Midget cells originate in the ganglion cell layer of the retina, and project to the parvocellular layers of the lateral geniculate nucleus (LGN).
In many cases, they are connected to midget bipolar cells, which are linked to one cone each.
[1] These neurons show roughly circular receptive fields with antagonistic center and surround; this property is known as spatial opponency and these neurons are typically divided into ON- or OFF-center, depending on whether they are excited or inhibited by photons falling on the center of their receptive fields.
[2] Most of these cells are chromatically opponent, meaning that long- and medium-wavelength visible light (commonly approximated to red and green, respectively) exert opposing effects on the center and the surround.
[2] For instance, a chromatically opponent L-ON (Long ON) midget cell would be excited (and more likely to spike action potentials) if light of long wavelength falls on the cone or cones in the center of its receptive field but would be inhibited by medium-wavelength light falling on the surround of its receptive field.