right|thumb|150px|[[Venus of Willendorf, figurine exaggerating body and breast stimuli.]]
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. They do this in order to receive food through regurgitation from the parent.
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.
Insects
Pollinators, like butterflies, show behavioral response(s) to supernormal stimuli through intersexual communication. Butterflies use olfactory cues, but primarily rely on visual forms of communication, due to wind and temperature affecting their sense of smell.
Supernormal stimuli can be exhibited by brood parasites, for example, the parasitic cuckoo chick and parental care by reed warblers. Brood parasites have evolved more dramatic colors, sizes, patterns, and/or shapes that lead to the parasite being interpreted as healthier or more preferable, in contrast to neighboring offspring. Cuckoo chicks are often successful because their begging calls, the supernormal stimulus, are representative of an entire reed warbler brood. It can also be instinctual for certain species to select the supernormal stimuli that will suggest the best energy investment of the individual, often parental investment. she examines the impact of supernormal stimuli on the diversion of impulses for nurturing, sexuality, romance, territoriality, defense, and the entertainment industry's hijacking of our social instincts. In her earlier book Waistland, Also in a theoretical paper, Doyle proposed that how women walk creates supernormal stimuli through continuously alternating motion of the waist and hips causing peak shifts in perceptions of physical attractiveness involving women's waist-to-hip ratio. Furthermore, Pazhoohi et al. (2019) using eye tracking confirmed that lower than optimal waist-to-hip ratios are supernormal stimuli and they may generate peak shifts in responding.
Pascal Boyer has suggested that music is a superstimulus targeting human affinity for speech, and that symmetrical textile and building patterns are superstimuli targeted to the visual cortex.
In art
Costa and Corazza (2006), examining 776 artistic portraits covering the whole history of art, showed that eye roundness, lip roundness, eye height, eye width, and lip height were significantly enhanced in artistic portraits compared to photographic ones matched for sex and age. In a second study, forty-two art academy students were requested to draw two self-portraits, one with a mirror and one without (from memory). Eye and lip size and roundness were greater in artistic self-portraits. These results show that the exaggeration and "supernormalization" of key features linked to attractiveness, such as eye and lip size, are frequently found in art.
Pazhoohi et al. (2019) showed that classic contrapposto pose is considered more attractive and provided evidence and insight as to why, in artistic presentation, goddesses of beauty and love are often depicted in contrapposto pose.