cave art
October 29, 2014

Prehistoric Art And Auditory Illusions Of The Supernatural

April Flowers for redOrbit.com - Your Universe Online

Prehistoric art can be found around the world. Early man painted cave walls in France, carved petroglyphs in Arizona and erected huge monuments in England, just to name a few. A new study, which will be presented this week at the 168th Meeting of the Acoustical Society of America (ASA), reveals that some of these artistic endeavors might have been inspired by the behaviors of sound waves being misinterpreted as "supernatural."

"Ancient mythology explained echoes from the mouths of caves as replies from spirits, so our ancestors may have made cave paintings in response to these echoes and their belief that echo spirits inhabited rocky places such as caves or canyons," explained Steven J. Waller, of Rock Art Acoustics. Waller will describe several ways virtual sound images and absorbers can appear supernatural during his presentation.

The reflection of light off of a silvered surface presents the illusion of being able to see yourself duplicated, such as in a mirror or a still body of water. Sound waves reflect as well. Scientists have shown that sound waves reflecting off a surface are mathematically identical to sound waves emanating from a virtual sound source behind a reflecting pane such as a large cliff face. "This can result in an auditory illusion of somebody answering you from within the rock," Waller said.

Hoof beats and the echoes of clapping can sound eerily similar, and multiple echoes within a cavern can blend into a thunderous reverberation, mimicking the sound of a stampeding herd of hoofed animals.

"Many ancient cultures attributed thunder in the sky to 'hoofed thunder gods,' so it makes sense that the reverberation within the caves was interpreted as thunder and inspired paintings of those same hoofed thunder gods on cave walls," said Waller. "This theory is supported by acoustic measurements, which show statistically significant correspondence between the rock art sites and locations with the strongest sound reflection."

Waller believes that ancient cultures could have misinterpreted other acoustical characteristics, as well. He noticed a resemblance between Stonehenge and an interference pattern. To test this, he created an interference pattern in an open field using two flutes "droning the same note."

"The quiet regions of destructive sound wave cancellation, in which the high pressure from one flute cancelled the low pressure from the other flute, gave blindfolded subjects the illusion of a giant ring of rocks or 'pillars' casting acoustic shadows," Waller said.

Then he demonstrated that Stonehenge radiates acoustic shadows that recreate the same pattern as interference. "My theory that musical interference patterns served as blueprints for megalithic stone circles—many of which are called Pipers' Stones—is supported by ancient legends of two magic pipers who enticed maidens to dance in a circle and turned them all into stones," Waller noted.

The study findings have significant implications, chiefly in demonstrating that acoustical phenomena were culturally significant to early humans. This suggests that the natural soundscapes of archaeological sites should be preserved for further study.

"Even today, sensory input can be used to manipulate perception and lead to illusions inconsistent with scientific reality, which could have interesting practical applications for virtual reality and special effects in entertainment media," Waller said. "Objectivity is questionable, because a given set of data can be used to support multiple conclusions."

The history of our species is full of such misinterpretations, such as the much more recent belief that the sun traveled around the Earth. "Sound, which is invisible and has complex properties, can easily lead to auditory illusions of the supernatural," he added. "This, in turn, leads to the more general question: what other illusions are we living under due to other phenomena that we are currently misinterpreting?"

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