Additional Study Information: This project aims to develop electroretinogram as a new putative marker for dopamine release, and as a predictor of treatment response among patients seeking treatment for smoking cessation. Tobacco smoking continues to be a major public health challenge. Dopamine is a neurotransmitter released in the brain. Several lines of evidence suggest that dopamine release deficit in the brain is involved in the development and maintenance of nicotine dependence. The investigators hypothesize that smokers who do not have a deficit in dopamine release will more readily respond to behavioral treatment for smoking cessation, and in particular, financial incentives contingent on abstinence (Contingency Management). Previous pilot data suggest electroretinogram (ERG), which records electrical signals from the retina in response to light, is a clinically accessible correlate to dopamine release in the brain. The project proposes an ERG-based biomarker, and a pilot clinical trial to apply this biomarker to personalize smoking cessation treatment. This clinically tractable biomarker of central dopamine release may have a large number of future applications in the diagnosis and treatment of other mental illnesses and substance use disorders.The study will recruit normal controls and smokers, measure ERG before and after a standard dose of oral immediate release methylphenidate. Smokers will undergo a 12-week standardized treatment course of CM. The investigators will test whether smoking status and the response to CM are correlated to changes in ERG in response to methylphenidate challenge.