The basic setup of an electronic echo experiment. The bat's calls are picked up by microphones (m), electronically delayed and manipulated, and returned to the bat through a speaker (s). Bats are trained to distinguish between a positive stimulus (S+) and a negative stimulus (S-). These experiments allow us to understand how bats echolocate in a cluttered environment.

Our lab uses psychophysical experiments to investigate the perceptual abilities and limits of echolocating bats. We have developed a system using electronically-generated echoes as stimuli, rather than physical objects, to test the bats' responses to different characteristics of echoes.

Bats are trained with positive reinforcement to sit on an elevated Y-shaped platform and emit echolocation sounds towards the two ends. Their sounds are picked up by microphones located at the end of each arm, delayed electronically, filtered, and then delivered back to the bat from speakers at the ends of each arm to simulate an echo returning from an object at a certain distance. The bat is rewarded with food when it walks down the arm of the Y-platform corresponding to the positive, or rewarded, stimulus.

The use of electronically-generated echoes allows us to have more control over the stimuli the bats receive. For example, we can control the delay time, amplitude, and spectral content of the echoes. We can even manipulate the echoes in ways that would never occur naturally (for example, removing frequency bands or delaying the harmonics within a single sound differently). The bats' performance, measured in percent errors, tells us about how the bats perceive different attributes of echoes and how echo characteristics are used to determine the distance, shape and direction of a target.

Big brown bat (Apollo) performs the electronic echo task.

We're interested in learning how bats distinguish echoes from their own sounds from the sound-echo pairs of other bats (jamming avoidance) and how they detect the echoes of targets amidst competing echoes from background objects (clutter rejection). Both jamming avoidance and clutter rejection require the bat match a template of its emitted sound to a returning echo. The psychophysical experiments allow us to test how bats perceive echoes that do not match their emitted sound. We've found that bats can detect very small deviations in time-frequency structure between emitted sounds and received echoes, and that these deviations affect echo-delay acuity and masking.

Further Reading:
Bates and Simmons (2010) JASA
Bates and Simmons (2011) JEB