Visual cortex cells respond to orientation
In October 1959 David Hubel and Torsten Wiesel described the fields of single cells in the cat's primary visual cortex: each field split into excitatory and inhibitory regions lying side by side, and a cell was driven only by a stimulus of a particular shape, size, position and orientation.
Why it matters
It was the first showing that a cortical cell answers not to a spot of light, as a retinal cell does, but to an oriented stimulus. The model of vision as a hierarchy of features starts here, and artificial networks for pattern recognition later leaned on it.
Single-cell recordings in 24 lightly anaesthetised cats, the retinas stimulated with spots of light of various sizes and shapes. Of the 45 units studied, 36 were driven from one eye (15 ipsilateral, 21 contralateral) and 9 from both independently. Fields were oriented vertically, horizontally or obliquely; diffuse light over the whole retina was weak, because the excitatory and inhibitory regions cancelled. The full text was read in a copy of the scan on a third-party education server; PMC and the publisher's site are behind checks that were not worked around. The record does not use the language of slits of light: that is the 1962 paper's.