Introduction

The human inner ear is consisted of two separate organs; the cochlea and vestibule. The cochlea is an organ of hearing, the vestibule is responsible for maintaining the body's balance in linear and angular accelerations [1, 2]. The SVSS in human has been confirmed by invention of the cVEMPs [3,4,5,6,7,8,9]. It is generated during the stimulation of the sternocleidomastoid muscle with intense low frequency sounds [3, 10, 11]. The saccule has highest sound sensitivity between vestibular organs [12,13,14].

Pathologies that involve the inner ear cochlea, also cause damage to the saccule. Then, the most susceptibility of the vestibular organs to impairment is related to the saccule, in cases of sensorineural hearing loss [15, 16], Meniere's disease [17], sudden sensorineural hearing loss [18, 19], auditory-neuropathy [20], noise induced hearing loss [21], destructive effects of musical sounds [22], aging [23], ototoxic drugs [24], and covid-19 [25]. Also, continuous loudly singing, which lasts longer than duration time of the stapedius reflex of the middle ear can cause saccular damage [26]. In addition, the recovery of the patients with acute low-frequency sensorineural hearing loss and saccular damage is weaker than similar cases with normal saccular function [27].

The most important reason for saccular susceptibility to impairment is the proximity of the saccule to the cochlea through the Reunion duct [2], which connects the lower part of the saccule to the cochlear duct near its vestibular extremity [1].

The aim of this study is to investigate central representation of vestibular system sensitivity to sound. In order to retrieve original documents that were published between 2000 and 2022, information sources about SVSS in human were studied, such as Science Citation Index, Web of Science, PubMed, PubMed/Medline, Scopus, Springer, Pearson, Google Scholar. First, 89 documents were found, and finally 58 papers that were related to the title of this study were considered. The criterion for selecting articles was their overlap with the purpose of this work and gain access to the full text of the sources. The SVSS in animal literatures was not included.

Results

A summary of the conclusion section of the published articles on sensitivity of vestibular system to sounds in the years 2000 to 2023 is presented in Table 1.

Table 1 A summary of the conclusion section of the published articles on sensitivity of vestibular system to sounds
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Fig. 1
figure 1

Pure tone audiogram of the right ear a person with profound sensorineural hearing loss and false air-bone gaps (ABG) in 250-500HZ, and normal cVEMPs [47]

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Fig. 2
figure 2

Pure tone audiogram of the left ear a person with profound sensorineural hearing loss and abnormal cVEMPs, bone-conducted hearing thresholds were not presence [47]

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Discussion

Based on the findings reported in the results section of this research, the human vestibular system is sound sensitive and sends signals to the neural centers of the brainstem and the brain. Now, this question is raised: Are the neural information from the vestibular system useful in the neural processing? To answer this question, it is necessary to take a brief look at how to learn new words.

Learning the first language for every native listener is a natural part of that person's daily life, which is formed based on the relationship he/she has with the world around him. The first language of a child is part of that child's personal, social and cultural identity, it brings about the reflection and learning of effective social patterns of acting and speaking [48]. To perception the world, contribution of all senses is necessary. Learning the first words is not only based on the hearing and other senses participate. The auditory object is a three-dimensional imaging in people's minds, when they hear a word. The words expressed by a speaker create different auditory Objects in people's minds. For example, upon hearing the word "flower", different auditory objects of flower may be represented for people; a flower in a glass, a flower in a garden, a faded flower, a flower in a bride's hand or a flower on a tombstone. Each of these auditory objects has its own color, shape, aroma and characteristics. Then for a native listener, each spoken word is equivalent to an auditory object. For the formation of the auditory objects, all senses and whole areas of the brain contribute [49].

Speech-in-noise perception is also done with the participation of all areas of the brain. The neural centers for speech perception are various and temporal lobe is influenced by several sensory processings and mechanisms, the auditory brain is not actually monosensory and had multi-modal processing [38, 50, 51].

The vision also plays a guiding role in the formation and maturation of auditory responses. If the visual signals are damaged during childhood, the auditory representation in the superior colliculus is impaired due to the disturbance in the normal development. Vision problems due to surgery or head trauma can disturb the auditory spatial balance in the nucleus of the superior colliculus [52].

The inferior frontal gyrus improves people’s accuracy in repeating unfamiliar foreign speech sounds, and matches perceived speech to produced speech [49]. Mirror-neuron brain areas, which have no role in interpretation of high-level activities and are involved in low-level processing have a precise and essential role in speech-in-noise perception [53].

The insula in the left cortex is exactly motivated when main frequency of human voices transport lexical information to a native listener, whereas the insula of the right cortex is activated once main frequency of human voices do not provide lexical information [48]. The cingulo-opercular system is involved in central-peripheral processing of attention and control [49]. Therefore, the neural signals from the vestibular system project to various areas of the brain and participate to other senses for formation the auditory Objects.

The SVSS is in the range of the fundamental frequency of the human voice [36], which differs between men = 100HZ, women = 200HZ, and infants = up to 400HZ [54]. Considering that the saccule is close to the larynx and is also connected to the cochlea [2], the afferent nerve fibers of the saccule are stimulated during self-voice production [34, 38], and the person ossifies his own voice through feedback control or bone-conducted pathway [38].

Saccular nerve fibers spirit to the brainstem. The brainstem is also sensitive to low-frequency sounds and participates in detection the pitch of speech and the melody of music. The brainstem encodes the first formant of speech (the lowest frequency or the strongest harmonic of the speaker's voice), which is necessary for the perception of vowels [51, 54]. Therefore, the acoustical information of the vestibular system that goes to the brainstem may be effective in detection beats and pitch [30, 33].

The SVSS can be motivated when people participate in group activities in noisy competing situations, e.g. singing poetry together, chanting in the crowd, shouting in the group, cheering on their favorite team in sports activities, performing military parades, and similar cases [7, 9, 38, 39, 55,56,57,58].

The limbic receives inputs from vestibular afferent nerve fibers and regulates emotions, such as anger, joy, hate, sadness [28]. The limbic is also connected to musculo-skeletal systems [8, 9]. Then, intense low-frequency sounds stimulate the saccule, the limbic, the musculo-skeletal systems [9] and generate the desire to perform the harmonic movements, in the form of pacing, marching, clapping or chest beating [28, 31, 41].

Conclusion

For the formation of the auditory objects, all senses and whole areas of the brain contribute. Like other senses, central representation of vestibular system sensitivity to sound are also involved in the formation of auditory objects.