I was watching an old repeat of Cops tonight on TV and saw a police officer performing tests on a man suspected of being on illegal narcotics. The dude was on meth and was scrutinized by the officer by matching his pupil size to a chart and testing the reaction of his pupils to light. However the cop mentioned a test they perform to find out whether someone is under the influence of marijuana (the suspect claimed he was just stoned, not on meth). The test involves pointing a finger straight at the suspected marijuana smokers' eyes in which he's expected to follow the finger with his vision, coming closer until the finger touches the patch between the eyes. The officer claimed that if the pupils do not cross over, as they normally would, as the finger comes in closer, that the suspect is under the influence of marijuana. This seemed odd to me. Could this possibly be true?