Multidigit tactile perception II: perceptual weighting during integration follows a leading-finger priority.

When we run our hand across a surface, each finger typically repeats the sensory stimulation that the leading finger has already experienced. Because of this redundancy, the leading finger may attract more attention and contribute more strongly when tactile signals are integrated across fingers to form an overall percept. To test this hypothesis, we re-analyzed data collected in a previous study (Arslanova I, Takamuku S, Gomi H, Haggard P, 128: 418-433, 2022), where two probes were moved in different directions on two different fingerpads and participants reported the probes' average direction. Here, we evaluate the relative contribution of each finger to the percept and examine whether multidigit integration gives priority to the leading finger. Although the hand actually remained static in these experiments, a "functional leading finger" could be defined with reference to the average direction of the stimuli and the direction of hand-object relative motion that this implied. When participants averaged the motion direction across fingers of the same hand, the leading finger received a higher weighting than the nonleading finger, even though this biased estimate of average direction. Importantly, this bias disappeared when averaging motion direction across the two hands. Both the reported average direction and its systematic relation to the difference between the individual stimulus directions were explained by a model of motion integration in which the sensory weighting of stimuli depends on the directions of the applied stimuli. Our finding supports the hypothesis that the leading finger, which often receives novel information in natural hand-object interactions, is prioritized in forming our tactile perception. The capacity of the tactile system to process multiple simultaneous stimuli is restricted. One solution could be to prioritize input from more informative sources. Here, we show that sensory weighting accorded to each finger during multidigit touch is biased in a direction-dependent manner when different motions are delivered to the fingers of the same hand. We argue that tactile inputs are weighted based on purely geometric information to prioritize "novel" information from the leading finger.