Spatial organization of the diplesthetic and nondiplesthetic areas of the fingers.

Cutaneous points on different fingers were brought into contact with each other to ascertain whether one stimulus was perceived to be single or double. The perceptual responses were mapped on the five fingertip pads. The results show that there is an extensive cutaneous area on each fingertip pad which elicits one-stimulus perceptions when a single stimulus is applied between each finger and the thumb. This area decreases when the stimulus is applied to adjacent fingers (2-3, 3-4, 4-5), and even more so when it is applied to nonadjacent fingers (2-4, 2-5, 3-5). In fact, in adjacent and nonadjacent fingers the cutaneous surface eliciting a doubling of the single stimulus (diplesthesia) is very extensive. The spatial arrangement of the cutaneous areas eliciting single perceptions appears to be invariant in the proximo-distal plane. Instead, the shift from one kind of perception to another occurs in the medio-lateral plane. It is suggested that this perceptual organization could reflect a neural organization.