Sound Recognition: Interpretation by the Brain and the Potential for Illusion

The phenomenon of humans hearing sounds is a process where physical vibrations called sound waves are transmitted to the brain through the auditory organs, converted into electrical signals within the brain, and finally recognized as "sound." However, this recognition is not merely a direct reflection of objective physical phenomena, but rather a result of interpretation and reconstruction by the brain, suggesting the possibility of it being a kind of illusion. Below, we will elaborate on this complex process by dividing it into three stages, explaining the brain's role and the potential for illusion at each stage.

Sound Reception and Conversion: The Role of Auditory Organs and Brainstem

Sound, in the form of air vibrations known as sound waves, travels through the ear canal and reaches the eardrum. The vibrations of the eardrum are amplified by the ossicles in the middle ear. These amplified vibrations are transmitted to the cochlea in the inner ear, where hair cells convert the vibrations into electrical signals. These electrical signals are transmitted to the brainstem via the auditory nerve, where basic sound features (frequency, intensity, timing information, etc.) are processed.

At this stage, sound is merely converted from physical vibrations into electrical signals, and recognition as "sound" has not yet occurred. However, complex processes are carried out to accurately capture the physical properties of sound, such as frequency resolution in the cochlea and sound source localization in the brainstem.

Sound Perception and Recognition: The Role of the Cerebral Cortex

The electrical signals processed in the brainstem are sent to the auditory cortex in the cerebral cortex, where higher-order sound features such as pitch, timbre, rhythm, and melody are analyzed. Furthermore, through collaboration with language areas and memory-related areas surrounding the auditory cortex, meaning and emotional value are assigned to the sound, ultimately leading to its recognition as "sound."

At this stage, the brain interprets and assigns meaning to sounds based on past experiences and knowledge. For example, the same sound can be recognized as meaningful words if it's linguistic or as a beautiful melody if it's music. In this way, sound recognition involves collaboration with various information processing areas in the brain, making it highly subjective and prone to illusions.

Auditory Illusions: Limitations and Misinterpretations in Brain Processing

The brain's recognition of sound does not always accurately reflect objective physical phenomena. For instance, the perceived pitch of a pure tone with the same frequency can change depending on the frequencies of sounds presented before and after it (context effect). Additionally, auditory hallucinations, where non-existent sounds are heard, and hyperacusis, where one is overly sensitive to specific sounds, are also considered types of illusions arising from errors in brain processing.

Furthermore, sound recognition is influenced by individual experiences and cultural backgrounds. For example, music considered beautiful in one culture might be perceived as unpleasant in another. In this way, sound recognition is significantly influenced not only by the biological characteristics of the brain but also by individual experiences and cultural backgrounds, suggesting that the very concept of objective "sound" itself might be a kind of illusion.

Conclusion: Sound Recognition is a Result of Interpretation and Reconstruction by the Brain

As described above, the phenomenon of humans hearing sounds is a process where physical vibrations called sound waves are transmitted to the brain through the auditory organs, converted into electrical signals within the brain, and finally recognized as "sound." However, this recognition is not merely a direct reflection of objective physical phenomena, but rather a result of interpretation and reconstruction by the brain, suggesting the possibility of it being a kind of illusion.

Sound recognition occurs through multiple stages: physical conversion in the auditory organs, basic processing in the brainstem, and higher-order analysis and interpretation in the cerebral cortex. By understanding the brain's role and limitations at each stage, we can gain a deeper understanding of how humans recognize sounds and what kind of illusions can arise.

R E - C E R E B R O ： 脳神経科学-音の認識