The responses of single optic nerve fibers of the vertebrate eye to illumination of the retina.

Hartline continued and extended the work initiated by Adrian and Matthews on electrical discharges from the optic nerve. See also his later papers In the same journal, 1940, 130, 690-711. Reprinted with historical introduction by Hartline in F. Ratliff (ed.). Studies on excitation and inhibition in the retina, New York, [1974].

In 1967 Hartline shared the Nobel Prize in Physiology or Medicine with Granit (No. 1534) and G. Wald (No. 1535) "for his discovery of the optical nerve network."