Discrimination of two-wavefront echoes by the big brown bat, Eptesicus fuscus: behavioral experiments and receiver simulations.

1. Echolocating bats (Eptesicus fuscus) were trained to discriminate between simulated targets consisting of one or two echo-wavefronts with internal time delays of up to 100 microseconds. Spectral and temporal properties and total signal energy of the targets were evaluated and predictions for performances of bats derived from receiver models were compared with measured performances. 2. Eptesicus fuscus was able to discriminate a one-wavefront target from two-wavefront targets with distinct internal time delays (12 microseconds, 32-40 microseconds and 52-100 microseconds). Performance was not affected by changes in total signal energy. Bats also successfully discriminated between two-wavefront targets with different internal time delays. 3. Performance predicted from differences in total energy between targets did not match the measured performance, indicating that bats did not rely on total echo energy. This finding is also supported by the behavioral data. Performance predicted from spectral and temporal receiver models both matched the measured performance and, therefore, neither one of these models can be favored over the other. 4. The behavioral data suggest that Eptesicus fuscus did not transform echo information into estimates of target range separation and, therefore, did not perceive the two wavefronts of each simulated two-wavefront echo as two separate targets.