As the woman in this VR-enhanced scene holds her straw out to Wu, enticing him to drink with her and the man, Wu remains captivated for at least 10 seconds – a detail the observers note with interest.

Although he can choose the scenes to view and their duration by using the switch he holds in his right hand, “Wu’s attention is stuck on this scene for a while before [he moves on] to look at other no-drug scenes”, an officer told the South China Morning Post.

“It means he is still a bit interested in having drugs.”

It is all part of a revolutionary effort to use VR technology to reveal the extent of drug users’ addiction – and the type of treatment they need – to help them to turn their lives around.

Clad in the centre’s official inmate uniform of green sleeveless T-shirt, shorts and sandals, Wu and his fellow addicts are part of a trial of VR technology that was expanded this summer to all five of Shanghai’s rehab facilities, from just two in October.

Although the Shanghai centres were not the first in China to begin using VR – some rehab institutes in the eastern province of Zhejiang had employed it last year – their application of the technology is nevertheless distinctive in its application of eyeball movement tracking science.

Being able to read how an inmate’s eyeballs move over certain images gives staff a clearer idea of whether the addict’s gaze is fixed squarely on the repulsive “educational” images of drug addicts he or she must watch.

Tracking eyeball movement also gives staff extra information they can use to gauge the accuracy of the self-evaluations that inmates are required to fill out; many have been known to lie about the degree of their drug dependency in an attempt to speed up their release from the programme.

“In the rehab centre we see those awful pictures of drug addicts through VR helmet several times a month, as part of our education here,” Wu told the Post. “I really abhor drugs now.”

While it is not known how many addicts in China ultimately are to be exposed to the VR programme, the number is expected to be considerable. The five centres in Shanghai and one at Qingdong alone treat 1,800 male addicts.

Xu Ding, a drug rehab veteran from Shanghai Drug Rehabilitation Management Bureau who spearheads the VR project, said the technology’s use has helped alleviate “a major frustration” encountered when trying to treat drug addicts by showing them revolting images of other addicts.

“In the past, to depress the addicts’ desire for drugs, we let them watch TV or presented them horrible pictures of people whose health was seriously affected after long-term consumption of drugs,” Xu said. “But both TV or pictures on papers don’t look real enough.

“What’s more, we can’t tell if these people are really focusing on our education,” Xu said. “They would look at other places, or just close their eyes.”

In 2015, when the VR industry was beginning to get a lot of attention in China, Xu and his colleagues moved to incorporate it in treating addicts. “VR is a kind of embedded viewing experience and is so real,” Xu said.

The VR system that was first used in two of the city’s rehab centres in October was jointly developed by Shanghai Mental Health Centre, East China Normal University’s School of Psychology and Cognitive Science, eyeball movement tracking company Shanghai Qing Tech and the Shanghai drug rehabilitation authority.

In the system, an instrument to trace eyeball movement is installed in the VR headset along with devices to measure electrodermal activity (EDA) and pulse phase, to make observers aware when addicts refuse to look at what they are supposed to see.

EDA measures the change in the electrical characteristics of a person’s skin in response to sweat secretion.

“Shanghai is the first in the world to introduce an eyeball-movement tracking machine to drug rehabilitation, according to the literature I can find on the internet,” Xu said.

Cao Lei, director of the psychotherapeutic department of Shanghai Qingdong Drug Rehab Centre, said the reports on addiction level based on inmates’ responses to watching VR scenes “are objective and people can’t fool the system since they can’t control their EDA and pulse speed”.

Previously, inmates could lie when filling out a questionnaire on their drug dependency to get released early, Cao said.

Under mainland law, people caught possessing drugs must spend two years undergoing treatment at a rehab centre. Inmates who “perform very well” in treatment can get out early.

So far, assessing the VR programme’s effectiveness is difficult, given the lack of concrete results.

Last year, however, the Ministry of Justice said many rehab centres across the country were using innovative methods to try to help people kick drug habits, including virtual reality technology, people.com.cn reported.

The measures, which also included Tibetan medicine, traditional Chinese medicine, massage and physical exercise, had achieved good results, according to the ministry.

Some 2.55 million people in China had possessed illegal drugs as of the end of last year, according to the 2017 China Drug Situation Report issued in June by the China National Narcotics Control Commission.

Among them, 321,000 were put in rehab centres across the country, about 2 per cent more than in the previous year. More than 60 per cent of addicts possessed synthetic drugs such as methamphetamine, a central nervous system stimulant known in the illicit drug trade as “ice”.

Wu, 28, said his drug habit began six years ago at a pub where a friend offered him ketamine – a synthetic drug that induces a trancelike state and is usually referred to on the street as “K powder”.

“I knew drugs are bad, but at that time I was confident that I could control myself [and would] not become addicted to drugs,” said Wu, a former sales representative with an insurance company.

But he failed to do that. Last year, police, tipped off by his friend that Wu had illegal drugs at home, raided Wu’s house and took him away.

“I think I will not touch drugs after I get out [of the rehab centre],” Wu said. “I don’t want to come back again. I hate losing my freedom.”