Guest Seminar: Dr. James Simmons
“Bat Sonar, Clutter and Engineering”
Dr. James Simmons, Professor of Biology
Wednesday, September 21, 2016 at 2:00 p.m.
Kelley Hall, Room 102
Echolocating bats transmit wideband FM biosonar signals in the 20-100 kHz frequency band and hear echoes to guide flight and form images of targets. They use a time-frequency signal representation with unusual parallel architecture based on the inner ear’s frequency-tuned receptors. Bats determine target range from the elapsed time between corresponding frequencies in broadcasts and echoes. Targets return echoes with spectral characteristics that represent the contributions of reflections from several prominent points, or glints, within the target. Using auditory computational advantages, they transform echo spectra into deconvolved images of the target’s glints, which leads to novel target-based synthetic-aperture images. A target is tracked to keep it on the broadcast beam, which ensures that all of the frequencies in the incident sound impinge on the target at full strength. As a result, the images are sharply focused. Echoes from offside clutter are lowpass-filtered due to directional beaming. For clutter, the auditory deconvolution mechanism yields blurred, defocused images, which do not interfere with perception of focused target images. The role of neural spike timing on image content reveals an important aspect of how attention to objects is mediated in the brain.