Near-Infrared Tool Shows Reading Helps Disabled Children

In a study published in the February 2009 issue of The Journal of Neural Engineering, Bloorview Kids Rehab (Toronto, Canada), scientists demonstrated the ability to decode an individual's preference for one of two drinks with 80% accuracy by measuring the intensity of near-infrared light absorbed in brain tissue.

"This is the first system that decodes preference naturally from spontaneous thoughts,” said Sheena Luu, a University of Toronto (Canada) Ph.D. student in biomedical engineering who led the study under the supervision of Dr. Tom Chau, Canada research chair in pediatric rehab engineering.

Most brain-computer interfaces designed to read thoughts require training. For example, in order to indicate yes to a question, the person needs to do an unrelated mental task-- such as singing a song in their head. The nine adults in Dr. Luu's study received no training. Prior to the study they rated eight drinks on a scale of one to five.

Near-infrared spectroscopy (NIRS) has recently been identified as a safe, portable, and relatively low-cost signal acquisition tool for noninvasive brain-computer interface (BCI) development. The ultimate goal of BCI research is for the user to be able to communicate functional intent directly through thoughts. The researchers propose a NIRS-BCI paradigm based on directly decoding neural correlates of decision-making, specifically subjective preference evaluation. Nine subjects were asked to mentally evaluate two possible drinks and decide which they preferred. Frequency domain near-infrared spectroscopy was used to image each subject's prefrontal cortex during the task. Using mean signal amplitudes as features and linear discriminant analysis, the investigators were able to decode which drink was preferred on a single-trial basis with an average accuracy of 80%.

Wearing a headband fitted with fiberoptics that emit light into the pre-frontal cortex of the brain, the study participants were shown two drinks on a computer monitor, one after the other, and asked to make a mental decision about which they liked more. "When your brain is active, the oxygen in your blood increases and depending on the concentration, it absorbs more or less light,” Dr. Luu commented. "In some people, their brains are more active when they don't like something, and in some people they're more active when they do like something.”

After teaching the computer to recognize the unique pattern of brain activity associated with preference for each subject, the researchers accurately predicted which drink the participants liked best 80% of the time. "Preference is the basis for everyday decisions,” Dr. Luu remarked. When children with disabilities cannot speak or gesture to control their environment, they may develop a learned helplessness that impedes development.

In the future, Dr. Luu envisions creating a portable, near-infrared sensor that rests on the forehead and relies on wireless technology, opening up the world of choice to children who cannot speak or move. Her study is part of Dr. Chau's body-talk research, which aims to give children who are "locked in” by disability a way to express themselves through subtle body processes like breathing pattern, heart rate and brain activity.

Dr. Luu noted that the brain is too complicated to ever allow decoding of an individual's random thoughts. "However, if we limit the context--limit the question and available answers, as we have with predicting preference--then mind-reading becomes possible.”

Bloorview Kids Rehab is Canada's largest children's rehabilitation hospital, affiliated with the University of Toronto.

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