From sperm-whale clicking to human finger-tapping. An etho-mimetic model for rhythms of active reception

Motor rhythmic activities are involved in sensorimotor processes. Active reception is the process by which an agent extracts information about the surroundings from self-emitted probe signals. Human haptics, mammal echolocation and fish electrolocation are among the most documented functions in nature; man has developed radar, sonar and magnetic resonance imaging set-ups. Sperm whales (Physeter macrocephalus) use an echolocation system based on clicks emitted at variable rhythms. During navigation, their clicking rate increases when they arrive in their foraging zone, and turns into bursts called "creaks" when attaining their prey (ref). Due to convergent evolution, analogous accelerations in the emission of transient probe signals are observed in other animals that use active reception such as dolphins, echolocating bats and mormyrid electric fish.

We wanted to see if humans, enabled to use an echolocation system, would spontaneously show similar phases of sequences of pulse intervals when approaching a target. In our etho-mimetic paradigm, human participants - eyes closed - navigated around on a table by tapping on it with a thimble at the tip of their index finger and listening to the specific sound feedback produced on different areas. A part of the table top covered by a layer of thin paper mimicked the hunting zone. Distributed over it, a number of (“prey”) targets consisted in paper disks stuck over the layer. Their orientation (parallel vs orthogonal to the table width) was drawn by a thin strip underneath along one of their diameters.

The rhythms of probing were analyzed through the inter-tap intervals, analogous to sperm inter-click intervals. First, results show that humans are definitely able to use echolocation for fine perception tasks. Second, the tapping rates they displayed along the successive phases were in accordance with the supposed function respectively associated (navigating, hunting, discriminating). The rhythms were much comparable with those of other animals using active reception (pulse electric discharges, sonic clicks). In particular, a drastic speed-up occurred at the time of determining the target’s orientation, similar to sperm whales’ “creaks” before attack, discharge “bursts” of mormyrid foraging on a worm and bats’ “final buzz before an insect catch. Furthermore, the speed-up profile was proportionally the same for all participants. Our etho-mimetic approach highlights spontaneous human features in an analogous situation and confirms our understanding of animal behavior. It illustrates the relationship between time and space by the advantage of a higher sampling rate for a finer spatial resolution.