A device that allows someone to hear their own voice or sounds they produce, used for self-monitoring in speech or hearing tests.
From Greek 'auto-' (self), 'phone' (sound), and 'scope' (to view/examine). This scientific instrument emerged in late 19th-century speech pathology and audiology.
This is essentially an ancestor of modern voice-recording technology—speech therapists used it to let patients hear exactly what their speech problems sounded like, which was incredibly powerful for learning!
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