Selective spatial attention has a greater effect on detection of the absence of an amplitude change than it has on detection of the presence of such a change. Attention to one of four fingertips was manipulated by an 80% valid tactile cue in two-interval forced-choice tasks. In one task, the target was a vibrotactile amplitude change appearing among constant- amplitude distractors; in the other task, targets of constant amplitude had to be detected amid amplitude changes at the other fingertips. Cuing had a greater effect on the latter task than it did on the former. This asymmetry is consistent with the presence-absence asymmetry found in visual search and does not depend on the difficulty of the two tasks. A statistical model shows that a pooled activity mechanism could account for these experimental results.