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					        CSD 2230

  Normal Sound Perception, Speech
      Perception, and Auditory
Characteristics at the Boundaries of the
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    The Perception of Sound

What do we hear when
 we listen to a
The Perception of Sound

             Psychoacoustics is a
               branch of
               interested in these
               Overview of Perception
n       Although the physical
        characteristics used to
        measure sounds are
        objective, how we
        experience sounds is

Objective Characteristics
    •     Intensity
    •     Frequency
    •     Duration

Subjective Characteristics
          Questions to Ask

 What are the limits of our ability to sense
 How do our subjective impressions of
  sounds change as we change the
  physical dimensions of sound?
Overview of Perception

              How we experience
               sounds is subjective

              Listeners are variable
               in their responses
                Hearing Acuity
What are our limits in
 detecting sounds?

   Audibility and

   Frequency and
    intensity restrictions
Normal Auditory Sensitivity
              Normal hearing listeners
                are capable of detecting
                sounds within a range of
                1 Hz up to about 20,000
              Sensitivity is NOT equal
                across this range
                 Best sensitivity is between
                   1000-5000 Hz
                 As the frequency of the
                   sound moves above or
                   below this range,
                   sensitivity gets
                   progressively worse
                 Auditory Area

n   The useful range of hearing for any individual is
    taken to be the area between the person’s
    absolute threshold and the threshold of feeling
      The Normal Auditory Area
   Useful frequency
    range is between 20
    and 20,000 Hz
   Dynamic range is
    widest between 1000
    and 5000 Hz
   Widest range is 120
Intensities of Common Sounds
   Absolute sensitivity--the minimum
    intensity at which a listener can
    distinguish sound from silence
       ü Detection

   Differential sensitivity--the smallest
    change in a stimulus a listener is just able
    to detect
       n Discrimination
Differential Sensitivity for
                 Intensity discrimination
                  depends on whether
                  sounds are close to
                  absolute threshold or far
                  from threshold
                 In general, for a wide
                  range of stimulus
                  intensities and
                  frequencies, our
                  discrimination ability for
                  intensity is 2 dB or less
Differential Sensitivity for
                 Our resolving power
                  for frequency isn’t as
                  good as for intensity

                 Frequency
                  depends on the
                  general frequency
                  range of the two
  Characteristics of Normal
Sound Perception and Speech
Acoustic Cues of Speech

           1.   Frequency
           2.   Intensity
           3.   Temporal
        Categorical Perception

   Represents an important way in which
    speech is processed differently by
    humans than other sounds

   Illustrated by comparing our ability to
    discriminate and identify certain kinds of
          Categorical Perception

   Discrimination is the ability to tell if two
    sounds are the same or different

   Identification is the ability to label a sound
     Sounds Perceived Non-
n Music
 We can discriminate more than 1000
  different notes (pitches) but most of us
  can only identify about 7.
 Big difference between what we can
  discriminate and what we can identify
Sounds Perceived Categorically
n   Speech

n   We can discriminate the same number of
    speech sounds (phoneme) that we can
    Perception of Some Voiced vs.
        Unvoiced Consonants

   Discriminating /p/ from /b/, /t/ from /d/, or /k/
    from /g/
   These are English consonants that are formed
    the same way (manner of articulation) and
    formed in the same area (place of articulation)
    of the vocal tract but differ in terms of whether
    the vocal folds are vibrating during production
              Voice Onset Time

   The difference in these phoneme pairs is in the
    timing of when the larynx starts to vibrate during
    the production of the consonant
    voice onset time (VOT)
   Voiced stops have a relatively short VOT
   Voiceless stops have a longer VOT
    VOT Waveform for a Voiceless

n   VOT measure for /p/. LO represents the
    release of the burst (stop). RO is placed at the
    highest point of the first cycle of vocal fold
    vibration. Notice the relatively long time interval
    between these two points.
      VOT Waveform for a Voiced

n   VOT measure for /b/. LO represents the
    release of the burst (stop). RO is placed at the
    highest point of the first cycle of vocal fold
    vibration. Notice the relatively short time
    interval between these two points.
    Categorical Perception of VOT

n   Identification functions of a single listener for VOT
    continuum from /d/ to /t/ in 11 ms steps.
The   big question is:
 Are we born with this
    ability to perceive
 speech categorically?
Do we eventually learn
   to perceive speech
Infant Studies
       n   Before birth

          When do we first

          What do we first
                   Infant Studies

    n   Acuity after birth

   How do we measure
   Why is it important to
    know ASAP??
Nonbehavioral Measures of
     Hearing Acuity

               Auditory Brainstem
                Response (ABR)

               Otoacoustic
                Emissions (OAEs)
      Behavioral Responses of
       Infants and Newborns

n   The auditory responses of infants can be
    described in terms of reflexive behaviors
            and attentive behaviors
    Reflexive Behaviors to Loud
n       Reflexes observed
        when loud sounds
        are presented to an

    n     The startle response
    n     The auropalpebral
Attentive Behaviors in
Newborns and Infants
           n   Quieting responses
           n   Increase in ongoing
           n   Changes in breathing
           n   Changes in vocalization
           n   Eye widening and
           n   Smiling or changes in
               facial expression
        Attentive Behaviors in
        Newborns and Infants
n   The intensity of sounds needed to elicit these
    behaviors depends on the type of sound

n   For speech sounds, these behaviors are elicited
    at 60-80 dB SPL
       Behavioral Responses of

n   At around 4 months,
    infants start to
    behaviors consistent
    with localization
Visual Reinforcement

         n   The younger infant 4
             months-9 months
Visual Reinforcement

          n   The older infant 9
              months-2 years
        Infant Speech Perception
   Speech is learned the same
    way as any other motor
   Children DO NOT come into
    the world as blank slates
   Human infants are born with
    the capacity for categorizing
    may speech sounds in
    specialized ways
      Infant Speech Perception
n   Eimas’ studies of the 1970s

    Infant subjects 1-4 months old
    Stimuli included computer generated speech
      sounds that varied in VOT to produce either
      /pa/ or /ba/
    Responses included a non-nutritive sucking
    Results suggested that the infants perceived
      changes in VOT categorically--just like adults
       Infant Speech Perception
n   Werker’s studies of the 1980s:

    English speaking infants from 6 months-12 months of age
    Stimuli included phonemic contrasts from Salish and Hindi
    Responses included a non-nutritive sucking response
    Results suggested that the younger infants listening to the non-
       native contrasts were able to discriminate these speech
       contrasts with good accuracy, but the ability disintegrates
       progressively as the child ages
    Their ability to discriminate contrasts in their native language
       remained high
    Three Important Conclusions
    Regarding Speech Perception
   Infants already come into the world with certain
    perceptual capacities for phonetic distinctions
    used in the world’s languages
   Experience with a particular language leads to
    decreased perceptibility of at least some non-
    native phonetic contrasts and enhanced
    perception of native contrasts
   By the end of the first year, the influence of a
    particular language is evident in the perception
    of non-native speech
                  Older Adults

   Changes in acuity
    usually begin around the
    third decade of life
   Incidence increases
    sharply as we age
   25%-40% of people over
    65 have significant
    hearing loss
   The figure changes to
    90% by the time we
    reach our 80s
Hearing Loss and Aging

                No clear etiology (cause)
                Possible sources include:
                  •   Noise exposure
                  •   Genetics
                  •   Vascular disease
                  •   Systemic disease
                  •   Diet
                  •   Pollution
                  •   Others
     Audiologic Characteristics
      Associated with Aging

n   Acuity:
n   Changes in pure tone
    sensitivity (absolute
    thresholds) among
    older adults emerges
    gradually as age
      Changes in Detection as a
     Function of Age and Gender
n    Two trends are clear from these data:
1)   Both males and females exhibit a
     significant loss in sensitivity by age 60,
     especially in the higher frequencies
2)   Threshold values for males are poorer,
     overall, than for females
Audiologic Characteristics
 Associated with Aging
                  Abnormal growth of loudness
                   commonly associated with
                   damage to the cochlea
                  Due directly to the reduced
                   dynamic range
                  Makes the ear more sensitive
                   to loud sounds
      Audiologic Characteristics
       Associated with Aging
n   Speech Perception

n   Speech perception
    suffers as we age, even
    if we control for the
    change in sensitivity
    associated with aging