(Left panel) Sample psychometric function for the sea lion. Percentage of correct detection is plotted as a function of sound pressure level (SPL) for a 100 ms tone at 2.5 kHz. (Right panel) Probit transformed values of the correct detection rates as function of SPL. The solid line is the least squares fit of the data (dotted lines: 5%–95% confidence limits). The threshold for this stimulus, measured at 50% correct detection level (which corresponds to a probit value of 5) is 35.5 dB as indicated by the arrows.
Aerial hearing thresholds for the California sea lion (Zalophus). Thresholds are plotted as a function of signal duration for each the frequencies tested (2.5, 5, and 10 kHz). The curves fitted and time constants (τ) shown are based on an exponential model [Eq. (2)]; see the text for details.
Time constants,τ, based on Eq. (1) as a function of mid-range test frequency (1–10 kHz) for selected mammal species: California sea lion in air (current study), harbor seal under water (Kastelein et al., 2010), bottlenose dolphin under water (Tursiops truncatus; Johnson, 1968 from Fay, 1988), and human (Watson and Gengel, 1969) and domestic cat (Felis catus; Costalupes, 1983) in air.
Aerial hearing thresholds (dB SPL re: 20 μPa, ±SE) of a California sea lion to pure-tone stimuli are shown at nine signal durations for each of three signal frequencies; the testing order and false alarm rate (percentage and number of false alarms out of total number of catch trials pooled across experimental sessions) are also provided.
Parameter estimates based on two exponential models [Eqs. (1) and (2)] for aerial hearing thresholds of a California sea lion to pure-tone signals, shown as a function of signal duration.a
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