Decoding Human Speech: Promise for Locked-in Syndrome
Date: 22/08/2012 |
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Researchers from Technion and from UCLA have identified a structured neuronal encoding and decoding of human speech features. They were able to directly decode vowels from the neural activity which leads to their articulation - a finding which could allow individuals who are completely paralyzed or "locked in" to "speak" to the people around them through a direct brain-computer interface.
Human speech sounds are produced through a coordinated movement of structures along the vocal tract. In the scientific article just published in Nature Communications, the researchers -- Prof. Shy Shoham of the Faculty of Biomedical Engineering, Dr Ariel Tankus, and Prof. Itzhak Fried of the Department of Neurosurgery, University of California, Los Angeles, and of Tel-Aviv University -- showed highly structured neuronal encoding of vowel articulation. According to the researchers, at the neuronal population level, a decoding analysis reveals that the underlying structure of vowel encoding reflects the anatomical basis of articulatory movements. This structured encoding enables accurate decoding of volitional speech segments and could be applied in the development of brain–machine interfaces for restoring speech in paralysed individuals.
"There are diseases in which the patient's entire body is paralyzed, he is effectively 'locked in' (locked-in syndrome) and is unable to communicate with the environment, but his mind still functions," explains Shoham, head of the Neural Interface Engineering Laboratory. "Our long-term goal is to restore these patients' ability to speak using systems that will include implanting electrodes in their brains, decoding the neural activity that encodes speech, and 'voicing' artificial speech sounds. For this purpose, we wanted to first understand how the information about the articulated syllable is encoded in the electrical activity of an individual brain neuron and of a neuron population. In our experiments we identified cell populations that distinctly participate in the representation. For example, cells we registered in an area in the medial frontal lobe that includes the anterior cingulate cortex, surprised us in the manner in which they 'sharply' represented certain vowels but not others, even though the area is not necessarily known as having a major role in the speech generation process".
The experiments were conducted in the UCLA Medical Center with the participation of epilepsy patients, in whose brains Prof. Fried and his team implanted depth electrodes. Tankus, who was a postdoctoral fellow at UCLA and is now a researcher in Shoham's lab at the Technion, asked the patients to articulate vowels as well as syllables comprising a consonant and a vowel, and recorded the resulting neuronal activity in their brain. The researchers discovered two neuron populations that encode the information about the vowel articulated in an entirely different way.
Tankus explains,"We have developed a new algorithm that improved greatly the ability to identify from brain activity which syllable was articulated, and this algorithm has allowed us to obtain very high identification rates. Based on the present findings, we are currently conducting experiments toward the creation of a brain-machine interface that will restore people's speech faculties."
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