SUMMARY
Active sensing is the production of motor signals for sensing [1–5]. The most common form of active sensing, found across animal taxa and behaviors, involves the generation of movements—e.g. whisking [6–8], touch [9, 10], sniffing [11, 12], and eye movements [13]—that shape spatiotemporal patterns of feedback. Despite the fact that active-sensing movements profoundly affect the information carried by sensory feedback pathways [14–16], how such movements are regulated remains poorly understood. To investigate the control of active-sensing, we created an augmented reality apparatus for freely swimming weakly electric fish, Eigenmannia virescens. This system modulates the gain of reafferent feedback by adjusting the position of a refuge based on real time videographic measurements of fish position. We discovered that fish robustly regulate sensory slip via closed-loop control of active-sensing movements. Specifically, as fish performed the task of maintaining position inside the refuge [17–22], they dramatically up-or down-regulated fore-aft active sensing movements in relation to a 4-fold change of experimentally modulated reafferent gain. These changes in swimming movements served to maintain a constant magnitude of sensory slip. The magnitude of sensory slip depended on the presence or absence of visual cues, but in each condition the respective magnitude was maintained across reafferent gains. These results indicate that fish use two control loops: an “inner loop” that controls the acquisition of information by regulating sensory slip, and an “outer loop” that maintains position in the refuge, a control topology that may be ubiquitous in animals [23, 24].