Chapter 9 Study Questions
The Function of Hearing
What Is Sound?
1. Describe the two basic qualities of sound: frequency and amplitude.
Answer: Frequency is the number of times per second that a pattern of pressure change repeats. Amplitude is the magnitude of displacement (increase or decrease) of a sound pressure wave.
2. How is amplitude associated with loudness?
Answer: Loudness is the psychological aspect of sound related to perceived intensity or magnitude, while amplitude is the physical magnitude of displacement of a sound pressure wave. The more amplitude a sound wave has, the louder it will sound.
3. What is a sine wave and why is it important in studying auditory perception?
Answer: A sine wave is a waveform for which variation as a function of time is a sine function. It is important in studying auditory perception because all sounds are made of sine waves, usually a combination of several various types. Understanding them is important to understanding auditory perception.
4. Describe the concept of timbre.
Answer: Timbre is the psychological sensation by which a listener can judge that two sounds that have the same loudness and pitch are dissimilar (e.g., a trumpet and a piano both playing the same note still sound different from each other). Timbre quality is conveyed by harmonics and other high frequencies.
Basic Structure of the Mammalian Auditory System
5. What are the roles of the ear canal?
Answer: The ear canal is responsible for: 1) Conducting sound vibrations from the pinna to the tympanic membrane; and 2) Preventing damage to the tympanic membrane.
6. Describe the three tiny bones in the middle ear.
Answer: The three tiny bones in the middle ear are the ossicles: the malleus, the incus, and the stapes. They amplify the sound arriving at the tympanic membrane before it is transmitted to the oval window. The malleus receives vibration from the tympanic membrane and is attached to the incus. The incus connects between the malleus and the stapes. The stapes presses against the oval window of the cochlea on the other end.
7. Why can't the acoustic reflex help protect the ear from abrupt loud sounds, such as gun fire?
Answer: The acoustic reflex is a reflex that protects the ear from intense sounds by the contraction of the stapedius and tensor tympani muscles. However, this reflex follows the onset of loud sounds by about 200 ms, so it cannot protect against abrupt loud sounds.
8. What is the function of the cochlea?
Answer: The cochlea is a spiral structure of the inner ear containing the organ of Corti, which is responsible for transducing the mechanical movement of sound vibration into neural activity.
9. Describe how the release of neurotransmitters results from the deflection of stereocilia (hair cells).
Answer: When vibration causes a displacement along the cochlear partition, the tectorial membrane and hair cells move in opposite directions (shear) and the deflection of stereocilia in this action results in the release of neurotransmitters.
10. How is place code related to tuning?
Answer: Place code is the tuning of different parts of the cochlea to different frequencies, in which information about the particular frequency of an incoming sound wave is coded by the place along the cochlear partition with the greatest mechanical displacement due to its resonance with that frequency.
11. How are inner hair cells different from outer hair cells?
Answer: Inner hair cells convey almost all the information about sound waves to the brain. Outer hair cells, on the other hand, receive information from the brain to the cochlea as part of a feedback system. Outer hair cells help to stiffen parts of the cochlear partition and improve the sensitivity and frequency selectivity of the inner hair cells.
12. What is the threshold tuning curve?
Answer: The threshold tuning curve is a map plotting the thresholds of a neuron or fiber in response to sine waves with varying frequencies, at the lowest intensity that will give rise to a response.
13. What happens during two-tone suppression?
Answer: Two-tone suppression is a decrease in the firing rate of one auditory nerve fiber to a tone, when a second tone is presented at the same time.
14. What does an isointensity curve show us?
Answer: An isointensity curve is a map that plots the firing rates of an auditory nerve fiber against varying frequencies and intensities.
15. What is rate saturation?
Answer: Rate saturation is the point at which a nerve fiber is firing as rapidly as possible and further stimulation is incapable of increasing the firing rate.
16. Why does phase locking occur?
Answer: Phase locking may occur because AN fibers fire when the sterocilia of hair cells move in one direction (e.g., as the basilar membrane moves up toward the tectorial membrane), but they do not fire when the stereocilia move in the other direction.
17. Describe the volley principle.
Answer: The volley principle is the idea that multiple neurons can provide a temporal code for frequency if each neuron fires at a distinct point in the period of a sound wave but does not fire on every period.
18. What kind of organization exists in the primary auditory cortex (A1)?
Answer: The primary auditory cortex is organized in a tonotopic fashion. This is an arrangement in which neurons that respond to different frequencies are organized anatomically in order of frequency.
Basic Operating Characteristics of the Auditory System
19. What is psychoacoustics?
Answer: Psychoacoustics is the study of the psychological correlates of the physical dimensions of acoustics; a branch of psychophysics.
20. What is the audibility threshold?
Answer: It is a map of just barely audible tones of varying frequencies.
21. What is white noise and when is it used?
Answer: White noise consists of all audible frequencies in equal amounts. White noise in hearing is analogous to white light in vision, for which all wavelengths are present. It is used in masking experiments investigating frequency selectivity.
Hearing Loss
22. Describe two kinds of hearing loss.
Answer: One is conductive hearing loss, which is caused by problems with the bones of the middle ear and can be remedied by surgery. The other is otitis media, which is the inflammation of the middle ear, commonly in children as a result of infection.
23. How does a cochlear implant work?
Answer: A cochlear implant consists of a flexible array of electrodes that are inserted into the cochlea through the round window as far as possible towards the apex of the cochlea. The electrode array connects to a small receiver beneath the scalp, which receives signals from a small microphone and transmitter placed over the receiver on the outside of the head. Sounds captured by the microphone are transmitted to the electrode array, which stimulates cells in the cochlea, allowing the person to hear.