Kanner’s “refrigerator mother” hypothesis was disproven in the late 60s to early 70s due to apparent biological roots, thus shifting the DSM-3 in 1980 to categorize it as a developmental disorder that was not related to schizophrenia. The DSM-3 further defined three essential features for a diagnosis of autism: lack of interest in people, impairments in communication and bizarre responses to environmental stimuli, and all developing within the first 30 months of life. This was further revised in 1987, adding a mild diagnosis of pervasive developmental disorder-not otherwise specified (PDD-NOS) and dropping the requirement of onset before 30 months.