In the sense of hearing, sound waves are transmitted to the fluid-filled cochlea, where they are converted to neural messages and sent to the brain. Together, the place and frequency theories explain how we hear both high-pitched and low-pitched sounds. The mechanical system that enables us to hear is fairly sensitive and easily subjected to damage, causing hearing loss.
The Stimulus Input: Sound Waves and The Ear
‰ Exercise: Auditory Demonstrations on CD
‰ Lecture: Recognizing Our Own Voice
‰ PsychSim 5: The Auditory System
19-1. Describe the auditory process, including the stimulus input and the structure and function of the ear.
Audition, or hearing, is highly adaptive. The pressure waves we experience as sound vary in amplitude and frequency and correspondingly in perceived loudness and pitch. Decibels are the measuring unit for sound energy.
The visible outer ear channels the sound waves through the auditory canal to the eardrum, a tight membrane that vibrates with the waves. Transmitted via the bones of the middle ear (the hammer, anvil, and stirrup) to the fluid-filled cochlea in the inner ear, these vibrations cause the oval window to vibrate, causing ripples in the basilar membrane, which bends the hair cells that line its surface. This movement triggers neural messages to be sent (via the thalamus) to the temporal lobe’s auditory cortex. Damage to the hair cells accounts for most hearing loss.
‰ Exercise: Locating Sounds
19-2. Contrast place and frequency theories, and describe how we pinpoint sounds.
Place theory presumes that we hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane. Thus, the brain can determine a sound’s pitch by recognizing the place on the membrane from which it receives neural signals.
Frequency theory states that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch. The volley principle explains hearing sounds with frequencies above 1000 waves per second.
Place theory best explains how we sense high-pitched sounds, and frequency theory best explains how we sense low-pitched sounds. Some combination of the two theories explains sounds in between.
Sound waves strike one ear sooner and more intensely than the other ear. We localize sounds by detecting the minute differences in the intensity and timing of the sounds received by each ear.
Hearing Loss and Deaf Culture
‰ Lectures: Hearing Loss; A Quiet World—Living With Hearing Loss
19-3. Contrast the two types of hearing loss.
Problems with the mechanical system that conducts sound waves to the cochlea cause conduction hearing loss. If the eardrum is punctured or if the tiny bones of the middle ear lose their ability to vibrate, the ear’s ability to conduct vibrations diminishes. Damage to the cochlea’s hair cell receptors or their associated nerves can cause the more common sensorineural hearing loss. Once destroyed, these tissues remain dead. Disease, biological changes linked with aging, or prolonged exposure to ear-splitting noise or music may cause sensorineural hearing loss.
Those who live with hearing loss face social challenges. Cochlear implants are wired into various sites on the auditory nerve, allowing them to transmit electrical impulses to the brain. They help children to become proficient in oral communication. The latest cochlear implants also can help restore hearing for most adults. Deaf culture advocates object to using the implants on children who were deaf before developing language. They note that deafness is not a disability because sign is a complete language. Some also argue that sensory compensation, which enhances other senses, gives deaf people advantages that the hearing do not have.