This study is being done to better understand how vestibular problems and thinking abilities (such as attention and mental flexibility) are related in older adults, and how doing a balance task and a thinking task at the same time affects their performance. Older adults will first complete questionnaires and simple paper-and-pencil tests of attention, memory, and mental rotation while seated. They will then perform standing balance tasks on a portable force platform under different conditions (eyes open, eyes closed, standing on a foam surface) and will repeat some of the thinking tasks at the same time. Next, participants will walk on a treadmill while wearing small motion sensors, both with and without added thinking tasks such as serial subtraction and digit reordering. The total testing time is about 90 minutes. Two groups will be included: healthy older adults and older adults who have had dizziness or falls in the past two years. By comparing these groups, the study aims to provide a basis for designing future dual-task assessment and training programs to reduce balance problems and falls in older adults.