Frequency tuning of hearing in the beluga whale: Discrimination of rippled spectra

Abstract

Frequency tuning was measured in the beluga whale (Delphinapterus leucas) using rippled-noise test stimuli in conjunction with an auditory evoked potential (AEP) technique. The test stimulus was a 2-octave-wide rippled noise with frequency-proportional ripple spacing. The rippled-noise signal contained either a single reversal or rhythmic (1-kHz rate) reversals of the ripple phase. Single or rhythmic phase reversals evoked, respectively, a single auditory brainstem response (ABR) or a rhythmic AEP sequence-the envelope following response (EFR). The response was considered as an indication of resolvability of the ripple pattern. The rhythmic phase-reversal test with EFR recording revealed higher resolution than the single phase-reversal test with single ABR recording. The limit of ripple-pattern resolution with the single phase-reversal test ranged from 17 ripples per octave (rpo) at 32 kHz to 24 rpo at 45 to 64 kHz; for the rhythmic phase-reversal test, the limit ranged from 20 to 32 rpo. An interaction model of a ripple spectrum with frequency-tuned filters suggests that the ripple-pattern resolution limit of 20 to 32 rpo requires a filter quality Q of 29 to 46. Possible causes of disagreement of these estimates with several previously published data are discussed.

Design and Evaluation of a USB Isolator for Medical Instrumentation

“…However, the usage of medical grade isolation transformers reduces the portability in the PC and the batteries limit the time of use of ME. Other designs use isolation amplifiers [11]- [13], isolation transformers [14], [15], or sensors that use insulating materials [16]- [18] in the signal acquisition stage of the ME. Although these provide electrical protection for the patient, the operator is at risk if there are no other isolation media to protect him/her from electric shock.…”