ASA 124th Meeting New Orleans 1992 October

4aPP7. Ultrasonic down-conversion in canine hearing sensor.

Edward L. Fink

Command K-9, 425 S. Valley, Ridgecrest, CA 93555

Hearing threshold frequency response curves over range 2--100 kHz are reported for a group of dogs. Eight conditioned reflex techniques with different behavior paradigms were utilized. All techniques produced a curve that is unsymmetrical about primary resonance minimum and had a secondary resonance minimum and maximum peak. The position of the peaks varied with the paradigm. Comparison of the curves with models of cochlea dynamics showed that experimental data is best fitted with a model having a 0.35--0.5 power-law generation term which represents subharmonic frequency generation (i.e., down-conversion), by basilar membrane, which is in resonance with a secondary resonance structure. Additional evidence is presented for a subharmonmic generation mechanism comprising the simultaneous impression of 44 kHz and a lower amplitude 22-kHz sound via an ultrasonic transponder collar. The 44-kHz threshold was raised when the 22-kHz sound had a negative phase. Neural center involvement in forming secondary peaks was explored by measurements of EEG evoked potentials and a drug modification effect. EEG measurements revealed an echo which was delayed from the initial nerve pulse, and lithium, which is limbic specific, injection had the effect of smoothing or eliminating secondary peaks in threshold curve. These results suggest two areas of memory being active and interfering with one another, one of them being located in the limbic, instinct center.