Spatially-limited attention to vibrotactile stimulation

Weak vibrotactile signals were presented to human Os, in some instances to the index finger alone, in other instances to the middle finger alone, and in still other instances to the two fingers simultaneously. When the 0 knew in advance of a trial which finger(s) would be presented a signal, no spatial summation resulted, that is, the sensitivity of two fingers to two signals was no greater than the sensitivity of one finger to one signal. When the 0 was left uncertain about which finger(s) would be presented a signal on any given trial, a result having the appearance of spatial summation was obtained. Theappearance is misleading;the difference between two-finger and one-finger sensitivity in this case reflects, instead, a decrement in the performance of the single fingers. Both results are consistent with a single-channel model of attention.