Stimulus Intensity and Spatiality in Tactile Temporal Numerosity Discrimination

The role of signal intensity in tactile temporal numerosity discrimination was investigated for limited conditions of signal number and presentation rate. Trains of 5 to 18 mechanical ‘taps’ were presented at rates of 6, 8, 10, 12, or 15 s−1 to the ball of the left middle finger at either 75 or 125 V (15 or 20 dB SL, respectively). Trains of signals of greater intensity were counted reliably more accurately. Results from this spatially static arrangement are compared to those obtained under conditions of spatial variation where signals of identical intensity were delivered to multiple loci instead of to a single locus. It is concluded that the absolute judgment of the number of tactile signals in a train is a very labile process and highly dependent upon, and specific to, the physical characteristics—temporal, spatial, and intensive—of the stimulus complex.