Vernier acuity as a test of magnocellular sensitivity

Vernier acuity has been argued to provide a means to measure the integrity of the magnocellular visual pathway. This proposal is reviewed here and found to be inadequately supported for the following reasons: (1) the conditions under which Vernier acuity corresponds to magnocellular resolution differ from those used in psychophysical tests; (2) Vernier offsets can be induced by adaptation of cortical neurons; (3) factors other than the magnocellular system have the ability to interfere with Vernier acuity. Taken together, this review argues that Vernier acuity is at best limited as a selective test of magnocellular sensitivity.