**Study Overview:** This research explores how taste works in three groups of people: healthy individuals, those with early Parkinson's disease (a brain disorder causing movement problems), and those with Lewy body disease (another brain disorder affecting memory and thinking). The study uses a method called gustatory evoked potential analysis to understand how these groups process taste differently. The results might help us learn if taste signals are processed differently in the brain depending on the disease. **Eligibility:** To join, participants must be adults who have given written consent and must fast (not eat) for over 2 hours before certain tests. Body Mass Index (BMI), a measure of body fat, should be less than 30. Participants should not have serious cognitive issues or be taking medicines that affect taste. Pregnant or breastfeeding women, or those with certain health conditions, cannot participate. **Key Points:** - **Length/Visits:** Participation involves fasting before tests; the exact duration of the study is not specified. - **Compensation:** No information about compensation is provided. - **Risks:** Participants should consider any health conditions or medications that might interfere with taste tests. Study participation requires careful consideration of eligibility and health conditions.