Back at the lab, Branje plays me another tune. This one is slow and starts very low along my back. It clearly feels sad. The tunes were composed on Branje’s keyboard, which doesn’t look much like a normal keyboard. It is large and shaped like a semicircle so that composers can always feel the pulse against their back. The keys themselves are divided up into five sections, each of which map to different sets of voice coils in the Emoti-Chair, and each section has eight keys ranging from 40 to 421 hertz. So if Branje taps the 40-hertz key at the left-most section of the keyboard, a person sitting in the chair would feel a low-pitched buzz along their lower back. If Branje hits the same 40-hertz key on the far right of the keyboard, that same buzz would play along the shoulder blades.

Once he had created a prototype for the keyboard, Branje set out to see how he could convey the emotion typically found in music through touch. Some aspects of music, Branje says, transfer perfectly from ear to skin, such as rhythm and tempo, though he suspected other elements would prove more challenging. For instance, in Western music, major keys connote happiness, while minor keys connote sadness. But what would the equivalent of songs written in major and minor keys feel like? It’s a black box, Branje says. “There is no such thing as a vibrotactile song.”

To begin sorting it out, Branje asked professional music composers to write happy or sad vibrotactile songs. Someone who had spent years conveying emotion via sound might intuitively understand how to convey those same feelings through touch, he reasoned.

His early results are promising. When Branje played those compositions to volunteers and had them report what emotion they thought the songs conveyed, they often reached the same conclusion. Branje then broke down each composition by musical elements, such as tempo, amplitude, frequency, length of individual notes, and how often a piece jumped along tracks (or speakers along the back). He found that tempo, or the number of notes per second, and frequency had the greatest significance. “If you use a higher frequency and a higher tempo people are going to think your songs are happier,” he says.

Aldous Huxley, as usual, has the matter well in hand. In his 1932 masterpiece Brave New World, he describes the feelies:

"Going to the Feelies this evening, Henry?" enquired the Assistant Predestinator. "I hear the new one at the Alhambra is first-rate. There's a love scene on a bearskin rug; they say it's marvelous. Every hair of the bear reproduced. The most amazing tactual effects..."

"Take hold of these knobs on the arms of your chair," whispered Lenina. "Otherwise, you won't get any of the feely effects."
(Read more about Aldous Huxley's feelies)