MTR journeys between Wan Chai and Causeway Bay have become more interesting in recent months, thanks to a technology based on a 19th-century English toy. The toy, known as the zoetrope, is the inspiration for a new advertising medium on subway tunnels marketed by SubmediaAsia. 'I always wondered, when people are sitting in a train with nothing to do, why someone didn't develop some technology to utilise tunnel wall space,' said Submedia co-founder and chief executive Douglas Woodring. An American astrophysics student adapted the humble toy for use in advertising that keeps pace with commuters sitting in moving trains. Slit panels cover images fixed to the walls of the subway tunnel. Passengers need to pass by the images at more than 4.8km/h for the slits to act as shutters in a movie projector, resulting in fluid motion pictures. Since the medium first appeared in the region at the beginning of the year, Submedia has provided moving advertisements for well-known brand names including Cathay Pacific Airways, United Airlines and Visa. 'Hong Kong was the first city in Asia where this new advertising medium was introduced,' Mr Woodring said. '[In early June] we introduced it in Japan on the Ginza railway line in Tokyo.' The system was first used in the American city of Atlanta in 2001 before being introduced on the New York subway system a year later. The cost of the new technique is comparable with other mediums, Mr Woodring said. 'Our clients to date have been pleasantly surprised. We know that [train operators] will be impressed with what we offer once they have seen it.' According to research conducted by AC Neilson, Hong Kong commuters have an advertisement recall rate of 75 per cent, which is in line with 85 per cent in the United States. Advertisers now acknowledge that the medium has endless possibilities, according to Mr Woodring. 'For instance, you could have a ballerina, singer, or actor promoting an upcoming performance,' he said. 'Or have dancers and circus performers providing a short preview of what an upcoming show will feature.' Mr Woodring recalls a Cadillac advertisement on a subway tunnel in the US. 'People were saying 'look how fast that car is moving', because it was moving alongside them, whereas it is the pace of the train that dictates the pace of the car, and this is a sensation not provided by TV and movies.'