Download I. KATZ Chapter 3 PsychoacousticsStudy Guide

Chapter 3 – Psychoacoustics
Psychoacoustics and Audiology
 Psychoacoustics- studying the ____________ process to learn about the ___________
mechanisms (clinical audiology studies an individual’s hearing which is an application of
psychoacoustics)
The Concept of a Sensory Threshold
 Sensations and perceptions of an individual cannot be measured directly, must be
observed from ___________.
 Most common audiometric procedure is measuring a detection _________ (see figure
3.1)
o Here, the strength of a signal is gradually raised from a point where it is not
detectable to a point where it is clearly ___________.
o This is called a _________ __________ and is illustrated in figure 3.1 by the
abrupt change; it has an infinitely __________ slope
 Real life data from __________ testing suggests this isn’t how it works for listeners
 More accurate depiction is shown by the dashed line in 3.1
o Sounds are detected over a range of ______________
o As intensity __________, the probability of the sound being heard increases
o It is not apparent which intensity should be called threshold, rather, it illustrates
that varying intensity changes the probability of __________
 Since detection is a ____________ process, thresholds are subject to __________
o Cause of variability?
 Process of detection is actually quite complex:
 Conversion from ____________ to mechanical energy within the
middle ear
 Transduction of mechanical energy to neural ____________ in the
cochlea
 The propagation of the stimulus through the ________
 The perceptual and __________ processes that ultimately
determine whether the sound is “heard”
 The _________ circuitry associated with responding to indicate
that the sound was heard
 Internal noise of the listener (see figure 3.2)
 We assume internal noise to be Gaussian and always present
How Do We Measure What We Hear
 A discussion of methods used to measure detection thresholds and just noticeable
differences “JNDs”
 Distinction between “classical” and “modern” has to do with the emergence of
___________ detection theory and the procedures that followed from this theory
 3 “classical” psychophysical methods:
o Method of Limits
 Most common method used for measuring ___________ in clinic

Up-down approach much like the ____________________ method
(chapter 5)
o Method of Adjustment
 Quick, simple, straightforward
 Listener has control of the ___________ level and adjusts the value until it
meets a criterion set by the tester
 A tester may instruct the listener to vary the level of a tone until it can
barely be _____________ or until it can no longer be __________
 Dependent on the tester’s ___________ and the listener’s ___________
 Very subjective
o Method of Constant Stimuli (see figure 3.3)
 A set number of stimulus levels are presented _____________, a set
number of times (5 different levels, 5 presentations at each, for a total of
25 presentations)
 At each ________ of presentation, the number correctly detected is
calculated
 Tester picks a percentage to use as _____________ (commonly 50%)
o None of these have addressed ___________ bias (consider differences found
between two people with the same threshold, but one responds conservatively,
and the other more __________; one could be found to have a higher threshold,
though it is really the same)
Signal Detection Theory
 the modern methods view detection as a ____________ process
 See figure 3.5 and discussion
Forced-Choice Procedures
 The usual way this procedure works is for the observer to attend to the __________
observation intervals. In one of the two intervals, a signal will be presented (this is
randomized). The observer must decide which interval contained the signal.
 ___________ can occur in this type of testing (listener may tend to choose the first
interval), however, the influence of a response bias as a result of criterion placement is
virtually eliminated
Adaptive Threshold Techniques
- Threshold is usually defined as the level of a signal that yields a particular proportion
correct on the ______________ function
- Adaptive techniques can _______ the time it takes to find a threshold by choosing levels
that converge towards a certain proportion correct (figure 3.8)
Maximum Likelihood Yes-No Procedure
- uses a “____________” paradigm and therefore had a defined observation period after
which a judgment must be made
- the listener’s response is used to estimate the probability that the response was drawn
from a particular psychometric function chosen from a _______________ set spanning a
range of values
-
as successive levels are tested, the most likely psychometric function emerges and from
that function, _____________ can be determined
advantages:
o it can rapidly and efficiently provide estimates of threshold and ___________ rate
o the _____________ of repeated threshold estimates is high
Perceptual Attributes of the Auditory Stimulus
- Loudness
o all sounds that are ___________ have some degree of loudness
o there is difficulty in measuring loudness, however people generally _______ on
what loudness is and untrained ears can make reliable judgments on degree of
loudness
o most closely related to sound intensity; with all other factors held constant,
changing the ___________ of a sound will change its loudness
 Pitch
o not all audible sounds produce a discernable __________
o can be judged on a scale of _______ to _______, but also on how weak or strong
the perceived pitch is
o a __________ tone has a clear, unambiguous pitch over most of the range of
hearing
o other sounds producing strong pitches include complex ____________ sounds
such as vowel sounds or musical instruments
o for a steady-state harmonic sound, pitch is usually judged as being at or near the
______________ frequency (which is the reciprocal of the period)
o pitch can be mediated by both the place of stimulation in the cochlea and by
timing information from _________ fiber firings
 Timbre
o Sounds can be equal in loudness and have the same pitch, yet be perceived
_____________ (two musical instruments playing the same note)
o this is related to the power spectrum shape and is referred to as ___________
o the study of the ability to discriminate differences in the shape of the power
spectrum is called _____________ analysis
 Loudness, pitch and timbre are the main perceptual attributes of __________
Direct Psychophysical Scaling
- We cannot directly measure the ______________ experience of an observer
- We can however, quantify these experiences based on ______________
- “direct” psychophysical procedures involve the magnitude or quality of a perception
being estimated directly by the observer
- for example: a listener is presented with signals that differ in loudness. After each
presentation, the listener assigns a ____________ based on how loud they perceive the
sound to be. These numbers are then put together to form a __________ of loudness.
Dynamic Range of Hearing
 The _________ range of hearing
 Characterized along coordinates of frequency and __________ pressure level
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Falls between the ___________ curve (threshold) and the loudest ___________ level
(sounds that are too loud to listen to in comfort and/or cause damage)
Studies of the lowest sound pressure level that is just detectable by the human ear as a
function of frequency find two types:
o Minimal audible ____________- measured for individual ears via earphone
o Minimal audible __________- sounds are played over loudspeaker and both ears
are used for detection
the frequency response curves of the ear determined using the two above methods are
similar in that they both have a sharp _______-pass cutoff within the octave between 10
and 20 kHz and both have a shallow ________-pass cutoff around just a few hertz
the main difference in the two curves has to do with _________ versus binaural listening
and that of an __________ ear canal versus an open one
o the unoccluded ear canal has a resonant frequency corresponding to ¼ the
wavelength near ________kHz
o the occluded ear canal’s resonant frequency depends on the distance between the
_________ and the occluding earphone
the frequency response curve of the ear reflects the physical properties of the
____________ membrane (the primary site of tonotopic organization)
physiologic noise such as internal body functions may limit the lowest levels that humans
can hear, especially at very _________ frequencies
the upper limit in level of the usable range of hearing is governed by the perception of
____________ (uncomfortable or damaging tend to define this level)
Sensorineural hearing loss shows a reduction of the dynamic range and can result in
______________ ________________ (the abnormal growth of loudness)
o sounds that would be at a comfortable level for a person with normal hearing
would be uncomfortably loud for a person with ____________
Measuring the “Just Noticeable Difference” or Difference Limen for Pure Tones
- JND- just-noticeable difference
- In experiments measuring JNDs, all variables are held ___________ except for the one
being measured
- The listener is presented with ________ stimuli that differ slightly in regards to one
variable and are asked to tell if the stimuli are the same or different
- Measured for:
o Pitch (DLF; difference limen for frequency)
 For pitch, it is the smallest difference in the frequency of two sounds that
the human ear can detect
 For pure tones, it varies as a function of __________ frequency
 as frequency gets higher, the amount of difference required for the
human ear to detect the two sounds as different becomes
___________
 the DLF also varies as a function of ________ with the DLF
becoming smaller as the signal becomes louder
 as duration goes below about 500 ms, the DLF _________
o Measured for Intensity (DLI, difference limen for intensity)
 Varies less with standard frequency than the DLF
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Decreases slightly for moderate to high level sounds played in
__________
Why are such measures of interest?
o JNDs provide insight into how accurately the ___________ properties of sound
are represented in the auditory system
o JNDs help us to evaluate models of __________ and of the auditory system
o Comparison of JNDs is normal and impaired auditory systems may yield clues to
the loss of accuracy in ________ sounds caused by auditory pathology.
Some Just-Noticeable Difference Measures for Complex Sounds
- there are many aspects of complex sounds that can be varied in discrimination
experiments
- Two fundamental aspects:
o Discrimination of a change in the shape of the power spectrum
 Called ___________ ____________ analysis
 An underlying assumption is that spectral shape discrimination requires
____________ of the intensities at _______ or more frequencies falling in
different regions of the spectrum
 This requires a different approach than that used for ____________ DLI
experiments (see figure 3.9 and explanation on pages 40-41)
 The JND for spectral shape is greatest when the signal falls within the
__________ to ___________Hz range
 The properties of the reference spectrum that allow the greatest sensitivity
to alterations are _________ bandwidth and spacing of components
roughly equal to every 1/3 octave
o Discrimination of a difference in the shape of the amplitude envelope
 Temporal modulation transfer functions (TMTFs) relate the just-detectable
depth of modulation to the ___________ of the modulator
Masking
- Refers to the decrease in the audibility of one sound due to the presence of another
__________
- Used to ensure that the tone is truly being heard in the test ear and is not crossing over
and being heard by the ________-_______ ear
- “masking pattern” curve was determined by varying tones around a masker with
________ intensity and frequency
- “psychophysical tuning curve” was determined by varying the ________ around a
stimulus fixed in frequency and intensity
- the effect of a narrowband masker is greater ___________ the frequency of the masker
than ___________the frequency of the masker
- as the level of the masker increases, this asymmetry or ___________ spread of masking
increases
- when a signal and masker are presented concurrently, certain interactions occur that can
complicate interpretation of results
o beats- audible fluctuations in the amplitude envelope that are a consequence of the
______________ of two or more frequencies
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Temporal Masking- sounds can cause masking even if they do not overlap in time
o forward masking- masking that occurs when the masking sound comes
_________ the signal
o backward masking- masking that occurs when the masking sound comes
_________the signal
Auditory Image Perception and Sound Source Discrimination
- How can humans recognize sounds as separate auditory events that originate from
different sources? How are some sounds recognized as near or far? How can we
discriminate a bird, a voice and the ocean when all the acoustic information is in one
signal?
o Harmonicity- a property that causes discrete tones to be heard as a ________
sound
o Spatial separation- sounds occurring from different _________ typically are from
different sources and this are perceptually ___________
o Onset and offset synchrony and coherent modulation- sounds that begin or end
together are likely to have come from the same _________ and thus tend to be
grouped together perceptually. Common ___________ times with sounds tend to
be very important.
Binaural Hearing
o advantages:
 localization- information on the __________ of the sound source
 suppression of the perception of __________(suppressed fast echoes so
listener can focus on the direct sound source)
 extraction of a desired sound source embedded in many ___________
sounds
o advantage comes from:
 ___________ time difference (caused by the distance between ears)
 ___________ attenuates sound at the far ear creating differences in level
and spectral shape
Psychoacoustic Measures of Listeners with Hearing Loss
o must consider the amount of available _________ range
o testing subjects with hearing loss presents some research problems:
 how do you present sounds? Based on a standard SPL level, or HL
 how do you select candidates for the research as patients with hearing loss
vary so much as a individuals
o the effects of hearing loss depend on multiple factors
 unilateral or bilateral loss
 cause of the hearing loss
 age of onset
 level of loss