Intermittent Visual Perturbations to Enhance Balance Training

Inclusion Criteria: * Ages 18-30 years, or 65-89 years. * Ability to walk independently for 10 minutes continuously. * Willingness to be randomized to any experimental group and to participate in all aspects of study assessment and intervention Exclusion Criteria: -Major cognitive disorder that interferes with independence, based on affirmative response (always/usually/sometimes) to the following question: "As a result of confusion or memory loss, how often do you need assistance with day-to-day activities such as cooking, cleaning, taking medications, driving, or paying bills? Would you say it is 1) Always; 2) Usually; 3) Sometimes; 4) Rarely; or 5) Never". * Current or recent (within 6 months) lower limb musculoskeletal injury that causes pain during walking or limits walking ability. * History of neurological injury or disability (including spinal cord injury, stroke, Parkinson's disease, or multiple sclerosis). * Difficulty communicating with study personnel. * Current enrollment in any other clinical trial. * Low vision that cannot be corrected by wearing contact lens. Low vision will be operationally defined as visual acuity less than 20/70 on standard eye chart, or difficulty perform complex walking tasks due to visual conditions affecting accurate navigation around and over obstacles (self-reported or observed by examiner). The goggles to be used in the study do not permit eyeglasses while using them. * Illiterate or non-English speaking, due to the likelihood of difficulties following protocol instructions.