Figure 4.

Schematic representation of turbulent plume features proposed as potentially relevant to plume tracking, including odor pulses and odor gaps separated by the background odor concentration that gradually increases with decreasing distance to the source (lemon fruits). A cockroach walking toward the source will perceive the spatial distribution of odor concentration as temporal concentration change. By using simultaneous or successive sampling strategies, concentration differences determined by bilateral comparison of the responses of ON and OFF ORNs on both antennae will guide the cockroach to move forward or return to the previous position. Response bias for equal-amplitude concentration drops relative to jumps enhances detection of low concentration change with rising background level. Therefore, the OFF responses are used as alert information for accurately tracking motion.