A supernormal stimulus or superstimulus is an exaggerated version of a stimulus to which there is an existing response tendency, or any stimulus that elicits a response more strongly than the stimulus for which it evolved. For example, it is possible to create artificial bird eggs which certain birds will prefer over their own eggs, particularly evident in brood parasitism. Some speculate humans can be similarly exploited by junk food and pornography. Organisms tend to show a preference for the stimulus properties (e.g. size, colour, etc.) that have evolved in nature, but when offered an artificial exaggerated stimulus, animals will show behaviour in favour of the artificial stimulus over the naturally occurring stimulus. A variety of organisms display or are susceptible to supernormal stimuli, including insects, birds, and humans. Supernormal stimuli are present in areas of biology and psychology, but are also studied within other fields like sociology and art. British academic Nigel Spivey demonstrates the effect in the first episode of the 2005 BBC documentary series How Art Made the World to illustrate neuroscientist Vilayanur S. Ramachandran's speculation that this might be the reason for the exaggerated body image demonstrated in works of art from the Venus of Willendorf right up to the present day.
Causation Animals exhibiting, or responding to, characteristics that represent a supernormal stimulus usually display them as a result of selective pressures. Co-evolution between animals displaying supernormal stimuli, and the organisms responding to the supernormal stimuli, rely on evolution and propagation of genetics, behavioral patterns, and other biological factors. Supernormal stimuli such as emphasized color, size, patterns, or shapes, are often successful because an organism that exhibits them will often be selected by an organism that favors it. This will ensure survival and increased reproductive fitness of current and later generations.
In biology In the 1950s, Konrad Lorenz observed that birds would select brooding eggs that resembled those of their own species but which were larger. Niko Tinbergen, coined this term through his research, which discovered that experimenters could display an alternate target that attract an organism's attention more so than the naturally occurring target. Tinbergen studied herring gulls, and found the chicks peck at the red spot located on their parent's bill. The offspring targets the red spot due to the contrast of color (stimulus). They do this in order to receive food through regurgitation from the parent. Tinbergen and colleagues developed an experiment that presented different models to chicks and determined their pecking rates. They used different models including an adult herring gull's natural head, a standard wooden model of its head, the bill only, and a red stick with smaller white markings on it. The pecking rate of the chicks were consistent with the natural head, standard head model, and the bill only model. The pecking rate of the chicks increased when presented with the stick model. This suggests that the chicks preferred the dramatic contrast of the red stick with the yellow markings, therefore the artificial stimulus of the stick model was favored over the basic herring gull head and bill models, proving that the artificial stimuli was favored over the naturally occurring stimuli. Following his extensive analysis of the stimulus features that elicited food-begging in the chick of the herring gull, he constructed an artificial stimulus consisting of a red knitting needle with three white bands painted around it; this elicited a stronger response than an accurate three-dimensional model of the parent's head (white) and bill (yellow with a red spot). Tinbergen and his students studied other variations of this effect. He experimented with dummy plaster eggs of various sizes and markings finding that most birds preferred ones with more exaggerated markings than their own, more saturated versions of their color, and a larger size than their own. Small songbirds which laid light blue grey-dappled eggs preferred to sit on a bright blue black polka-dotted dummy so large they slid off repeatedly. Territorial male stickleback fish would attack wooden floats with red undersides—attacking them more vigorously than invading male sticklebacks if the underside were redder. Lorenz and Tinbergen accounted for the supernormal stimulus effect in terms of the concept of the innate releasing mechanism; however this concept is no longer widely used. The core observation that simple features of stimuli may be sufficient to trigger a complex response remains valid, however. In 1979, the term supernormal stimulus was used by Richard Dawkins and John Krebs to refer to the exaggeration of pre-existing signs induced by social parasites, noting the manipulation of baby birds (hosts) from these, to illustrate the effectiveness of those signals. In 1983, entomologists Darryl Gwynne and David Rentz reported on the beetle Julodimorpha bakewelli attempting to copulate with discarded brown stubbies (a type of beer bottles) studded with tubercules (flattened glass beads). This work won them the 2011 Ig Nobel Prize in biology. Another example of this is the study made by Mauck and colleagues, where they evaluated the effects of a plant pathogen named cucumber mosaic virus or CMV. This study showed that the aphids preferred the healthy plants but are still attracted by the infected plants, because of the manipulation of volatile compounds used by plants to attract them.
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