Sydney Frank Hall
We maintain a colony of Eptesicus fuscus
in a fully equipped animal-husbandry facility, including a big flight cage. Temperature and humidity are closely controlled to maintain a suitable climate for bats. The bat care facility is equipped with a separate HVAC system that isolates airflow with a hepafilter. The bat colony is a level 2 biohazard facility that isolates bats as a precaution against the spread of rabies.
psychophysical experiment setup:
Platform behavioral experiments are conducted with a psychophysical apparatus that receives bat echolocation signals and returns electronically generated and manipulated echoes from electrostaic loudspeakers. Bats crawl down the platform that is located in the corner of the room, and are trained to respond to and differentiate electronic echoes with special temporal and spectral characteristics. The bats own broadcast is being electronically changed in a way that we can manipulate different characteristics of echo being played back to the bat. The surrounding walls of the room are lined with acoustic foam to reduce reverberation. The room itself is covered with a layer of copper paint to ensure that no interfering signals enter while performing experiments. Experiments are conduced in low light conditions to reduce extraneous visual cues. Echoes are recorded with microphones positioned at the end of each path of the Y-shaped platform. The signals are processed with custom designed electronic equipment in the neighboring suite, and the broadcasts are returned to bat through loudspeakers mounted next to each microphone.
bat flight room:
Free-flight behavioral experiments are conducted in an acoustically and radio-frequency shielded flightroom (8 X 3 X 2.7 m). The flightroom is designed for obstacle-avoidance experiments, which challenge the bats to navigate in the dark through a cluttered environment. Bats are released inside the chamber and fly through mazes configured out of columns of vertical plastic chains suspended from the ceiling.
The flightroom is equipped with an array of 24 ultrasonic microphones distributed along the walls of the room. Each microphone unit consists of a Knowles MEMS electrical microphone mounted on a custom designed circuit board with an onboard power supply signal amplifier. The signals from microphone array are recorded with a MOTU audio-video system and digitized to computer along with video feed from a pair thermal-imaging infrared cameras that see the bat from it's body heat.
The data from the acoustic recording are processed using a custom written MATLAB routine that tracks the bats in 3D using passive acoustic localization (cf. field array recording). The signals from all 24 microphones are combined through near field beamforming, creating a virtual telemike that is focused on the position of the bat. These custom signal processing techniques allow us to produce an acoustic record of the bat's echolocation behavior that is unbiased by Doppler Shifts
and atmospheric attenuation. The amplitudes of the signals arriving at each member of the array are also used to measure the bat's headaim and the frequency dependent shape of the beam aim in each broadcast.
neurophysiological recording rigs:
We conduct neurophysiological experiments using in vivo
and in vitro
recordings are conducted with extracellular electrodes, with the animals positioned inside of a sound-proof booth. The recordings are controlled with custom written LabVIEW software that generates acoustic stimuli and records neural signals using a National Instruments PXI analog-to-digital interface. Depending on the experimental configuration, we record with one or multiple electrodes optimized for either local field potential or single unit recordings. In vivo
recordings are also used to guide ionophoretic injections of tract tracing dyes into auditory structures of the brain.
recordings are performed in slice preparations using extracellular and intracellular electrodes and voltage sensitive dye techniques. In vitro
recordings are performed under a fluorescent microscope while data are recorded using a dedicated Apple Mac Pro computer.
field array recording:
We conduct experiments in the field using an array of 10 ultrasonic microphones from which we record using a pair of measurement Computing analog to digital boxes and a IBM laptop computer. The microphone array is erected on specially designed microphone towers distributed throughout a recording site. The positions of the microphones are measured using a Sokkia theodolite (Total Station) signals from the microphones are processed using custom MATLAB routines to localize one or multiple bats in 3D, and analyze the temporal and spectral structure of their sonar broadcasts. Our field recording setup is highly portable and has been used in the Central American jungle, Singapore as well local sites in Southern New England.
dense microphone array aka the arrayzilla:
To probe the shape of the bat's broadcast beam, we use a densely populated 216-microphone planar array. The array is 1.8 m X 1.4 m, mounted about 1 m from the bat and oriented perpendicular to the sound's axis. Specially built amplification, filtering, and digitizing circuits store the signals recorded by the all 216 microphones. Custom written MATLAB routines localize the sound source and reconstruct the beam's cross-sectional profile of amplitudes at different frequencies.
graduate student office:
Graduate students are assigned a workspace in our student office and are provided with a Dell personal computer for data analysis. In addition, we maintain a motley inventory of customized computers, data capture devices, digital electronics, and analog electronics customized to our experiments and data needs.
2 X Merlin Indigo Systems, Inc., (Now FLIR) midrange thermal-imaging infrared video cameras
2 Proton (FLIR) thermal imaging video camera (lightweight for field use)
4X SONY Digital video Walkman VCRs
1X SONY SIR-1000W digital instrumentation recorder
1X Sound Devices T202 DAT recorder
8X B&K Model 4136 or 4138 condenser microphones, with matching B&K preamplifiers and power supplies
Two-channel electronic target simulator system, with 3 digital delay-lines (12-bit accuracy. 0-36000 microseconds in 1.3 microsecond steps) and 3 analog delay lines (0-100 microseconds in various combinations with steps from 1 nanosecond to 20 microseconds)
4 WaveTek-Rockland Model 753A analog 115-dB/oct high/low/bandpass filters
4 Rockland Model 442 analog 48 dB/oct high/low/bandpass filters
6 Dell or Gateway Pentium-4 personal computers with a variety of digital data-acquisition boards, software for acoustic analysis, motion analysis, statistics, signal-processing, etc.
Quantities of analog oscilloscopes (Tektronix Type 2236 and 2245), wideband power amplifiers (Krohn-Hite Model 7500), signal generators, decibel-scale attenuators, VCRs, video cameras, ultrasonic loudspeakers, etc.
Even larger quantities of obsolescent but perfectly useful analog electronic equipment, including apparatus for calibration and repair of electronic equipment