On February 1st, the BBC radio 4 Today programme presenter John Humphrys asked Professor Bob Knight of UC Berkeley whether the results of Knight’s recent experiment into the reconstruction of speech from neuron signals could possibly lead to the danger of those with ‘malign intent to find out what we’re thinking – I’m thinking a Dr. Strangelove scenario here’. Humphrys, quite rightly, mitigated the question with a snort and a chuckle, a telling admission of the absurdity of his question. He missed the chance to highlight a valid concern about Knight’s research, one that could scupper the chances of millions of people with motor conditions such as motor neurone disease or dysarthria from making their intended speech known to others.
Knight’s work, Reconstructing Speech from Human Auditory Cortex (Pasley et al.) was published in PLoS Biology on January 31st. In the paper, the authors succeed in translating the neuron responses in the brain’s Superior Temporal Gyrus (STG) into prosthetic reconstructed speech. They do this by analysing signals from electrode arrays that were attached to patients’ brains during epilepsy surgery. The patients are played recordings of words and the arrays then receive feedback of that word. The neuron signals from that feedback are then translated into prosthetic speech. Importantly, thus far, the authors have only created speech from feedback – that is the brain’s acknowledgement of the word it has heard, not the intended speech of the person. However, it is ground-breaking work that could pave the way for sufferers of motor and speech disorder to one day communicate through a prosthetic speech apparatus by simply thinking of words.
The leap from reconstructing feedback to constructing intended speech is the challenge that lies ahead for scientists. To overcome this challenge, an important distinction that researchers need to establish is the difference between inner speech and intended speech. For normal speakers, intended speech is everything that is articulated. We, however, produce inner speech far more regularly, to read, write, think, regulate our thoughts and behaviour, perhaps even to help liberate repressed thoughts.
For the purpose of prosthetic speech construction, the relationship between separate brain areas that affect decision making needs to be understood. Currently there would be no way to be sure that the prosthetic device would translate neuron signals from intended speech rather than from inner speech: in the miracle that would give motor neuron disease sufferers a voice, an unacceptable side effect would be the prescription of Tourette’s.
Scientists are unable to clearly describe the mental architecture of decision making. Two major brain areas have been identified but it is not yet certain how these areas work together to enable a decision. It is unclear what kind of advances will be made in identifying the exact nature of decision making before the technology to construct speech from thoughts has been developed. But if this distinction isn’t established, we would be consigning motor disorder sufferers to a life without free linguistic choice.
Experiments such as Benjamin Libet’s free-will experiments have shown that a ‘normally’ functioning speaker is one who is able to select an appropriate speech act from the possible speech acts available to him or her. These decisions are based on context, speaker bias, experience of previous, similar choices, emotion, morals etc. The logic then runs that in order to select the act that is most appropriate for the context, we must veto various other possible acts. This tells us a lot about how some disorders operate, notably Tourette’s. Tourette’s sufferers lack the control of the ability to veto acts and therefore produce unintended acts, such as speech, noises and tics.
If the activity of the brain’s decision making process isn’t better understood, the motor disorder sufferer with prosthetic speech, like the Tourette’s sufferer, will be consigned to a life without free will and free choice. It is here and in his reference to Dr Strangelove that the BBC’s John Humphrys did get something right- Dr Strangelove had an anarchic right hand that was a metaphor for the Nazi ‘brainwashing’ of German people. The phenomenon of anarchic hand syndrome is very real. It is a condition whereby one hand listens to the brain’s intentions to act while the other is entirely uncontrollable. And is another example of the brain being unable to veto an act. Humphrys though, caught up in science fiction, failed to ask the more pertinent question: would prosthetic speech production reveal the unvetoed inner thoughts of a person rather than just the consciously-decided speech acts? After such an incredible technological and medical breakthrough, this is one of the most important questions that researchers must next ponder.