Dot-probe task with nicotine images, the following project includes two type of nicotine stimuli: primary stimuli and secondary stimuli, each one containing a total of 12 pair of images repeated 4 times in a random way (48 trials per stimuli type). Between the primary and secondary stimuli there is a 2 minutes pause to let the subject recover its attention. There is a random loop to allow the primary and secondary stimuli to always be selected in a different random order