We investigated competitive neural interactions for processing resources during sustained spatial attention in somatosensation. Participants received concurrent vibrotactile stimulation at different frequencies to either non-adjacent left hand fingers (within-hand) or fingers on two hands (between-hands) for 4500 ms to elicit steady-state somatosensory evoked potentials (SSSEPs). They attended to either one or both stimulated locations, respectively, and responded to rare events embedded in the ongoing stream. Behavioral and electrophysiological results revealed competitive interaction of simultaneous stimulation with overall smaller SSSEP amplitudes and poorer behavioral performance in the within-hand condition. Spatial proximity of stimulation did not affect the magnitude of attentional gain, it resulted in the occurrence of an intermodulation frequency indicating integrative stimulus processing in the within-hand condition. Obviously, while this integrative stimulus processing resulted in or was a result of greater intra-hemispheric competitive interactions, attention acted additively as a signal gain, which was independent of spatial competition.