Sequential double training in Vernier discrimination. A, Schematic drawing showing sequential double training. B, C, Sequential double training in the single staircase condition. Eleven subjects were first trained with Vernier stimuli at ori1_loc1 (blue circles) and then sequentially at ori2_loc2 (magenta circles). Transfer of Vernier learning was measured at ori1_loc2 in pre-, mid-, and post-testing sessions (green circles). Sequential location training (ori2_loc2) did not induce transfer of Vernier learning to untrained locations (ori1_loc2, second and third green circles in B; right green bar in C). Bars in the mid-test and post-test indicate threshold differences between the pre- versus mid-test, and mid- versus post-test, respectively. D, E, Sequential training in multiple short staircase condition. Contrary to A and B, sequential location training (ori2_loc2) enabled transfer of learning to ori1_loc2 in this multiple short staircase method (the second and third green circles in D; right green bar in E).