Assessing continuous sensory information encoding capacity by a biomimetic dynamic sonar emitter

Bat species in the rhinolophid and hipposiderid families can deform the shapes of their noseleaves (ultrasonic emission baffles) in synchrony with emission of the biosonar pulses. Prior work has shown that these physical deformations of a diffracting baffle can add a time-variant quality to the emitted pulses. Whereas conventional sonar emitters can be characterized by gain values that are functions of direction (e.g. azimuth and elevation) and frequency only, the biosonar emission characteristics in these bat species is a function of direction, frequency, and time. Prior work has indicated that the unique emission time variance seen in the bats could support the encoding of additional sensory information. In the work presented here, a biomimetic noseleaf has been used to collect a densely sampled representation of a time-variant emission characteristics. This data set has been analyzed using advanced (nearest-neighbor based) estimators for information theoretic measures such as mutual information and relative entropy. The findings from this analysis suggest three hypotheses regarding the nature of these biomimetic time-variant emitter characteristics: (i) its complexity reflects all independent physical dimensions (ii) coding capacity along the time and frequency dimensions does not differ substantially, and (iii) sensory information is accumulated continuously along a time-variant pulse.