A letter to Henry Cline, Esq. on imperfect developements (sic) of the faculties mental and moral, as well as constitutional and organic; and on on the treatment of impediments of speech. London: Arch, Cornhill; Ridgeway, Piccadilly, 1810.
The first book on mental deficiency. Thelwall recognized that sensory deprivation could be a cause of apparent mental defect through his work with handicapped children. He established criteria for distinguishing between intellectual capability and performance. Digital facsimile from the Internet Archive at this link.
Subjects: NEUROLOGY › Neurodevelopmental Disorders › Mental Retardation, PSYCHOLOGY, Speech, Anatomy and Physiology of