How did Haldan Keffer Hartline study receptive fields in vertebrate eyes?

In 1938, American physiologist Haldan Keffer Hartline pioneered the study of receptive fields by becoming the first scientist to isolate and record electrical responses from single optic nerve fibres in vertebrate eyes.1

To conduct this research, Hartline utilized microelectrodes to measure the electrical activity of individual nerve fibres. He defined the receptive field of a retinal ganglion cell as the specific area of the retina from which an increase in the frequency of action potentials could be elicited by light stimulation.231

By stimulating these retinal areas, Hartline demonstrated that the visual system does not merely transmit raw light intensity but integrates visual information through the activity of these individual units. His work established the foundational concept of the receptive field, which was later expanded by other researchers to include the complex excitatory and inhibitory interactions—such as centre-surround antagonism—that allow the eye to enhance contrast and perceive shapes.213