An ear for crime

November 22, 2004

A University of Southern California biomedical engineer's pioneering brain cell research has led directly to a patented system that is now being rolled out to stem gun violence on the streets of Chicago and Los Angeles.

The engineer is Theodore Berger, director of the USC Center for Neural Engineering whose life's work has been deciphering the way in which nerve cells code messages to each other.

Now, a camera-and-microphone surveillance system is using his insights to recognize -- instantly, and with high accuracy - the sound of a gunshot, and only a gunshot within a two-block radius.

It can then locate, precisely, where the shot was fired; turn a camera to center the shooter in the camera viewfinder, and make a 911 call to a central police station. The police can then take control of the camera to track the shooter and dispatch officers to the scene.

The city of Chicago is now installing the first five of 80 of the devices in high crime neighborhoods. In Los Angeles County, Sheriff Lee Baca is now soliciting community involvement and participation to deploy 10 of the units in a pilot test, to be followed by more if the results are successful.

Algorithms devised by Berger, who hold the David Packard Chair in the US Viterbi School of Engineering's department of biomedical engineering, are at the heart of the "SENTRI" system built by an Oak Brook, Illinois-based firm named Safety Dynamics, a company in which Berger holds the position of Chief Scientist.

SENTRI uses acoustic recognizers, posted in trios or larger groupings on utility poles or other listening posts, which are tuned to certain specific warning sounds with extremely high accuracy. "A simple loud noise, even an explosive noise, won't set them off,"

The device is listening for the entire sound pattern of the gunshot, not just the initial explosion, which makes it much less likely to mistake other loud noises for shooting.

A specially configured computer system (a "directional analyzer") accurately calculates any authenticated gunshot's location - using the difference in the time the sound arrives at the different microphones on a SENTRI acoustic units unit. It then points a camera, turns on lights, sounds an alarm, and alerts police units.

Field tests with real guns (45 cal, 38 cal, 9 mm) have shown 95% accuracy with respect to gunshot recognition, and 100% accuracy with respect to centering the camera on the shooter for those recognized gunshots.

SENTRI is an acronym for "Smart Sensor Enabled Neural Threat Recognition and Identification." The "neural" in the title refers directly to Berger's work, which was based on analysis of the "language" nerve cells, or neurons, use to convey information, and specifically on his modeling of the way the brain forms memories of sounds

Neurons only way of distinguishing signals is to fire repeatedly, either faster or slower, in different temporal patterns. "It is the time difference between pulses that carries the information," Berger says. "This is a coding completely unlike that used by computers, which are collections of ones and zeros, changing to the beat of a constant clock."

Working with computer specialists, however, Berger has created neural-like computer systems that can model the neural time coding and make distinctions the way nerves do.

Four years ago, he and a colleague used the technique to demonstrate the first speech recognition system that could pick words out of ambient noise as well as humans can.

While work continues on speech recognition applications, the systems need training to learn individual signals, and this is time consuming, since for language each individual word has to be taught.

"But for alarm signals," says Berger, "you start with a relatively small number of sounds you have to distinguish with high accuracy - gunshots, for example, or diesel engines for border patrol crossings or oil pipeline thieves, or chainsaws (and diesels) to listen for outlaw loggers. This vocabulary is quite manageable."

Machine sounds are the only ones in SENTRI's vocabulary. It cannot eavesdrop on conversations, the scientist emphasizes.

Berger's work with neural systems grows directly out of thirty years of research attempting to create a silicon system that can be transplanted into living brain or other nervous tissue to restore function lost to disease or injury.

University of Southern California

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