KILLER WHALE (ORCINUS ORCA) AUDITORY EVOKED POTENTIALS TO RHYTHMIC CLICKS |
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Authors: | M. D. Szymanski A. YA. Supin D. E. Bain K. R. Henry |
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Affiliation: | Department of Neurology (127) VA Medical Center, 150 Muir Road, Martinez, California 94553, U. S. A. E-mail:;Institute of Ecology and Evolution of the Russian Academy of Sciences, 33 Leninsky Prospect, 117071 Moscow, Russia;Marine World Foundation, Vallejo, California 94589, U. S. A.;Department of Psychology, University of California Davis, Davis, California 95616, U. S. A. |
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Abstract: | Temporal auditory mechanisms were measured in killer whales ( Orcinus orca ) by recording auditory evoked potentials (AEPs) to clicks. Clicks were presented at rates from 10/sec to 1,600/sec. At low rates, clicks evoked an AEP similar to the auditory brainstem response (ABR) of other odontocetes; however, peak latencies of the main waves were 3–3.7 msec longer than in bottlenose dolphins. Fourier analysis of the ABR showed a prominent peak at 300–400 Hz and a smaller one at 800–1,200 Hz. High-rate click presentation (more than 100/sec) evoked a rate-following response (RFR). The RFR amplitude depended little on rate up to 400/sec, decreased at higher rates and became undetectable at 1,120/sec. Fourier analysis showed that RFR fundamental amplitude dependence on frequency closely resembled the ABR spectrum. The fundamental could follow clicks to around 1,000/sec, although higher harmonics of lower rates could arise at frequencies as high as 1,200 Hz. Both RFR fundamental phase dependence on frequency and the response lag after a click train indicated an RFR group delay of around 7.5 msec. This corresponds to the latency of ABR waves PIII-NIV, which indicates the RFR originates as a rhythmic, overlapping ABR sequence. The data suggest the killer whale auditory system can follow high click rates, an ability that may have been selected for as a function of high-frequency hearing and the use of rapid clicks in echolocation. |
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Keywords: | killer whale Orcinus orca hearing auditory brainstem response brain spectral analysis rate |
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