Dec. 6, 2006 — What do dog barks have in common with bird tweets and human baby cries? All appear to communicate basic emotions, such as fear, aggression and submission, in somewhat the same acoustic way, according to a new Applied Animal Behavior Science study that suggests a primitive communication system may unite virtually all mammals.
The theory could help explain why previous research has found that many mammals, including humans, understand the vocalizations of different species.
For example, a Language Communication study determined young children can identify simple emotions conveyed in macaque calls. Other studies indicate that interacting individuals among African grey parrots and bonobos can agree on the object that’s likely referred to by a vocalization.
For the recent research, Péter Pongrácz and colleagues studied how well people with varying dog experience could describe several artificially assembled bark sequences. The barks, which were based on sounds made by a Mudi (a Hungarian herding dog), covered five emotional states: aggressiveness, fear, despair, playfulness and happiness.
Pongrácz, a professor of ethology at Eötvös Loránd University in Budapest, Hungary, and his team then compared the listeners’ answers to the acoustical features of the barks.
The scientists discovered that changes in three basic sound qualities — tone, pitch, and the time between barks — determined how listeners perceived the barks. In general, high-pitched barks with longer intervals between each bark were rated as less aggressive than lower-pitched barks heard in frequent succession.
Human babies vary similar sound quality characteristics when they cry, except frequency range appears to be more important than pitch when they express their needs.
This link between pitch or frequency and perceived emotion appears to carry across many different species, according to Pongrácz, who cited an earlier theory proposed by avian expert Eugene Morton.
"His basic argument was that, according to the general physical laws, larger bodies emit sounds characterized by lower frequencies — and these are also noisier/atonal, thus receivers can predict the size of the sender," Pongrácz and his team wrote.
"This relationship could have formed the basis of an evolutionary ritualization process whereby low pitched vocalizations tended to signal aggression because larger animals are more likely to win contests...and high pitched vocalizations became predictors of submission or friendly intent."
