The degree of sense impairment may differ greatly from one person to another. One may be totally deaf, having no residual hearing, while another may find it difficult to hear under certain circumstances, perhaps when there is much background noise. Actually, most deaf people can hear some sound, even though they cannot hear speech.

For example, technicians use equipment to establish the level of hearing. Then doctors try to determine the type of impairment. Is the problem due to faulty transmission of the electrical impulses to the brain? Is the impairment correctable with surgery?