Abstract
This chapter ponders answers to several questions asked by music listeners not having direct experience with the sounds: How does the brain perceive sounds? How does the harmonic series dominate music? What are consonances and dissonances? Why do octaves sound nearly the same? What is perfect pitch? How do you have a brilliant child by boosting its sensory perception in the perinatal period?
TopHow The Brain Perceives Sounds
No sound ever reaches the brain. How can that be since that we know very well what we are listening to? You may think that there are little rubber tubes connecting the ear canals to the brain, but it is not so. The inner ear converts sounds into neural impulses that travel up the auditory ganglion or nerve bundle to the brain. There are many nerves in this bundle. Some who have done dissections have suggested that there are between 30,000 to 50,000 nerves in the auditory nerve system. Thus, the brain receives all the information it needs to understand the sounds that are arriving at the ear. But how does it know about subjective aspects of sounds? How does it know how to respond to sounds, which sounds are indicative of safe environments and which ones are dangerous and scary. Which ones are melancholy, happy, sad, terrifying? How does the brain know what an English horn sounds like since it never receives that sound but only a description of it.
The Temporal Theory
The temporal theory has to do with the way the cochlea (the inner ear) works. Specialists have worked on this for many years and now say that we perceive both the frequency and the period of a vibration. The basilar membrane perceives the frequency by the Fourier analysis of an incoming tone, while the period is perceived in the cochlear nucleus by a temporal process that works separately for each bundle of auditory fibers connected to a single inner hair cell. The temporal process involves the autocorrelation of each single frequency with a delayed copy of itself. The big innovation here is that temporal theory is applied separately to each individual frequency rather than to the entire sound wave. This means that there are as many temporal processors as there are inner hair cells.
Key Terms in this Chapter
Sound Waves: Sinusoidal waves characterized by their frequency, amplitude, intensity (sound pressure), speed, and direction. Pairs of sound waves may reveal additive and subtractive interference.
Pitch: A sound quality describing the highness or lowness of a tone, defined by the rate of vibration that produces it.
Tonotopic: Organization means the arrangement of spaces in auditory cortex where sounds of different frequency are processed in the brain. Tones close to each other frequency are represented in topologically near regions in the brain.
Acoustic Waves: Longitudinal waves with the same direction of vibration as the direction of their traveling in a medium such as air or water. Linear mixing of acoustic waves results in forming periodicity pitches of the resultant tones