A, ITD jnds using midline reference point (zero ITD). Solid, upward trianglesindicate an increase in firing rate (i.e., 75% correct).Open, downward triangles indicate a decrease in firing rate (i.e., 25% correct). Small,filled circles are ITD jnds using the reference point chosen to yield best jnd, joined to the corresponding midline jnds bylines. B, Comparison of ITD jnds obtained using reference point giving best jnd (abscissa) and those obtained using midline reference point (zero ITD:ordinate). The diagonal line marks equality between jnds.