By Chris Summers BBC News

A BBC reporter tries out a conventional lie detector

As the British government unveils plans to make lie detector tests mandatory for convicted paedophiles, some scientists in the US are working on more advanced technology which might be better equipped at detecting deception.

Imagine the Pentagon equipped with a machine which can read minds. Sound like the plot of a Hollywood thriller?

Well, it might not be that far away.

The US Department of Defense has given Dr Jennifer Vendemia a $5m grant to work on her theory that by monitoring brainwaves she can detect whether someone is lying.

She claims the system has an accuracy of between 94% and 100% and is an improvement on the existing polygraph tests, which rely on heart rate and blood pressure, respiratory rate and sweatiness.

Her system involves placing 128 electrodes on the face and scalp, which translate brainwaves in under a second. Subjects only have to hear interrogators' questions to give a response.

But the system has a long way to go before it replaces polygraphs, which were invented almost a century ago and remain a tried and tested system of deception detection.

Paedophile tests

On Thursday the UK government unveiled its Management of Offenders and Sentencing Bill.

POLYGRAPH PILOT AREAS West Midlands Thames Valley Northumbria Northamptonshire Greater Manchester London Leicestershire and Rutland Lancashire Devon and Cornwall Bedfordshire, Hertfordshire and Cambridgeshire

A key plank of the bill is increasing the use of polygraph tests for convicted paedophiles who have been released on licence.

A voluntary scheme has been running in 10 pilot areas in England since September 2003.

But under the new bill the tests will become compulsory for paedophiles in the 10 pilot areas.

They are asked whether they have had contact with children, while having their anxiety levels measured.

But some critics believe the polygraph is flawed.

"The idea with polygraphs is that there is a tell-tale physical response associated with deception and I just don't accept that is true.

"Even if it were true for the normal person then I don't think it's true for psychopaths, or others with mental abnormalities," says Steven Aftergood, of the Federation American Sciences.

The mouth may lie, but the face it makes nonetheless tells the truth Friedrich Nietzsche Philosopher

Mr Aftergood says he doesn't know about Dr Vendemia's invention but "if there was a machine which was able to read people's minds, it would give greater urgency to questions of people's privacy.

"In the United States it could even be unconstitutional because, under the Fifth Amendment, citizens have a right not to self-incriminate themselves."

In the US a specific piece of legislation, the Employee Polygraph Protection Law, forbids firms from using lie detectors to vet workers.

The one exception is the intelligence community, where polygraphs are a ubiquitous form of checking on existing and potential employees.

Dr Vendemia says her system would be an improvement on polygraphs.

"If you are examined by a good interrogator a polygraph will be 85 to 90% accurate," she says. "But others have less than 50% accuracy. My technology has levels of accuracy around 94 to 100%."

Dr Vendemia says her research has found it takes longer for the brain to process lies, than to process the truth and this, she says, can be tested by monitoring the brainwaves.

The new system relies on brainwaves

Her work is funded by US government grants but she says there were ethical questions which arose from it.

Could it be used, for example, to help in the interrogation of innocent people accused of being al-Qaeda terrorists?

"Anything can be misused. As a researcher working with technology which has huge implications you have a responsibility to make sure that what you are doing is ethical and make sure there is someone more objective than you looking at what you do," says Dr Vendemia.

Professor Paul Matthews, a neuroscientist at Oxford University, says a mind-reading machine is pure science fiction. "There is no technology which can tell somebody what you are thinking. But you can see what sort of areas of the brain are active. It is the same sort of technology which is used in hospitals with MRI and EEG scanners."

Tor Butler-Cole, a philosopher and ethicist from King's College, London, thinks we should be wary of allowing this technology to be used if it is not 100% accurate.

"The recent controversy with cot deaths has taught us that we should be aware of relying on science which may turn out to be wrong," she says.

Ms Butler-Cole believes there is also the danger jurors would give it a lot of credibility simply because it was "scientific evidence".

Dr Vendemia was one of a number of experts discussing the subject of "Criminal Memories" in a special debate at the Dana Centre in London on Thursday. The event will be shown on a webcast next week.