The Aztec skull whistle sounded like people screaming

A new study by researchers at the University of Zurich published in the journal Communications Psychology has found that the scream-like sounds of the Aztec skull whistle have a terrifying effect on human listeners today, reflected in their brain activity.

Aztec skull whistles were petite (3-5 cm) clay skulls with tubular stems often found at burial and human sacrifice sites dating to between 1250 and 1521. Archaeologists hypothesize that the skull iconography represents Ehecatl, the Aztec God of the Wind, who collected bones of previous eras in the underworld and created humankind with them. They may also refer to Mictlantecuhtli, Aztec god of the underworld, and the screaming sound they generated may have prepared the sacrifice victim for their descent into the underworld, perhaps the fifth level which is filled with painful, howling winds. Another hypothesis is that the instrument was simply mimicking human screams as a component of the sacrifice ritual.

Researchers sought to understand the possible symbolism of the skull whistle by studying its effect of the sounds they produce on human listeners. The study collected sound recordings from skull whistles excavated from temple precincts in Mexico City. They also made high-resolution CT scans of examples from the collection of the Ethnological Museum in Berlin that they then used to create 3D digital reconstructions of the originals as well as accurate, playable replicas. The digital models revealed new details on how the whistles generated sound.

Air was blown into a mouthpiece connected to an airduct that constricted at the far end where it connected to the interior of the skull. The rounded back of the skull was a counterpressure chamber where the air circulated before heading out a collision chamber to the bell and the whistle opening under the “jaw” of the skull.

The models revealed a unique internal construction of two opposing sound chambers that create physical air turbulence as the source of the screeching sound. “The whistles have a very unique construction, and we don’t know of any comparable musical instrument from other pre-Columbian cultures or from other historical and contemporary contexts,” says [University of Zurich neuroscience professor Sascha] Frühholz.

When test subjects heard the sound recordings of the death whistles, they identified them as human screams.

The Aztec death whistle sounds were also played to human listeners while their brains were being recorded. Brain regions belonging to the affective neural system responded strongly to the sound, again confirming its daunting nature. But the team also observed brain activity in regions that associate sounds with symbolic meaning. This suggests a “hybrid” nature of these death whistle sounds, combining a basic psychoaffective influence on listeners with more elaborate mental processes of sound symbolism, signifying the iconographic nature.

Music has always had strong emotional impact on human listeners in both contemporary and ancient cultures, hence its use in ritual religious and mythological contexts. Aztec communities may have specifically capitalized on the frightening and symbolic nature of the death whistle sound to influence the audience in their ritual procedures, based on the knowledge of how the sound affects modern humans. “Unfortunately, we could not perform our psychological and neuroscientific experiments with humans from ancient Aztec cultures. But the basic mechanisms of affective response to scary sounds are common to humans from all historical contexts,” says Frühholz.

Original skull whistle sound clip:

Replica skull whistle played with high air pressure:

Replica skull whistle played with high air pressure

* This article was originally published here