SPHSC 461, Intro to Hearing Science

Spring 2004

Exam 2

 

Define the following terms (5 pt each)

 

  1. threshold

 

The stimulus value that a listener can detect or diswcriminate some arbitrary percent of the time.

 

  1. spectral splatter

 

The spread in the spectrum of a frequency-specific sound into adhjacent frequencies when the sound is turned on or off.

 

  1. phon scale

 

A scale of loudness based on loudness matching on which the loudness of a sound is equal to the level of a 1 kHz tone that sounds equally loud.

 

  1. *psychometric function

 

A function relating performance to stimulus value.

 

True or false? (2 pt each)

 

6.     __T__ The shape of the human audibility curve is largely determined by the external and middle ear.

7.     __T___ The temporal modulation transfer function is a measure of temporal resolution that controls for differences in intensity resolution.

  1. *__T_ Pitch height continues to increase as the frequency of a sound is increased.
  2. __T__ The psychophysical manifestation of the filtering of sound performed by the ear is called the auditory filter.

    3.
  3.  Sketch the human audibility curve. Label axes and indicate some approximate values along the axes. (10 pt)

 

 

 

  1. What is WeberÕs Law? Give one example of a case in hearing in which WeberÕs Law holds. (8  pt)

WeberÕs law states that the just discriminable change in a stimulus is a constant proportion of the stimulus value, ÆS=kS or ÆS/S = k.

 

It holds in: Intensity discrimination of broadband noise, tone in notched noise, very high frequency, mid intensity range; *frequency discrimination if midfrequencies

 

  1. *What is meant by Òvirtual pitchÓ? Describe one theory of how virtual pitch arises. (8 pt)

Virtual pitch refers to the fact that a harmonic complex is perceived to have a pitch corresponding to its fundamental frequency when the fundamental component is missing.

Template theory: We learn patterns of activity (place along basilar membrane) that are associated with the fundamental frequency and its harmonics. We match the missing fundamental complex to the template (stored pattern) that best matches it.

OR Temporal theory: The comnbined harmonics have a time waveform that repeats at the fundamental frequency, providing the basis of the pitch percept.

 

 

 

  1. Sketch the function that relates detection threshold to the duration of a sound. ALSO: This graph describes what phenomenon? (12 pt)

 

ALSO: temporal integration or summation

 

 

  1. *How would expect a person with abnormally broad auditory filters to perform in a virtual pitch matching test? In frequency discrimination of pure tones? (12 pt)

 

Virtual pitch matching: If the harmonics fell into one auditory filter, could use temporal information and do ok. If harmonics really far apart, might also be ok.

 

Pure tones: good on low frequencies (phase-locking), bad on high frequencies (bad place code)

 

  1. What do I mean when I say that the auditory system has a way of avoiding the sensitivity-resolution trade-off? Briefly describe one theory that attempts to explain how it does that. (12 pt)

 

We can detect very short duration changes (like 5 ms even) in a sound, but still integrate to improve threshold up to 200-300 ms.

Multiple integrators: We have integrators with different integration times and use the ones that work best for a task.

Multiple looks: We only have integrators with short integration times, but use memory to summate information over time.

 

 

  1. What are the two codes that people use to judge the intensity of a sound? Name one condition in which they use both codes. (8 pt)

 

The combined firing rate of auditory nerve fibers with the same characteristic frequency and the spread of neural excitation

 

Pure-tone intensity discrimination at moderate-high levels