Is coherent motion an appropriate test for magnocellular sensitivity?

The suggestion that coherent motion may serve as a test of magnocellular sensitivity is problematic. However, the nature of the problems depends on how the "magnocellular system" is defined. If this term is limited to subcortical entities, the problems are that subcortical neurons are not directionally selective, and that their receptive fields are too small to account for the spatial summation of coherent motion. If "magnocellular system" is defined to include cortical entities, such as area MT, one is faced with the fact that this definition itself is problematic as well as the problem that area MT is known to receive parvocellular and koniocellular inputs.