Naming difficulties may be rank ordered along a continuum. Items are rank ordered in terms of their ability to be named, which is correlated with their frequency. This type of picture-naming test is also useful in the examination of children with learning disabilities and the evaluation of brain-injured adults.
The Jarvik-7 heart was developed by American scientist Robert Jarvik and his mentor, Willem Kolff. In 1982, Seattle dentist Dr. Barney Clark was the first person implanted with the Jarvik-7, the first artificial heart intended to last a lifetime.
Andrew Huxley and Alan Hodgkin, in 1952, discovered the ionic mechanism in which nerve impulses are transmitted. As a result of advances in the physiological studies of the heart, Christiaan Barnard, South Africa, performed the first successful human heart transplant in 1967.