Development of X- and Y-cells in kittens.

A contrast reversal stimulus was used to classify the retinal ganglion cells of kittens 3--12 weeks of age. At 3 and 4 weeks of age, the majority of the units were classified as Y-cells. The percentage of X-cells was similar to that of the adult at 5--6 weeks of age although other response properties were not adult-like. The angular size of the receptive field center was significantly larger than that of the adult through 5--6 weeks of age. An estimate of the position of the vertical meridian was obtained from the positions of the receptive fields in the visual field which permitted the calculation of the posterior nodal distance in kittens of various ages. From the posterior nodal distance, the linear extent of the receptive field center was determined. This showed that there is only a very slight increase in the linear size of the receptive field center from 3 weeks to adulthood.