Learning disabilities, conditions or factors that hinder one's comprehension or impairs one's ability to use standard educational tools and methods. An inability to perform in the school environment at the same level as one's peers can be the result of an inherited condition causing mental retardation, a developmental defect, a physical handicap such as impaired hearing or vision or muscle incoordination, an allergy causing hyperactivity, or even a reaction to medications taken to control hyperactivity. Learning problems are first identified through tests that measure reading, writing, and arithmetic performance correlated to age, experience, and family background. One common learning disability is dyslexia, the mental reversing of printed letters and inability thus to comprehend the meaning of written text. Its cause can lie in the brain, the eyes, or another part of the body. Writing disabilities frequently come from a lack of coordination between the brain and the muscles. A mathematics disability seems to reflect problems of memory and can exist with or without a reading problem.