Mixed cells in the cat lateral geniculate nucleus: functional convergence or error in development?

In the A laminae of the cat dorsal lateral geniculate nucleus, most relay cells can be unambiguously classified as X or Y. A small fraction, however, are reliably found to have mixed properties arising most likely from convergence of retinal X- and Y-cell axons onto single relay cells. It is suggested that this convergence is not functional, but rather is an error in development.