Study participants will be recruited in two age groups: young (18-28 years) and old (60-85). Each participant will participate in two psychophysical and electrophysiological test sessions. For each of the two sessions, the participant will be administered gum before the test. For one of these sessions, the gum will be polacrilex that contains 6-mg nicotine, and for the other session, the gum will be a placebo control. The study will be double-blind, meaning that neither the experimenter nor the participant will know whether the participant has received nicotine or placebo for a given session. The study has a cross-over design, meaning that all participants will receive both nicotine and placebo in separate sessions. Finally, the order of drug administration will be counterbalanced, meaning that equal numbers of participants will receive 1) nicotine in session one and placebo in session two, and 2) placebo in session one and nicotine in session two.
