Definition
A formal stimulus class refers to a group of stimuli that share common physical characteristics, such as shape, color, size, or texture. Stimuli within the same formal class are categorized based on their physical features rather than their function or when they occur. This classification helps behavior analysts identify and group stimuli that may influence behavior in similar ways due to their shared attributes.
Example
A teacher presents a variety of objects to a child, including a red ball, a red apple, and a red car. All of these objects belong to the same formal stimulus class because they share the common physical feature of being red, even though they differ in shape, function, and purpose.