Language deprivation is associated with the lack of linguistic stimuli that are necessary for the language acquisition processes in an individual, usually in a very impoverished environment. Experiments involving language deprivation are very scarce due to the ethical controversy associated with it. Roger Shattuck, an American writer, called language-deprivation research "The Forbidden Experiment" because it required the deprivation of a normal human. Similarly, experiments were performed by depriving animals of social stimuli to examine psychosis. Although there has been no formal experimentation on this topic there are several cases of language deprivation. The combined research on these cases has furthered the research in the critical period hypothesis in language acquisition.
The most well-documented case of a language-deprived child was that of Genie. Genie was discovered in 1971 in the family home, where she recognized as highly abnormal. A social welfare agency took her into custody and admitted Genie into a hospital. Before discovery, Genie had lived strapped and harnessed into a chair. Genie, 13 years of age upon discovery, was malnourished, insensitive to tactile senses, and silent even upon being evoked; however she had proper social skills and she was able to maintain eye contact with caregivers, giving the impression that she understood instruction. After being discharged from the hospital she was put in foster care where she received "informal" training.
The first tests of language were taken three years after her discovery. She was given a variety of language test measures to test her sound skills, comprehension skills, and grammatical skills. She was able to discriminate between initial and final consonants. However, she lacked pitch and volume control, her speech was described as high pitched and breathy with sound distortions, consonant clusters, neutralizing vowels, dropping final consonants, and reducing consonants. She was able to comprehend instructions but was dependent on pantomime and gesture. Genie was capable of discriminating affirmation from negative, comparative adjectives, and colour words. After four years of language stimulation, her linguistic performance was similar to that of a normal 2-year-old infant. She had poor performance in complex sentences, interchangeably used the pronouns "you" and "me", and lacked the question form of sentence structure. Further studies were conducted focusing on the physiological state of Genie. She was right-handed but neurological tests showed that she processed her language in the right hemisphere. Normally right-handed people process language in the left hemisphere. She excelled in right-hemisphere processed tasks, such as face perception, holistic recall of unrelated objects, and number perception. Genie's language skills were deemed as poor, and this was linked to the notion that she began to learn language when she was 13 ½.
Another case of language deprivation was of Kaspar Hauser, who was kept in a dungeon in Germany until the age of 17. He did have some contact with humans during his isolation. Sources stated that he had a small amount of language; other sources state that upon discovery he spoke a garbled sentence. He was able to learn enough language to attempt to write an autobiography and to also become a legal clerk. However, five years after discovery he was stabbed to death.
Anna was born March 6, 1932 and was an illegitimate child. She was put in isolation by her mother because of this. Anna was kept tied to a chair and was malnourished due to being fed milk only. Upon discovery on February 6, 1938, she was sent to a county home. Further examination of Anna determined that she was very poor physiologically but that her senses were intact. During her stay at the county, she regained some body weight and began to build muscle in her body. She lived at the county home for 9 months until she was moved to a foster home. Upon leaving she was still very unsocial, because there was no predetermined caregiver in the county home, which consisted of over 300 inmates and one nurse; often she was taken care of by inmates. The caregiver at the foster home used the same method to talk to Anna by which a mother would talk to their infant. During her tenure at the foster home she became more human, and was similar to a one-year-old. After a year at the foster home she was sent to a school for defective children. Although she could not speak at the time, she had a comprehension of instructions.
Another case of a child deprived at a young age is that of Isabelle. Confined to a room with a deaf and mute mother, she spent 6 ½ years in silence without any language stimulation. Upon discovery she was sent to a hospital where she was monitored for her apathetic behaviour. Now in a ward with children, she began to imitate other children in the ward to request attention. She had also begun language training. Eighteen months into her training her repertoire of words was estimated to be 1500–2500 words; she was also able to produce complex sentence structures. Throughout her training she began to use correct inflectional morphology, pronouns, and prepositions.
Feral children are children discovered by society to be living in the wild with the assumption that they were raised by animals. It is stated that such children are deprived of human associations and are too strongly conditioned with animal behaviours, such that the human development are permanently inhibited and the animal inhibitions are never lost throughout life. There are several known cases of feral children relearning language, the most well-known is Victor. Victor was found at the age of 13 and was given to Dr. Itard, who "experimented" on the child. Victor was also known as the "wild boy of Aveyron". He was characterized to be insensitive to temperature, uncivilized and to run on all fours. Dr. Itard conducted training over a period of 5 years, during which time Victor was able to recover some speech.
The "critical period of learning" hypothesis states that for a must be exposed the language by a certain age to acquire language. It is said to be associated with a period of increased neuroplasticity. It is also thought to end around the onset of puberty.
Language Deprivation in Deaf and Hard of Hearing children similarly occurs when sufficient language exposure does not occur within the first few years, or critical period of development. This is common with Deaf and Hard of Hearing children as they cannot access the world around them to some degree through auditory means as their hearing counterparts do. These children often arrive to school, whether preschool or kindergarten age, with significant language delays that can greatly impact the rest of their educational career. Accommodations and specialized methods of instruction are required to meet their unique needs.