For 2,500 years Andean civilizations produced earthenware whistling vessels. From Ecuador to southern Peru, Indian craftmen molded clay into vessels that have only recently been interpreted as specifically pitched whistles. The conclusion was made by Steven Garrett and Daniel Stat and was reported in 1977 in The Journal of the Acoustical Society of America. This acoustical analysis determined that each culture produced its own range of frequencies, with the tones being in the area of greatest sensitivity to human hearing. The acoustical study also determined that no single culture fabricated whistles in a range encompassing even half of an octave, indicating that the vessels, although intentionally made as whistles, were not intended as musical instruments - at least not in the usual sense. However, when several vessels from a specific culture are played simultaneously, a psycho-acoustical effect is created through the interaction of the different frequencies. Since this discovery, many modern people have experienced this effect when playing the vessels in small groups usually comprised of from four to seven persons. Often, the players have reported changes in their state of consciousness akin to the changes reported by practitioners of various meditation techniques. The most frequent response has been described as a centering of consciousness or Zen-like state of clarity.