“We could start below that.” He noted, for
instance, that it does not require a terri-
bly complicated message to call for an air
strike or a missile launch: “;at would be a
very nice operational capability.”
The relative ease with which ;;; can
be applied comes at a price, however. ;e
exact location of neural activity is far more
di;cult to discern via ;;; than with many
other, more invasive methods because the
skull, scalp, and cerebral ;uid surrounding
the brain scatter its electric signals before
they reach the electrodes. That blurring
also makes the signals harder to detect at
all. ;e ;;; data can be so messy, in fact,
that some of the researchers who signed
on to the project harbored private doubts
about whether it could really be used to
extract the signals associated with unspo-
ken thoughts.
I;; ;;; ;;;;;;; ;;;;;; ;; ;;; ;;;;;;;, back in ;;;;, one of D’Zmura’s key col- laborators, renowned neuroscientist David Poeppel, sat in his office on the second ;oor of the New York University psychology building and realized he was unsure even where to begin. With his research partner
Greg Hickok, an expert on the neuroscience
of language, he had developed a detailed
model of audible speech systems, parts of
which were widely cited in textbooks. But
there was nothing in that model to suggest
how to measure something imagined.
For more than ;;; years, Poeppel re;ect-ed, speech experimentation had followed
a simple plan: Ask a subject to listen to a
speci;c word or phrase, measure the subject’s response to that word (for instance,
how long it takes him to repeat it aloud),
and then demonstrate how that response
is connected to activity in the brain. Trying to measure imagined speech was much
more complicated; a random thought
could throw o; the whole experiment. In
fact, it was still unclear where in the brain
researchers should even look for the relevant signals.
Solving this problem would call for a new
experimental method, Poeppel realized.
He and a postdoctoral student, Xing Tian,
decided to take advantage of a powerful
imaging technique called magnetoenceph-alography, or ;;;, to do their reconnaissance work. ;;; can provide roughly the
same level of spatial detail as ;;o; but with-
“Show us the evidence that
this could really work—that you
are not just hallucinating it,”
the Army asked Schmeisser.
out the need to remove part of a subject’s
skull, and it is far more accurate than ;;;.
Poeppel and Tian would guide subjects
into a three-ton, beige-paneled room constructed of a special alloy and copper to
shield against passing electromagnetic
;elds. At the center of the room sat a one-ton, six-foot-tall machine resembling a
huge hair dryer that contained scanners
capable of recording the minute magnetic
fields produced by the firing of neurons.
After guiding subjects into the device, the
researchers would ask them to imagine
speaking words like athlete, musician, and
lunch. Next they asked them to imagine
hearing the words.
When Poeppel sat down to analyze the
results, he noticed something unusual. As
a subject imagined hearing words, his auditory cortex lit up the screen in a characteristic pattern of reds and greens. ;at part was
no surprise; previous studies had linked the
auditory cortex to imagined sounds. However, when a subject was asked to imagine
speaking a word rather than hearing it, the
auditory cortex ;ashed an almost identical
red and green pattern.
Poeppel was initially stumped by the
results. “That is really bizarre,” he recalls
thinking. “Why should there be an auditory
pattern when the subjects didn’t speak and
no one around them spoke?” Over time he
arrived at an explanation. Scientists had long
been aware of an error-correction mechanism in the brain associated with motor
commands. When the brain sends a command to the motor cortex to, for instance,
reach out and grab a cup of water, it also
creates an internal impression, known as an
e;erence copy, of what the resulting movement will look and feel like. ;at way, the
brain can check the muscle output against
the intended action and make any necessary corrections.
Poeppel believed he was looking at an
efference copy of speech in the auditory
cortex. “When you plan to speak, you acti-
vate the hearing part of your brain before
you say the word,” he explains. “Your brain
is predicting what it will sound like.”
;e potential signi;cance of this ;nding
was not lost on Poeppel. If the brain held
on to a copy of what an imagined thought
would sound like if vocalized, it might be
possible to capture that neurological record
and translate it into intelligible words. As
happens so often in this ;eld of research,
though, each discovery brought with it a
wave of new challenges. Building a thought
helmet would require not only identifying
that e;erence copy but also ;nding a way
to isolate it from a mass of brain waves.
;’;;;;; ;;; ;;; ;;;; ;; ;; ;;;;;; ;;;;
spent the past two years taking baby steps
in that direction by teaching pattern recognition programs to search for and recognize speci;c phrases and words. ;e sheer
size of a ;;; machine would obviously
be impractical in a military setting, so the
team is testing its techniques using lightweight ;;; caps that could eventually be
built into a practical thought helmet.
The caps are comfortable enough that
Tom Lappas, a graduate student working
with D’Zmura, often volunteers to be a
research subject. During one experiment last
November, Lappas sat in front of a computer
wearing ;ip-;ops, shorts, and a latex ;;;
cap with ;;; gel-soaked electrodes attached
to it. Lappas’s face was a mask of determined focus as he stared silently at a screen
while military commands blared out of a
nearby speaker.
“Ready Baron go to red now,” a recorded
voice intoned, then paused. “Ready Eagle go
to red now…Ready Tiger go to green now...” As
Lappas concentrated, a computer recorded
;;;;;;;;; ;; ;;;; ;;
