The Sensor Chair
The Sensor Chair was designed in the Fall of 1994 for a new mini-opera,
entitled Media/Medium, which Tod Machover composed for the magicians
Penn & Teller. The trick starts with
performance by Penn on this new "magical" instrument. In the show, after
performing this "sensor solo," Penn explains how it works to the audience, and
then explains how such technology would have been very useful 100 years ago to
measure such invisible and ineffable things as ghosts and spirits. This leads
to a wild exploration, through music and magic, of the fine line between
state-of-the-art technology and "magic," and between the performance bravura of
entertainment and the cynical fakery of mystics and mediums.
A rather large team worked on the project, including Pete Rice and Eran Egozy
for software, and Joe Paradiso, Neil Gershenfeld and Ed Hammond for hardware.
The person seated in the chair becomes an extension of a transmitting antenna
placed in the chair cushion. antenna; and their body acts as a conductor which
is capacitively coupled into the transmitter plate. Four receiving antennas
are mounted at the vertices of a square, on poles placed in front of the
chair. These pickups receive the transmitted signal with a strength that is
determined by the capacitance between the performer's body and the sensor
antenna. As the seated performer moves his hand forward, the intensities of
these signals are thus a function of the distances between the hand and
corresponding pickups. The pickup signal strengths are digitized and sent to
a Macintosh computer, which estimates the hand position. A pair of pickup
antennas are also mounted on the floor of the chair platform, and are used to
similarly measure the proximity of left and right feet, providing a set of
pedal controllers. Therefore, all movements of the arms and upper body are
measured very accurately, and turned into different kinds of music depending
on the state of the Hyperlisp software.
Read a technical description of
the Sensor Chair hardware, written by Joseph Paradiso.
See a photograph of the Sensor
Chair prototype, which will be used in the Brain Opera performances at