James A. Simmons

Ph.D., Princeton University, 1969
Professor
Department of Neuroscience
208 Medical Research Laboratory
and Hunter Laboratory
Tel. (401) 863-1542

Research Summary

My laboratory studies the biological sonar, or echolocation, of bats as an auditory imaging system. The research uses behavioral, neurophysiological/ neuroanatomical, and modeling techniques to learn how bats process echoes of their ultrasonic sonar transmissions to perceive the location and identity of the flying insects they prey upon. The approach is a combination of neuroethology and systems neurobiology, with sonar signal-processing as a theoretical tool. Presently, we are carrying out experiments on target ranging by the big brown bat, Eptesicus fuscus, to characterize the images bats perceive along the dimension of echo delay or target distance. Eptesicus transmits frequency-modulated (FM) sonar sounds and perceives the delay of echoes from the timing of neural discharges they evoke in the auditory system. The bat perceives the shape of targets from the spectrum of echoes, but the images themselves consist of a reconstruction of the differences in range to the different parts of the target (for example, an insect¹s head and wing). Thus, the image has echo delay as its primary dimension, both for determining how far targets are from the bat and for determining their shape. The auditory cortex of Eptesicus appears to carry out the neural computations that transform the echo spectrum into estimates of the distance to the different parts of the target,and we are presently investigating the response properties of cortical neurons in relation to the delay and spectrum of FM echoes. This problem is of considerable theoretical interest because the bat carries out parallel time-domain and frequency-domain transforms to form its images of targets. We use a large-scale parallel, distributed model of the bat¹s sonar receiver to identify critical parameters of neural responses which are relevant for carrying out these transforms, and then we record the responses of cortical neurons to sonar signals and echoes as a means of evaluating the model.

Publications

Simmons, J.A., Saillant, P.A. and Dear, S.P. (1992) Through a Bat's Ear. IEEE Spectrum (March 1992):46-48.
Simmons, J.A., Ferragamo, M., Moss, C.F., Stevenson, S.B. and Altes, R.A. (1990) Discrimination of jittered sonar echoes by the echolocating bat, Eptesicus fuscus: The shape of target images in echolocation. J. Comp. Physiol.-A 267:589-616.
Simmons, J.A. (1989) A view of the world through the bat's ear: The formation of acoustic images in echolocation. Cognition 33:155-199.

Sonar signal and echo reflected by a flying moth, together with auditory system's spectogram representation of waveforms.