Procedure For Determining Audiograms In Toothed Whales (Odontocetes)

Procedure For Determining Audiograms In Toothed Whales ANSI/ASA S3 SC.1 2018
A Sperm Whale dives off the coast of New Zealand

Communication isn’t unique to human society, nor is it confined to the terrestrial world. Whales, as highly-intelligent mammals bound to the sea—and whales are mammals, despite a long-held misconception to the alternative and the infamous 1818 court case that ruled cetaceans to be fish—use an assortment of noises to communicate with each other.

All whales are social animals, and odontocetes, or “toothed whales,” are no exception. Using sounds, whales interact with one another or their surroundings. Through the use of clicks, cetaceans identify their physical surroundings, identifying shapes by assessing the way sound waves bounce off objects and return to them. They also make use of whistles and pulsed calls during social activities and utilize their tails and fins to make loud slapping noises for communication.

All these observed patterns are, of course, drastically different than the thousands of languages and nearly infinite nonverbal cues conveyed by human beings in our social interactions, so humans are left trying to figure out what each nuanced whale noise means and the potential impact of anthropogenic ocean sound on cetacean life. As alluded to in ANSI/ASA S3/SC1.6-2018: Procedure For Determining Audiograms In Toothed Whales Through Evoked Potential Methods, the use of auditory evoked potential (AEP) methods to obtain audiograms from toothed whales has become increasingly common. Of these approaches, the use of sinusoidally amplitude-modulated (SAM) tones is the most typical to elicit the auditory steady-state response (ASSR), or the “evoked response to a periodic stimulus resulting in a waveform with the same periodicity as the stimulus modulation envelope or repetition rate.”

However, as this method has accelerated in popularity, varied ways of calibrating test stimuli and calculating hearing thresholds with varying estimates for the same species and frequencies tested have led to a considerable amount of confusion in the communities that seek to predict, mitigate, and regulate the potential impact of sound on marine communities.

Comprehending the nature of these tones is instrumental in understanding whales and the impact underwater sounds can have on them, as odontocetes account for about 90% of all cetaceans. Furthermore, whales have long been impacted by human influence. For example, the sperm whale, a prominent toothed whale, contains the largest brain of any creature that has ever lived on Earth. However, its head also contains spermaceti, so the intelligent animal was long hunted for this resource and whale oil, becoming renounced for the sinking of the Essex and inevitably serving as the basis for Herman Melville’s Moby Dick.

As such, the acquisition of information regarding marine mammal hearing is relevant to numerous scientists, and the users of this data may include those in academia, regulators, and government and private agencies that need to address the potential impact of human-caused sound on marine mammals. It comes as no coincidence that these groups are also the intended users of the American National Standard ANSI/ASA S3/SC1.6-2018.

Ultimately, the objective of ANSI/ASA S3/SC1.6-2018 is to provide consistent guidelines for collecting audiograms. This data is anticipated for use in interspecies comparisons of hearing abilities, as well as to improve the ability to predict and mitigate the potential impact of underwater sound on odontocetes.

Specifically, ANSI/ASA S3/SC1.6-2018 establishes methods for measuring the ASSR generated by SAM tones and tone-burst trains in odontocetes. This includes instructions for appropriate stimulus waveforms and stimulus calibration. It also sets configurations for electrode placement and stimulus delivery, and it discusses reporting electrophysiological and acoustical noise.

Other than sperm whales, toothed whales include pygmy sperm whales, beaked whales, river-dolphins, belugas and narwhals, dolphins, and porpoises.

ANSI/ASA S3/SC1.6-2018: Procedure For Determining Audiograms In Toothed Whales Through Evoked Potential Methods is available on the ANSI Webstore.

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