Chapter 10 Study Questions
Sound Localization
1. Describe the concept of interaural time difference and its importance.
Answer: Interaural time difference is the difference in time between a sound arriving at one ear versus the other. It is an important cue for localizing sound.
2. How do the medial superior olive structures help in sound localization?
Answer: The medial superior olive structures serve as relay stations in the brain stem where inputs from both ears contribute to the detection of the interaural time differences, which in turn are critical for localizing sound.
3. What is the interaural level difference?
Answer: The interaural level difference is the difference in level (intensity) between a sound arriving at one ear versus the other. It helps with sound localization.
4. What happens to sound information traveling to the ears after only a single synapse in the cochlear nucleus?
Answer: The information from each ear travels to both the medial superior olive and the lateral superior olive on each side of the brain stem.
5. Why is the cone of confusion confusing?
Answer: The cone of confusion is the region of positions in space where all sounds produce the same time and level (intensity) differences. In such a situation it is difficult to localize sound, which is confusing to the listener.
6. Provide one reason why cones of confusion are not major practical problems for the auditory system.
Answer: One such reason is that time and intensity differences are not the only cues for hearing the location of sound sources. The shape of the pinna, for instance, also helps with sound localization. It “funnels” sound energy into the ear canal, and does this more efficiently for some sound frequencies than for others. In addition, the intensity of each frequency varies slightly according to the direction of the sound, and this variation provides the listener with another localization cue.
7. What does the directional transfer function describe?
Answer: This function describes how the pinna, ear canal, head, and torso change the intensity of sounds with different frequencies that arrive at each ear from various locations in space.
8. What does the inverse-square law state?
Answer: The inverse-square law states that as distance from a source increases, intensity decreases faster such that the decrease in intensity is the square of the distance.
9. How do the relative amounts of direct versus reverberant energy provide a cue for auditory distance?
Answer: The relative amounts of direct versus reverberant energy provide a cue for auditory distance because when a sound source is close to the listener, most of the energy reaching the ear is direct, whereas reverberant energy provides a greater proportion of the total when the sound source is farther away.
Complex Sounds
10. What is a fundamental frequency?
Answer: A fundamental frequency is the lowest-frequency component of a complex periodic sound.
11. Describe the phenomenon of the “missing fundamental.”
Answer: The “missing fundamental” is the phenomenon in which listeners will still hear the pitch of a missing fundamental frequency of a harmonic sound even if it is not present in the actual sound wave.
12. What is timbre?
Answer: Timbre is the psychological sensation by which a listener can judge that two sounds having the same loudness and pitch are in fact different. Timbre quality is conveyed by harmonics and other high frequencies.
13. What is the difference between the attack and the decay of a sound?
Answer: The attack of a sound is the part during which amplitude increases. The decay of a sound is the part during which the amplitude decreases.
Auditory Scene Analysis
14. How does source segregation help us to distinguish various sounds in our environment?
Answer: Source segregation is the processing of an auditory scene consisting of multiple sound sources into separate sound images. This process helps us ultimately distinguish between the different sound sources in our environment.
15. Describe the idea of auditory stream segregation.
Answer: Auditory stream segregation is the perceptual organization of a complex acoustic signal into separate auditory events for which each stream is heard as a separate event.
16. What happens when a sequence of notes that have increasing and decreasing frequencies is presented and tones deviate from the rising/falling pattern?
Answer: These deviating tones are heard to “pop out” of the sequence because they do not share the same timbre as the rest of the notes in the group.
Continuity and Restoration Effects
17. How is “hearing through” an interruption consistent with the Gestalt principle of good continuation?
Answer: “Hearing through” an interruption is consistent with the Gestalt principle of good continuation because in this case, the listener is able to “make up” for the missing sound piece due to the interruption. The Gestalt principle of good continuation also states that the perceiver will make up for a lost piece by filling in for it.
18. Explain the idea of restoration of complex sounds.
Answer: Restoration of complex sounds can occur when listening to speech or music, which are complex sounds. The missing notes or segments of speech are filled in by the listener, and the whole piece is thus restored.
Auditory Attention
19. What is the acoustic startle reflex?
Answer: It is a very rapid motor response to a sudden sound. The startle response is more likely to occur when the person is already tense and anxious. A sudden noise will cause the person to jump, which is the startle reflex.
20. What is inattentional deafness?
Answer: Similar to inattentional blindness, when somebody is concentrating on one auditory stream they might miss an otherwise obvious event that occurs in the other auditory stream.