Studying dolphin biosonar with the jittered-echo paradigm

Abstract

In his 1979 paper “Perception of echo phase information in bat sonar” [Science 204, 1336–1338], Jim Simmons introduced the “jittered-echo” paradigm. In this method, bats discriminated between electronic echoes with fixed delay (i.e., simulating fixed range) and those with delays that alternated (“jittered”) on successive echoes. The jittered-echo paradigm was developed to minimize the interfering effects of head movement, under the assumption that head movement between successive pulse emissions is negligible. Echo delay thresholds obtained with the jitter technique are small, with multiple studies reporting sub-microsecond echo delay thresholds in the big brown bat. The jitter method has also been controversial, because of the extremely low echo delay resolution (10 ns) and sensitivity to echo phase (fine structure) reported by Simmons. Recently, the jitter delay paradigm has been adapted for underwater use with dolphins. Results with dolphins show qualitative similarities to those from bats: echo delay thresholds below 1 μs and sensitivity to echo fine structure. This talk will briefly review Simmons’ and other’s biosonar jitter experiments with bats, then present in detail experiments with bottlenose dolphins featuring jittered echo delay and phase.