There was one capital English letter set (A-Z) for each position. Each letter was presented once in each position. There were 26 trials for each treatment. For the first trial, the computer randomly selected one capital English letter from the letter set for each of positions 1, 2, 3 and 4, respectively. Then the presented letters were deleted from the letter set for that position and recorded in a file. In the second trial, the computer again randomly selected one letter from the remaining letter sets for positions 1, 2, 3 and 4 again. The procedure was repeated iteratively until the letter sets were empty.