'''Haldan Keffer Hartline''' (December_22, 1903 – March_17, 1983) was an American physiologist who was a cowinner (with George_Wald and Ragnar_Granit) of the 1967 Nobel_Prize_in_Physiology_or_Medicine for his work in analyzing the neurophysiological mechanisms of vision.
Hartline began his study of retinal electrophysiology as a National Research Council Fellow at Johns_Hopkins_University, Baltimore, receiving his M.D. in 1927. After attending the universities of Leipzig and Munich as an Eldridge Johnson traveling research scholar, he became professor of Biophysics and chairman of the department at Johns Hopkins in 1949. One of Hartline's graduate students at Johns Hopkins, Paul_Greengard, later also won the Nobel Prize. Hartline joined the staff of Rockefeller_University, New_York_City, in 1953 as professor of neurophysiology.
Hartline investigated the electrical responses of the Retinas of certain Arthropods, Vertebrates, and Mollusks because their Visual_systems are much simpler than those of humans and are thus easier to study. He concentrated his studies on the eye of the Horseshoe_crab (Limulus polyphemus). Using minute electrodes in his experiments, he obtained the first record of the electrical impulses sent by a single Optic_nerve fibre when the receptors connected to it are stimulated by light. He found that the Photoreceptor_cells in the eye are interconnected in such a way that when one is stimulated, others nearby are depressed, thus enhancing the contrast in light patterns and sharpening the perception of shapes. Hartline thus built up a detailed understanding of the workings of individual photoreceptors and nerve fibres in the retina, and he showed how simple retinal mechanisms constitute vital steps in the integration of visual information.
==External links==
*Nobel biography
Hartline, Haldan Keffer
Hartline, Haldan Keffer
Hartline, Haldan Keffer
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