But the worlds of Total Recall, Star Trek and eXistenZ are not as far away as their creators may have thought.

An extraordinary experiment by scientists in California interpreted, using "linear decoding technology", a cat's brainwaves from a point just behind its optic nerve and translated them into images.

The hazy, but recognisable black and white pictures could be made out as faces and woodland scenes. The researchers had managed to "see" through the eyes of a cat.

The implications of the experiment - in areas including medicine, civil engineering, warfare and computer development - are wide ranging. In medical terms, "seeing" through a patient's eyes would give doctors clues about their health.

If the vision were blurred, or impaired in some way, the cause might be a stroke - or if colour vision is affected, the cause might be colour blindness or diabetes.

Prosthetic limbs

On a more sci-fi tack, any advance in "interfacing" hardware with organic brain matter represents, among many other things, a step towards a day when prosthetic limbs - or any type of machinery - may be thought-activated.

Because the research carried out on the cat focused on an area of the brain fairly close to the eye, it concerned "raw" data. If - to pose the question that this experiment inevitably raises - the wires had been inserted into a human being's brain, the images gained would not have effectively been thought processed.

In Total Recall, Arnie's memories were tampered with

So it would not be possible to "see", for example, hallucinations, had the cat been psychotic or taking drugs. Removing the sticky subject of ethics from the equation, the technology also opens the door for animals to be used and trained in a whole range of situations where robots are currently employed.

Theoretically, by fitting a transmitter onto the headset wiring of the cat, it would be possible to send it down a blocked pipe, for example, so that it could beam up pictures of where the trouble was.

The local council could save thousands of pounds in digging up an entire street, thanks to the remote vision of their feline worker. Similarly, birds could be trained to act as real spies in the sky, and dolphins could check out the enemy's submarines.

Which is where it all gets a bit Big Brother. Another possible application of the cat experiment is that people fitted with linear decoding equipment could act as spies - or conversely, have their every movement surveyed from within.

Realtime video

Futurist Ian Pearson predicts that soldiers, somewhere in the not too distant future, would have a CamNet headset fitted to their helmets to provide HQ with realtime video information.

He writes on his website that some soldiers would look like the Borg in Star Trek, and that their instructions would come from perhaps thousands of miles away, and that even their weapons might be able to be remotely fired or disarmed.

eXistenZ players plugged their computer games into their own central nervous systems

He writes: "Of course, the soldiers will have computers to provide battlefield information, recognise and enhance images and provide instructions in front of the soldier's eyes via an eyepiece.

"With video cameras in smart weapons relaying images to the eyepiece, the soldier can watch what is going on, aim and fire the weapon with greatly reduced personal exposure.

"Of course, this will use the latest night vision technology and be sensitive to a much greater range of the spectrum than the Mk1 human eyeball. Eventually active contact lenses will give soldiers 3-D overlays of information on the real world, enhancing their effective vision and highlighting targets or threats."

But what if instead of external apparatus to achieve these objectives, the soldier's brain was wired up to relay the information back to base? Writing about the possibility of a holodeck ever making an appearance, Mr Pearson says that perhaps by 2015 and certainly by 2020, inputs should be able to be made directly into the peripheral nervous system - creating virtual sensation.

His website continues: "The very long-term future involves direct brain links - real Total Recall stuff, expected some time after 2030. This could in principle be completely indistinguishable from reality."

Sentient creatures

So if you could see through the eyes of another person, and simulate the sensations that they might be feeling, it might even be possible to virtually step into another person's shoes.

Mr Pearson says that predicting the technological future always involves looking at what the social and economic climate of the time might be as well. The most applicable advances likely to come out of this experiment, according to biomechanical scientists, might be a furtherance in the understanding of the thought process.

Futurist Ian Pearson says real Total Recall stuff is expected around 2030

Currently, computers "think" far more quickly than human beings, but they do it sequentially. Sentient creatures, on the other hand, manage to handle several layers of thought in parallel.

The cat in the experiment experienced a mixture of shapes, definitions, vertical and horizontal lines, and formed them into a picture. It was also breathing and maybe feeling hungry or sleepy - or wondering what the blazes was sticking out of its head.

Knowing how that parallel thinking happens will edge scientists towards developing computers that can contemplate more than one thing at a time. And, say the scientists, the day that parallel computing is achieved will mark the real leap into the world of science fiction.