California sea lion (Zalophus californianus) aerial hearing sensitivity measured using auditory steady-state response and psychophysical methods
Transmitting voltage response for the Sennheiser HDA 200 headphones used in psychophysical and electrophysiological audiometric procedures with a 1.5-yr-old California sea lion. The curve was generated by calibrating stimuli with a probe microphone while the headphones were worn by California sea lions. The increased variability at the higher frequencies is most likely due to small changes in the placement of the probe microphone and the headphones. Symbols indicate the mean of three measurements, and error bars show the SD.
Noise levels inside the (a) testing environment used for psychophysical testing and (b) veterinary clinic used for electrophysiological testing. Bars indicate the 10th, 50th, and 90th percentile levels, and the 1-min L eq for each 1/3-octave band.
Psychophysical and ASSR aerial audiograms for a 1.5-yr-old California sea lion. The single and multiple ASSR methods provided equivalent thresholds. Both methods provide a good approximation of the psychophysical audiogram. Note the increased discrepancy of the psychophysical and electrophysiological thresholds at the low and high ends of the audiogram. The multiple ASSR thresholds are shifted along the frequency axis for clarity. Symbols indicate the mean threshold for each method. The error bars are based on the combined SDs of the thresholds and the transmitting voltage response of the headphones (see text).
Spectra of ASSR waveforms obtained during a multiple ASSR audiometry procedure with a 1.5-yr-old California sea lion. The carrier frequencies of the SAM components are shown at the top of the figure, and dashed lines underneath the center frequencies indicate the modulation rate that was imposed on the stimulus (see Table II). The peaks at each of the modulation rate indicate the presence of ASSRs evoked by the SAM stimulus. The levels of the stimuli were adjusted independently in order to determine threshold (see text).
Mean aerial psychophysical hearing thresholds (in dB SPL) and SDs for a 1.5-yr-old California sea lion. Also shown are the number of reversals included in analysis, and the subject’s FA rate for each frequency. Asterisks indicate that FAs only occurred during the final session conducted for a particular frequency (see text).
Aerial hearing thresholds (in dB SPL) for a 1.5-yr-old California sea lion, obtained using single and multiple simultaneous ASSR methods. The data represent 2 days of electrophysiological testing, each of which included one single and one multiple simultaneous ASSR audiometry session. The rate of AM used for each frequency component is also shown. Threshold testing at 22 kHz was included during single ASSR testing on October 7, 2009.
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