Smallest channel in early human vision.

We suggest from the psychophysical data on two-point and line acuity that the smallest foveal channel in human vision must have an excitatory center with a diameter of around 1' 20". Taking into account the optics of the eye and the finite size of the receptors, we show that this would correspond well to the properties of a retinal ganglion cell receiving excitatory input from a single cone.