The purpose of this study is to test how the brain responds when enjoyable foods such as chocolate are consumed. The investigators know that eating certain types of foods can make an individual want to keep eating even when he or she is full. The chemical in the brain that causes this is called dopamine. The investigators can measure this response by looking at changes to how an individual's eye responds to light.

The overall objective of this study is to determine dopamine (DA) neuromodulation (changes in b-wave amplitude as measured by electroretinography (ERG)) in response to consuming a highly reinforcing food (chocolate). The investigators hypothesize that orosensory stimulation with chocolates with increasing sugar content will increase the beta wave (b-wave) amplitude and the increase in the b-wave amplitude will correlate with score changes on the Psychophysical Effects Questionnaire (PEQ). This will be accomplished by testing different chocolates (extreme dark (90% cocoa), dark (70% cocoa), milk (38% cocoa), and white (0% cocoa)) on different days using 1.0 cd∙s/m2 flash luminance energy.

Inclusion Criteria:

• BMI 20-24.9 kg/m2
• ability to understand and sign the consent form
• availability of transportation (i.e., participants must be able to provide their own transportation to the Grand Forks Human Nutrition Research Center)
• be free of any major illness/disease

Exclusion Criteria:

• food allergies
• participation in a weight loss diet/exercise program
• pregnancy
• lactation
• metabolic illness/disease (diabetes, renal failure, thyroid illness, hypertension)
• eye illness/disease (narrow angle glaucoma, macular degeneration, retinal detachment, cataracts)
• psychiatric, neurological or eating disorders (schizophrenia, depression, Parkinson's Disease, Huntington's Disease, cerebral palsy, stroke, epilepsy, anorexia nervosa or bulimia nervosa)
• taking any type of prescription medication with the exception of oral contraceptives and antihyperlipidemia agents

Community sample