The term '''Signsign Stimulusstimulus''' also known as a '''[[:simple:Releaser|releaser]]''', is the determining feature of a stimulus that produces a response. Sign stimuli are often found when observing a fixed action pattern (FAP) whichthat is an innate behavior with very little variance in the manner in which the actions are executed. Several examples of sign stimuli can be seen through the observation of animal behavior in their natural environment. Experimenters have gone into these natural environments to better assess the stimuli and determine the key features of them that elicit a fixed action pattern. Scientists have also observed direct exploitation of sign stimuli in nature among different species of birds.
Fixed action patterns are released due to certain external stimuli.<ref name=":03"/> These stimuli are single or a small group of attributes of an object, not the object as a whole.<ref name=":3">{{Cite web |url=http://www.flyfishingdevon.co.uk/salmon/year1/psy128ethology_experiments/ethexpt.htm#FAP |title=Ethological studies of sign stimuli and motivation |website=www.flyfishingdevon.co.uk |access-date=2019-10-22}}</ref> These attributes may include color, shape, odor, and sound.<ref name=":03"/><ref name=":15"/>
Exaggerated models of these attributes are called [[Supernormal stimulus|supernormal stimuli]].<ref name=":4">{{Cite book |title=The herring gull's world; a study of the social behaviour of birds. |last=Tinbergen, Niko,1907-1988.|date=1953 |publisher=Collins |isbn=0002194449 |___location=London |oclc=1029697}}</ref> A supernormal stimulus leads to an exaggerated response.<ref name=":4" /> Supernormal stimuli are more effective at releasing a response than a natural stimulus.<ref name=":4" />
An external stimulus that elicits a fixed action pattern is termed a sign stimulus if the stimuli emanates from the environment.<ref name=":3" /> Whereas, a releaser emanates from one's own species.<ref name=":3" />
===Supernormal Stimulistimuli===
When conducting further experiments, scientists came across the idea of [[Supernormal stimulus|Supernormalsupernormal Stimulistimuli]]. A scientist by the name of [[Nikolaas Tinbergen|Tinbergen]] found that incubating geese when given the choice between performing the egg-rolling FAP with an egg versus a full-sized volleyball, they chose the volleyball. These supernormal stimuli, although not naturally occurring, gave insight into the process of natural selection and how it may be that some stimulus features such as the size of the egg result in and increased ability to trigger a FAP.<ref name=":0">{{cite book |last1=Gould |first1=James |title=Ethology: The Mechanisms and Evolution of Behavior |date=1983 |publisher=John Wiley & Sons Ltd}}</ref>
