Will computer-created human beings in film or video games ever achieve complete believability, or will a discerning public always be too unnerved by the results?

This is the focus of work by researcher Angela Tinwell, who is looking at the concept of the "uncanny valley" - a phrase that describes the negative reaction people experience when computer-generated imagery of humans is "too realistic".

In short, you can make a hedgehog run around on its hind legs fighting evil, and people will find it adorable. But if you animate a life-like human, the brain starts to single out the inaccuracies and focus on them. And it causes unease.

"I'm fascinated by the increase in realism that is creeping into video games," said Dr Tinwell, a senior researcher in games and creative technology at the University of Bolton.

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"You find there's a feeling of being uncomfortable when computer-generated characters are too real. With non-human characters with human-like traits, such as Sonic (the Hedgehog), it's different. But people are less accepting of characters as their human likeness increases."

Despite lots of people giving their views on the uncanny valley, little had been done to substantiate them. "There is no real empirical evidence to show designers why there is this negative response," Dr Tinwell says, explaining the reasons behind her research.

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The phenomenon was originally described by Japanese roboticist Masahiro Mori. The "uncanny" refers to our emotional response to a robot or character, while the "valley" comes from a graph Mori created to demonstrate the phenomenon. It plots the dip in the positivity of human reaction to the realism of a character, and this dip is the valley.

Although people generally tend to warm to anthropomorphic creatures, when an animated character becomes too humanoid our perceptions can change very quickly.

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"Take the characters in [the film] Avatar," Dr Tinwell observed. "They are not strictly human because they have blue skin. I think [director James] Cameron introduced this feature as it reduces expectations. Because of the blue skin, we were more forgiving, since the film is not trying to convince us that they are human. However, when Steven Spielberg presented Tintin he was ripped apart, and criticised for creating an uncanny character."

According to Dr Tinwell, any inaccuracies in visual facial markers - however small - can increase the creepiness of animated human characters.

"I conducted a study, which is currently under review, about the possible perception of psychopathic tendencies - particularly related to a lack of non-verbal communication movement and expression in the upper face," she said.

The study found that even a relatively small lapse in realism, such as the lack of an eyelid or eyebrow movement, could lead study participants to suspect the character was harbouring "aggressive tendencies".

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The findings could have knock-on effects in the real world, Dr Tinwell noted, specifically for the cosmetics industry, where treatments that use botulinum toxin (also known as Botox) have a restrictive effect on facial expressions.

"This has potential implications for cosmetic procedures that include Botox, which reduces facial movements," she says, raising the possibility that human beings could "fall into the uncanny valley".

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Dr Tinwell believes that animators and designers will struggle to perfect the most nuanced subtleties of human appearance - such as smiling and eye contact - despite ongoing improvements in technology.

As computer-generated imagery techniques develop, so does our sensitivity to what is real and what is not real. We become more attuned to how computer-created pictures differ from reality. Considering this process has led Dr Tinwell to propose the concept of an "uncanny wall", which will never be overcome.

"Overcoming the uncanny valley may be an impossible feat," she said. "I predict that the viewer's discernment for detecting imperfections will keep pace with technological developments. We will always stay one step ahead."

If that is the case, why do designers continue to develop more and more realistic computer games characters, particularly if the end result often leaves viewers feeling uneasy?

"There is a bit of a paradox here, in that developers are continuing this pursuit of realism, and trying to test the threshold of acceptance, knowing that people will not necessarily see the results as an advantageous thing," Dr Tinwell acknowledged.

"But I think it's addictive. The designers want to be the first to overcome the uncanny valley. It's a bit like the race to the Moon."

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chris.parr@tsleducation.com.