plished by flicking, (iii) that the maximum observed flick rate of 4 Hz corresponds to the neurophysiologically determined flicker fusion frequency of olfactory receptor cells, (iv) that receptor cells are tuned not only to specific compounds but also to different temporal parameters of odor, and (v) that lobsters locate odor sources with search paths, walking speed, and turning behavior suggestive of chemotaxis based on patchy odor distributions. These results show that turbulently dispersed odor patches from a single source contain spatial gradients of signal parameters and that some of these parameters are recognized by olfactory temporal filters. We hypothesize that these temporal odor parameters provide information for chemotactic navigation in odor plumes. At this point, we have learned some of the physiologically determined temporal filters, but we do not know the exact nature of the behaviorally relevant signal features nor the sampling regimes and signal processing required to lead to efficient navigation. We are approaching these questions with behavioral, physiological, computational (19), and robotic methods (20). In the context of pheromone communication, Bossert (21) calculated that amplitude modulation could enhance information transmission very significantly. Some moths release pheromone in puffs with 1-s periodicity (22) and it was found that Bossert's calculations must be reevaluated in light of current knowledge of temporal filter properties of chemoreceptor cells and the unpredictability factor of turbulent dispersal that characterizes most natural environments.

SIGNAL PRODUCTION AND BROADCASTING: URINE DISPERSAL IN CHEMICAL COMMUNICATION

This section reviews the complex currents lobsters generate to eliminate metabolites and broadcast chemical signals and the return currents from which they obtain chemical signals and metabolic energy. Lobsters are examples of hard-shelled animals that store urine and feces, allowing them to be chemically "quiet" when necessary.

Information Currents and Urine Signals

H. americanus utilizes three current-generating mechanisms that can operate separately or in combination; all three are implicated in chemical communication. The scaphognatites inside the gill chambers generate a powerful gill current which jets forward from bilateral "nozzles." This current reaches distances of up to seven body lengths in adults (2) and velocities of 3 cm/s near the nozzle. It is usually a bilateral current and it carries the animal's gill metabolites. Mature-sized lobsters under summer temperatures rarely cease producing this breathing current; in winter, the



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