Recorded vibrations of gray whale skulls to study how vibrations in the skull are amplified in the bony hearing complex to facilitate low frequency hearing

Mysticete whales have a bony ear complex (tympanoperiotic complex, TPC)
that supports highly sensitive hearing at low frequencies. Components of
the mysticete TPC include the tympanic bulla, which is suspended from the
skull by two thin, flexible bones (pedicles), and the periotic bone, which
encases the cochlea and is embedded in the skull. Between the bulla and
the periotic are the ossicular chain (middle ear bones) that excite the
cochlear fluid and hence the sensory organs of hearing. We conducted
experiments to measure the vibrational dynamics between the tympanic
bullae and the base of the skull in both a juvenile and an adult gray
whale. For the juvenile, assessments were performed on three versions of
the skull: a plastic replica produced by 3D printing from CT scans of the
original specimen, the original skull after much of the soft tissue had
been removed by dissection, and the denuded skull after hydrogen peroxide
was used to erode soft tissues within the cavities of the skull. We
excited vibrations in the juvenile skull underwater by projecting sound in
a test pool, ranging from 170 - 1000 Hz. Additionally, we measured in-air
vibrations of the plastic skull, the denuded skull, and the adult skull
using a mechanical shaker to drive vibrations anteroposteriorly
(rostrum-to-tail) from 150 - 1000 Hz. This dataset includes recordings
from 7 uniaxial accelerometers during each of the experiments. Frequency
response functions (vibration velocity amplitude vs. frequency)
consistently revealed amplification of vibrations at the tympanic bullae
compared to the base of the skull, demonstrating a mechanism by which
low-frequency sound is transferred from the environment into the inner
ear.

须鲸类（Mysticete whales）具备骨性耳复合体——鼓围耳骨复合体（tympanoperiotic complex, TPC），该结构可支持其实现低频声波的高灵敏听觉。须鲸类鼓围耳骨复合体的组成构件包括：通过两根纤细柔韧的骨柄（pedicles）悬挂于颅骨的鼓膜泡（tympanic bulla），以及包裹耳蜗（cochlea）并嵌合于颅骨内的围耳骨（periotic bone）。鼓膜泡与围耳骨之间存在听小骨链（ossicular chain，中耳骨），该结构可激发耳蜗液，进而激活听觉感官器官。
本研究开展实验，旨在测量幼年与成年灰鲸（gray whale）的鼓膜泡与颅骨基底之间的振动动力学特性。
针对幼年灰鲸样本，我们基于三种颅骨版本开展评估：一是通过对原始标本的CT扫描（CT scans）数据进行3D打印（3D printing）制作的塑料复制品；二是经解剖（dissection）去除大部分软组织后的原始颅骨；三是使用过氧化氢（hydrogen peroxide）腐蚀颅骨腔隙内残留软组织后的脱软组织颅骨。
我们在试验水池中投射170~1000 Hz的声波，对幼年灰鲸颅骨施加水下振动激励。此外，我们采用机械振动台沿前后轴方向（吻部至尾部，rostrum-to-tail）驱动振动，频率范围为150~1000 Hz，分别对塑料复制品颅骨、脱软组织颅骨以及成年灰鲸颅骨开展了空气中的振动测量。
本数据集包含了所有实验过程中7台单轴加速度计（uniaxial accelerometers）采集的记录数据。频率响应函数（frequency response functions，振动速度幅值vibration velocity amplitude随频率变化曲线）一致显示：相较于颅骨基底，鼓膜泡处的振动存在显著放大，这揭示了低频声波从环境传递至内耳的潜在机制。