Dr Rabindra Mehta, who is also a sports aerodynamics consultant, says that England's fast bowlers in India have made the ball swing towards the smooth side after learning the new technique from former England and now Australia bowling coach Troy Cooley.
''Whenever an old ball swings, commentators label it reverse swing. Often though, it is not true reverse swing they are observing, but what I call 'contrast' swing,'' writes Dr Mehta, who has spent 25 years studying how a cricket ball swings, in the April issue of The Wisden Cricketer.
''For conventional swing (away), the ball is released with the seam angled towards first slip or fine leg, spinning backwards along the seam and with the polished, smooth side facing the batsman. The ball will then swing in the same direction as the seam is pointing.''
''For true reverse swing the ball is released in the exact same way, except with the rough side facing the batsman. In this case, the ball will swing in the opposite direction to that of the seam.
But, if a sharp contrast in surface roughness is generated on the ball, so that one side is smooth and the other rough, the ball can be made to 'contrast' swing with the seam positioned vertically (pointing straight down the pitch).'' Dr Mehta, who studied at Worcester Royal Grammar School in the 1970s with an emerging Imran Khan, says that with contrast swing the ball will generally swing towards the rough side at lower bowling speeds (less than 70 mph) and towards the smooth side at higher speeds.
He says the main advantages of the new technique are that it is easier to produce, the ball can be swung both ways and the ball will swing even if the seam is completely flattened. On hard pitches, such as those on the subcontinent, the rough surface and flat seam come easily, so the key to successful contrast swing is to keep one side as smooth as possible with vigorous polishing.
Dr Mehta also provides how to identify ''contrast'' swing.
''When the ball swings, make note of the seam position and swing direction. If they are the same, it is conventional swing; if opposed, it is reverse swing; and, if the seam is pointing straight down the pitch, it is contrast swing,'' he wrote.