD would only reach about 1.5 microseconds and the ILD would be less than one decibel. These small values make it hard to sense the differences. To solve these issues, researchers studied the mechanical aspects of flies’ ears. They found that they have a presternum structure linking both tympanal membranes that is critical in detecting sound and localization. The structure acts as a lever by transferring and amplifying vibrational energy between the membranes. After sound hits the membranes at different amplitudes, the presternum sets up symmetrical vibration modes through bending and rocking. This effect helps the nervous system distinguish which side the sound is coming from. Because the presternum acts as an intertympanal bridge, the ITD is increased from 1.5 us to 55 us and the ILD is increased from less than one decibel to over 10 decibels. When looking at the nervous systems of flies, researchers found three auditory afferents. Type one fires only one spike to the stimulus onset, has low jitter (variability in timing over stimulus presentations), no spontaneous activity, and is the most common type. Type two fires two to four spikes to the stimulus onset, has increased jitter with subsequent spikes, and has low spontaneous activity. Finally, type three has tonic spiking to the presented stimulus, has low jitter only with the first spikes, has low spontaneous activity, and is the least common type. Researchers discovered that neurons responded the strongest to sound frequencies between 4 and 9 kHz, which includes the frequencies present in cricket songs. Also, neurons were found to have responded strongest at 4.5 kHz, which is the frequency of the Gryllus song. Despite the type of auditory afferent, all observed neurons revealed an inverse/latency relationship. The stronger the stimulus, the shorter the time until the neuron begins to respond. The difference in the number of afferents above the threshold on a side of the animal is called

population code Neural coding (or Neural representation) is a neuroscience field concerned with characterising the hypothetical relationship between the stimulus and the individual or ensemble neuronal responses and the relationship among the electrical activity o ...

and can be used to account for sound localization.

Midshipman fish

Female

midshipman fish A midshipman fish is any species of toadfish belonging to the genus ''Porichthys'' (in family Batrachoididae). Midshipman fish are distinguished by their photophores (organs which attract prey and after which they are named, being said to resembl ...

undergo stimulus filtering when it comes time to mate with a male. Midshipman fish use stimulus filtering when listening to sounds produced by underwater species. Dominant signals underwater range between 60–120 Hz, which is the most normally the most sensitive to the fish's auditory receptor. However, the female auditory system changes seasonally to acoustical stimuli in the songs of male midshipman fish. In the summer when female midshipman fish are reproducing they listen to a male humming song that can be produce a frequency level of 400 Hz. The summer is reproducing season for the females so their hearing is more sensitive to the high frequency of the male humming.

References

{{Reflist, refs= Alcock, J. (2009). ''Animal Behavior'' (Ninth ed., Vol. 1). Sunderland, MA: Sinauer Associates, Inc. Alderks, P. W., & Sisneros, J. A. (2011).
"Ontogeny of auditory saccular sensitivity in the plainfin midshipman fish, ''Porichthys notatus''."
''J Comp Physiol A'', 127, 387-398. {{cite web, url=http://nelson.beckman.illinois.edu/courses/neuroethol/models/fly_hearing/fly_hearing.html , title=Neuroethology: Fly Hearing , publisher=Nelson.beckman.illinois.edu , date=2003-04-29 , accessdate=2015-02-25 {{cite web, url=http://www.oxfordreference.com/view/10.1093/acref/9780198607212.001.0001/acref-9780198607212-e-367 , title=Stimulus filtering , publisher=Oxford Reference , date=2012-02-17 , accessdate=2015-02-25 {{cite web, author=Michael L. Oshinsky1 and Ronald R. Hoy2 , url=http://www.jneurosci.org/content/22/16/7254.full , title=Physiology of the Auditory Afferents in an Acoustic Parasitoid Fly , publisher=Jneurosci.org , date=2002-08-15 , accessdate=2015-02-25 {{cite web, url=http://bio.research.ucsc.edu/~barrylab/classes/animal_behavior/PREDATOR.HTM , title=Predator and Prey Interactions, Sinervo©1997 , publisher=Bio.research.ucsc.edu , date= , accessdate=2015-02-25 {{cite web, url=http://ebooks.cambridge.org/chapter.jsf?bid=CBO9781139164269&cid=CBO9781139164269A047 , title=5 - Stimulus filtering: vision and motion detection - University Publishing Online , publisher=Ebooks.cambridge.org , date= , accessdate=2015-02-25