The Interchangeable Music Puzzle/Switch, model 921, is a puzzle switch, adapted music box, eye hand coordination activity, and spatial orientation activity, designed for use by children and adults with brain injury or cognitive disabilities. This puzzle has removable blocks which allow the user to progressively increase the skill required to complete the task. Start with one shape and any four blank blocks and build up to five distinct shapes. When the task is completed, music plays. If a reward toy or device is connected to the blocks, it automatically turns on without music. Blocks can be shifted or rotated to teach spatial relations, form constancy, and mental imagery. OPTION: Set of replacement blocks (model 921-K). POWER: Uses 1 double-A battery. DIMENSIONS (HxLxW): 1.25 x 4.75 x 15.5 inches.