Comparison of difference limen (DL; with s.e. bars) between the Control and DXM groups for amplitude discrimination with single-site adaptation at times T0, T1, and T2. No adapting stimulus was applied to either stimulus site in Block 1, and no difference was observed between the two groups at any time for Block 1. The test condition in Block 2 was preceded by an adapting stimulus (1 sec in duration) at the site of the test stimulus. Note that at T1, in Block 2, performance between the groups was significantly different (* ANOVA; p < 0.01). At T2, Block 2 performance values for the DXM group return to baseline levels (p = 0.092).