Identification and discrimination of the relative onset time of two component tones: Implications fo

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Identification and discrimination of the relative
onset time of two component tones Implications
for voicing perception in stops

• David B. Pisoni (1976-77)

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Past Studies

• Lisker and Abramson (1964, 1970)
• Liberman et al.
• Mattingly, Liberman, Sydral, and Halwes
• Eimas (1971)
• Kuhl Miller (1975)
• Lasky
• Streeter
• Miller et al

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Lisker and Abramson

• They investigated
• Voicing and aspiration differences shown across
  different languages (last class)
• Differences in timing and glottal activity
• They discovered 3 modes of voicing (1964)
• Pre-voiced stops voicing onset precedes the
  release burst (negative onset, -VOT)
• Short-lag voiced stops voicing onset is
  simultaneous or briefly lags behind the release
  burst (0 VOT)
• Long-lag voiceless stops in which the voicing
  onset lags behind the release burst (positive
  onset, VOT)

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Liberman

• In perceptual experiments done with synthetic
  stimuli they found (1961)
• Subjects ID and discriminate differences in VOT
  in a categorical-like manner that reflects the
  phonological categories of their language
• Consistent labeling with sharp crossover points
• Discontinuities in discrimination that are
  correlated with the abrupt changes in the
  labeling functions
• Better at discriminating 2 synthetic stimuli from
  2 different phonological categories vs. from the
  the same

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According to Several

• Empirical Findings
• Non-speech signals are perceived in a continuous
  mode
• No other categorical perception studies had been
  done with synthetic stimuli
• Non-monotonic discrimination functions are the
  result of labeling processes associated with
  phonetic categorization
• Interpretation
• Evidence for the operation of a special mode of
  perceptionSpeech Mode

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Liberman et al. (1961) Mattingly, Liberman,
Syrdal and Halwes (1971)

• Are discontinuities in speech discrimination
  functions due to the acoustic or psychophysical
  attributers of the signals themselves rather than
  some speech related labeling process?
• Found no peaks in the non-speech discrimination
  functions at phoneme boundaries so
• Conclusion Speech Mode
• discrimination of speech stimuli were
  attributable to phonetic categorization resulting
  from the stimuli being perceived as speech.

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Eimas (1971)

• 2 and 3 month old infants
• Found that they can discriminate synthetic speech
  sounds varying in VOT much like English speaking
  adults
• Implication infants have access to mechanisms
  of phonetic categorization
• Innate mechanisms
• Responding to phonetic coding VS. psychophysical
  differences
• Environment plays a secondary role

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Kuhl and Miller (1975)

• Study done with chinchillas
• Trained to respond differently to the consonants
  /d/ and /t/ (human voice)
• Used synthetic stimuli varying in VOT with a
  sharp crossover point
• The discrimination functions were similar to
  English speaking human databut chinchillas dont
  have spoken language
• Suggests a psychophysical basis VS. phonetic
  basis for the labeling behavior
• Results the boundary for voiced and voiceless
  labial stops occurs at about 25 msecthreshold

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Lasky et al. (1975)

• Cross-language studies
• 4 to 6 1/2 month old infants born to
  Spanish-speaking parents
• Found evidence for 3-categories in discrimination
• Boundary occurred in the region of 20 msec and
  60 msec (corresponds to the English
  voiced/voiceless times)
• And at -20 msec and -60 msec
• Spanish only has one phoneme boundary b/w voiced
  and voiceless stops and it does not coincide with
  the boundaries they found
• Conclusion
• Environment plays minor role
• Responding to psychophysical attributes

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Streeter (1976)

• Kikuyu infants (Kenya)
• Show evidence of 3 categories of voicing for
  labial stops
• Kikuyu have no voicing contrasts for labial stops
  (but they exist at other articulation places)
• Conclusion
• They had not been exposed to these before
• Responding to psychophysical attributes
• Similar to the Laskey et al. research

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Miller et al. (1976)

• Non-speech control signals
• Using VOT in the form of a noise bust and a buzz
• Adults
• Results discrimination functions that were
  similar to those found with stop consonants
  differing in VOT
• Discrimination was excellent for stimuli selected
  from b/w categories and poor for stimuli within a
  category
• Perceptual threshold
• Psychophysical account

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Pisoni

• Independent from Miller et al. but at the same
  time
• Used stimuli that varied in temporal order of the
  onsets of 2 component tones at 2 frequencies
  (Figure 1)
• 500 Hz
• 1500 Hz
• -50, 0, 50 msec VOT (ranging in 10 msec
  increments)

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Pisoni

• Goals
• To learn something about how the timing relations
  in stop consonants are perceived
• To provide a more general account of the diverse
  findings obtained with adults, infants and
  chinchillas on VOT stimulus
• To provide an account of the results obtained
  with non-speech stimuli

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Pisoni Experiment I

• 8 paid volunteers from ad in student paper
• All were right handed and native English speakers
• Stimuli (Figure 1)
• 11 digital two-tone sequences
• Lower tone 500 Hz
• Higher tone 1500 Hz
• Variable is VOT
• -50
• 0
• 50

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Pisoni Experiment I

• Stimuli was presented at 80 dB SPL
• 2 one-hour sessions done over 2 days
• Day one
• Identification training sequences
• Presented with the endpoint stimuli (-50 50)
• Told to learn (w/their own strategy) which one of
  the 2 buttons was associated w/ea sound
• Immediate feedback for correct responses

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Pisoni Experiment I

• Day two
• Tested for identification
• 11 stimuli presented in random order
• No feedback
• Tested for ABX discrimination
• 9 two-step pairs along the continuum
• Feedback provided for correct responses
• Told to determine whether the 3rd sound (X) was
  most like the first (A) or second (B) sound
• Chance performance

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Pisoni Experiment I

• Figure 2 (p.1355)
• Filled in circles labeling functions response
  to 2 end points
• Sharp and consistent for some
• Crossover points for the category boundary for 6
  of the 8 are not at 0 but are displaced towards
  the lagging (50) stimuli
• Why?

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Pisoni Experiment I

• Possibly due to limitation on the processing of
  temporal information or
• Due to Masking of the high frequency (1500 Hz) by
  the low (500 Hz)
• So, they accounted for that by running a pilot
  study
• Pilot study (p.1355-56)
• Results they found no shift in boundary location
  sothe Limitation on the Processing of Temporal
  Information is the more like cause of asymmetry

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Pisoni Experiment I

• ABX-discrimination results
• Open circles Fig. 2
• Categorical-like discrimination
• Peaks and troughs
• S2 ideal

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Pisoni Experiment I

• Results from ID and ABX
• Categorical perception with non-speech signals
• This form of perception is not unique to speech
  signals
• Removes one positive line of evidence for the
  Speech Mode theory
• Questions
• Are the findings due to labeling process brought
  about by the training process?
• Or is it do to a simpler psychophysical
  explanation?

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Pisoni Experiment II

• Goal (in order to answer the previously asked
  questions)
• To obtain ABX-discrimination functions before any
  training experience (label training)
• If peaks in discrimination exist there will be
  reason to suspect a psychophysical basis for the
  observed discrimination functions from E1

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Pisoni Experiment II

• 12 volunteers
• Same 11 stimuli used in E1
• 2 one-hour sessions held on separate days (no
  label training)
• 360 ABX trials done ea. day with feedback
• 9 two-step stimuli comparisons were responded to
  80x by ea subject

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Pisoni Experiment II

• Results
• Figure 3 (p. 1357)
• 2 patterns shown (except S1 chance)
• Single peak _at_ approximately 20 msec
• Double peak _at_ approximately 20 and -20
• Natural categories are present at places along
  the stimulus continuum marked by narrow regions
  of high sensitivity (thresholds)
• 3 categories corresponding with the temporal
  events
• Lower tone leading by 20 msec or more (-)
• More or less simultaneously within the -20 to 20
  msec region
• Lower tone lags by 20 msec or more ()

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Pisoni Experiment II

• These results contrast
• Liberman et al. (1961)
• Mattingly et al. (1971)
• The above both found
• Marked differences in discrimination between
  speech and non-speech signals
• Why?

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Pisoni Experiment II

• The lack of familiarity with the stimuli used
  (Liberman synthetic spectograms of /do/ and
  /to/ Mattingly 2nd formant transitions were
  isolated from the rest of the stimulus pattern)
• The absence of any feedback during the
  discrimination task
• With complex multidimensional signals it may be
  difficult for subjects to attend to the relevant
  attributes that distinguish these stimuli

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Pisoni Experiment II

• Patterns of categorical perception are seen when
  using speech and non-speech stimuli

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Pisoni Experiment III

• Goal
• To demonstrate that subjects can classify these
  same stimuli into three distinct categories whose
  boundaries occur at precisely these regions on
  the continuum

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Pisoni Experiment III

• Same training procedure
• Except3 responses instead of 2
• 8 additional subjects were recruited
• Same set of 11 tonal stimuli
• Took place on 2 separate days

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Pisoni Experiment III

• Day 1
• Shaping and identification training with the 3
  stimuli (-50, 0, 50 msec)
• Subjects were free to adopt their own coding
  strategies
• Immediate feedback was provided
• Day 2
• Labeling tests were conducted

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Pisoni Experiment III

• Figure 4 (p. 1358)
• All subjects partitioned the stimulus continuum
  into three well-defined categories
• Boundaries found at approximately -20 and 20
  msec
• Perceptual threshold
• Ability to discriminate temporal differences

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Pisoni Experiment IV

• Goal
• Simultaneous vs. non-simultaneous.
• Having the subjects determine whether there are
  one or two distinct events at stimulus onset

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Pisoni Experiment IV

• 8 additional volunteers
• None had participated previously
• Same 11 tonal stimuli
• A single 1-hour session
• 11 stimuli presented randomly
• Told to listen to ea sound carefully and then
  determine whether they could hear one or two
  events at stimulus onset
• No feedback was given

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Pisoni Experiment IV

• Figure 5 (p. 1359)
• All subjects showed similar U-shaped functions
  with sharp crossover points between categories
• Results
• The presence of 3 natural categories that may be
  distinguished by the relative discriminability of
  the temporal order of the component events

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Pisoni Findings

• A perceptual effect for processing temporal order
  information which may also underlie the
  perception of voicing distinctions in stop
  consonants in initial position
• There is a perceptual threshold (consistent with
  studies done by Hirsh, Hirsh and Sherrick, and
  Stevens and Klatt) of about 20 msec

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Pisoni Findings

• We knowthat VOT (in terms of onset of voicing)
  must be judged in relation to the temporal
  attributes of other events (release from closure)
• So, these events are ordered in TIME, therefore
  highly distinctive and discriminable changes will
  be produced at various regions along the temporal
  continuum
• Phonological systems apparently have exploited
  the principle of discriminating discrete
  attributes (natural categories) during the
  evolution of language
• In other words, weve positioned our phonemes on
  either side of the natural auditory boundary
  provided by the threshold