These lower brain centers coordinate signals from our two ears, allowing us to locate sounds, and respond to sounds of danger so we can take immediate action even without conscious thought.īut most conscious perceptual processing occurs in the auditory cortex, a part of the brain’s evolved outer layer that lies along the side of the head, in the temporal lobe. The process begins as information from the cochlea travels through the olive and inferior colliculus in the brain stem, then on up through other structures to the thalamus, a kind of central switching station for the senses. It is in the brain that we perceive sounds-become conscious of them and interpret what they mean. Signals from the ear carry the bare sensation of individual components of sound. The “rate theory,” on the other hand, contends that some sounds, perhaps those at the low end of the frequency spectrum, are encoded by the rate of neuron activation: within this range, higher-pitched sounds stimulate neurons to fire more rapidly. This explanation is called “place theory.” Some frequencies of sound may be encoded by which hair cells respond: cells at the base of the cochlea are moved by high-pitched sounds, while those that line the cochlea as it winds toward its apex respond to increasingly lower frequencies. But there is some controversy over just how. The cochlea thus translates sound waves into the language of the brain. This movement opens tiny pores in the hair cells, allowing charged particles (ions) to enter, generating electric impulses that are picked up by nearby filaments of the auditory nerve, which carries them to the brain. The vibration of the ossicles against a window at its base generates waves that ripple through this fluid, pushing against a membrane that is lined with thousands of tiny (about a thousandth of an inch long) hair cells-the receptors of the auditory system. The cochlea is shaped like a spiral snail shell and contains fluid-filled canals. These ossicles, the smallest bones in the body, magnify the motion of the eardrum some twentyfold.Īt their other end, the ossicles transmit their tiny movements to the cochlea, the organ of the inner ear that actually translates the energy of sound waves into nerve signals. In the middle ear, the vibrations are transmitted to three linked bones. Sound waves enter the hearing system through the outer ear, traveling down through the inch-long ear canal to strike the tympanic membrane, or eardrum, and making it vibrate. The sounds we hear represent a richly layered mix of frequencies and amplitudes, faithfully transmitted through a finely engineered apparatus. The loudest we can handle without immediately damaging our hearing (for example, standing 100 feet from a jet at takeoff) carries about a million million times more energy than the barely audible. The diversity of sounds we can hear typically ranges from 20Hz (cycles/second) to 20,000Hz. It turns physical movement into the electrical signals that make up the language of the brain, translating these vibrations into what we experience as the world of sound. Amplitude-how wide the pressure variations-determines volume. Frequency-how many cycles per second-determines the pitch of the sound. Such motions as objects striking or rubbing against each other, air agitated by vocal cords, or gases rushing through a car’s muffler produce cyclical pressure variations in the air: sound waves. Emotional disturbance (e.g.Words of love, or wisdom the timeless murmur of wind in the trees the warning blare of a car horn the sublime harmonies of Mozart-our sense of hearing informs, enriches, and all too often disrupts our lives.Increased or decreased interest in sexual behaviour.Difficulty in recognising faces (Prosopagnosia).Difficulty learning and retaining new information.Difficulty with identification and categorisation of objects.Disturbance with selective attention to what we see and hear.Difficulty in understanding spoken words (Receptive Aphasia).visuo-spatial material and music).ĭamage to the temporal lobes can result in: The non-dominant lobe, which is typically the right temporal lobe, is involved in learning and remembering non-verbal information (e.g. The dominant temporal lobe, which is the left side in most people, is involved in understanding language and learning and remembering verbal information. The temporal lobes are also believed to play an important role in processing affect/emotions, language, and certain aspects of visual perception. They are most commonly associated with processing auditory information and with the encoding of memory. The temporal lobes sit behind the ears and are the second largest lobe.
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