- Here we describe a nonsynaptic mechanism for filtering out potentially perturbing sensory feedback during locomotion. During flight, the cockroach moves its cerci, two abdominal sensory appendages, about their joint with the body and holds them in place. The cerci bear highly sensitive wind-receptive hairs, which would be strongly stimulated by flight wind. Such wind could cause habituation of the synaptic connections from these cercal receptors onto interneurons responsible for the running escape response to an approaching predator. We have found that the cercal displacement blocks one-third to one-half of the action potentials along the sensory nerve, possibly aiding in protection against such habituation. This block occurs if one experimentally displaces a cercus, and the block persists in the complete absence of any connections with the central nervous system. The block appears to be nonsynaptic and to result instead from mechanical pressure on the nerve near the joint. The results suggest that activity in peripheral nerves in other animals may also be affected by the position or movement of joints through which the nerves pass.