RESUMEN
Two female harbor seals were exposed for 60 min to a continuous one-sixth-octave noise band centered at 32 kHz at sound pressure levels of 92 to 152 dB re 1 µPa, resulting in sound exposure levels (SELs) of 128 to 188 dB re 1 µPa2s. This was part of a larger project determining frequency-dependent susceptibility to temporary threshold shift (TTS) in harbor seals over their entire hearing range. After exposure, TTSs were quantified at 32, 45, and 63 kHz with a psychoacoustic technique. At 32 kHz, only small TTSs (up to 5.9 dB) were measured 1-4 min (TTS1-4) after exposure, and recovery was within 1 h. The higher the SEL, the higher the TTS induced at 45 kHz. Below â¼176 dB re 1 µPa2s, the maximum TTS1-4 was at 32 kHz; above â¼176 dB re 1 µPa2s, the maximum TTS1-4 (up to 33.8 dB) was at 45 kHz. During one particular session, a seal was inadvertently exposed to an SEL of â¼191 dB re 1 µPa2s and at 45 kHz, her TTS1-4 was >45 dB; her hearing recovered over 4 days. Harbor seals appear to be equally susceptible to TTS caused by sounds in the 2.5-32 kHz range.
RESUMEN
As part of a series of studies to determine frequency-dependent susceptibility to temporary hearing threshold shifts (TTS), two female harbor seals (F01 and F02) were exposed for 60 min to a one-sixth-octave noise band centered at 40 kHz at mean sound pressure levels ranging from 126 to 153 dB re 1 µPa [mean received sound exposure level (SEL) range: 162-189 dB re 1 µPa2s]. TTSs were quantified at 40, 50, and 63 kHz within 1-4 min of the exposure for F02 and within 12-16 min of the exposure for F01. In F02, significant TTS1-4 (1-4 min post exposure) occurred at 40 kHz with SELs of ≥183 dB re 1 µPa2s and at 50 kHz with SELs of ≥174 dB re 1 µPa2s. At 63 kHz, TTS1-4 occurred with SELs ≥186 dB re 1 µPa2s. In F01, significant TTS12-16 (12-16 min post exposure) occurred only at 50 kHz with SELs of ≥177 dB re 1 µPa2s. The highest TTSs (27.5 dB in F02, 29.8 dB in F01) occurred at 50 kHz, one-third of an octave above the fatiguing sound's center frequency (SEL = 189 dB re 1 µPa2s); recovery took 2 days in F02 and 4 days in F01. In most other cases, recovery was within 1 h. The seals have a similar susceptibility to TTS from 4 to 40 kHz.
RESUMEN
This study concludes a larger project on the frequency-dependent susceptibility to noise-induced temporary hearing threshold shift (TTS) in harbor seals (Phoca vitulina). Here, two seals were exposed to one-sixth-octave noise bands (NBs) centered at 0.5, 1, and 2 kHz at several sound exposure levels (SELs, in dB re 1 µPa2s). TTSs were quantified at the center frequency of each NB, half an octave above, and one octave above, at the earliest within 1-4 min after exposure. Generally, elicited TTSs were low, and the highest TTS1-4 occurred at half an octave above the center frequency of the fatiguing sound: after exposure to the 0.5-kHz NB at 210 dB SEL, the TTS1-4 at 0.71 kHz was 2.3 dB; after exposure to the 1-kHz NB at 207 dB SEL, the TTS1-4 at 1.4 kHz was 6.1 dB; and after exposure to the 2-kHz NB at 215 dB SEL, TTS1-4 at 2.8 kHz was 7.9 dB. Hearing always recovered within 60 min, and susceptibility to TTS was similar in both seals. The results show that, for the studied frequency range, the lower the center frequency of the fatiguing sound, the higher the SEL required to cause the same TTS.
RESUMEN
Temporary hearing threshold shifts (TTSs) were investigated in two adult female harbor seals after exposure for 60 min to a continuous one-sixth-octave noise band centered at 16 kHz (the fatiguing sound) at sound pressure levels of 128-149 dB re 1 µPa, resulting in sound exposure levels (SELs) of 164-185 dB re 1 µPa2s. TTSs were quantified at the center frequency of the fatiguing sound (16 kHz) and at half an octave above that frequency (22.4 kHz) by means of a psychoacoustic hearing test method. Susceptibility to TTS was similar in both animals when measured 8-12 and 12-16 min after cessation of the fatiguing sound. TTS increased with increasing SEL at both frequencies, but above an SEL of 174 dB re 1 µPa2s, TTS was greater at 22.4 kHz than at 16 kHz for the same SELs. Recovery was rapid: the greatest TTS, measured at 22.4 kHz 1-4 min after cessation of the sound, was 17 dB, but dropped to 3 dB in 1 h, and hearing recovered fully within 2 h. The affected hearing frequency should be considered when estimating ecological impacts of anthropogenic sound on seals. Between 2.5 and 16 kHz the species appears equally susceptible to TTS.
RESUMEN
Loudness perception can be studied based on the assumption that sounds of equal loudness elicit equal reaction time (RT; or "response latency"). We measured the underwater RTs of a harbor porpoise to narrowband frequency-modulated sounds and constructed six equal-latency contours. The contours paralleled the audiogram at low sensation levels (high RTs). At high-sensation levels, contours flattened between 0.5 and 31.5 kHz but dropped substantially (RTs shortened) beyond those frequencies. This study suggests that equal-latency-based frequency weighting can emulate noise perception in porpoises for low and middle frequencies but that the RT-loudness correlation is relatively weak for very high frequencies.
Asunto(s)
Phocoena/fisiología , Tiempo de Reacción/fisiología , Agua de Mar , Sonido , AnimalesRESUMEN
Loudness perception by human infants and animals can be studied under the assumption that sounds of equal loudness elicit equal reaction times (RTs). Simple RTs of a harbour porpoise to narrowband frequency-modulated signals were measured using a behavioural method and an RT sensor based on infrared light. Equal latency contours, which connect equal RTs across frequencies, for reference values of 150-200 ms (10 ms intervals) were derived from median RTs to 1 s signals with sound pressure levels (SPLs) of 59-168 dB re. 1 µPa and centre frequencies of 0.5, 1, 2, 4, 16, 31.5, 63, 80 and 125 kHz. The higher the signal level was above the hearing threshold of the harbour porpoise, the quicker the animal responded to the stimulus (median RT 98-522 ms). Equal latency contours roughly paralleled the hearing threshold at relatively low sensation levels (higher RTs). The difference in shape between the hearing threshold and the equal latency contours was more pronounced at higher levels (lower RTs); a flattening of the contours occurred for frequencies below 63 kHz. Relationships of the equal latency contour levels with the hearing threshold were used to create smoothed functions assumed to be representative of equal loudness contours. Auditory weighting functions were derived from these smoothed functions that may be used to predict perceived levels and correlated noise effects in the harbour porpoise, at least until actual equal loudness contours become available.