Binaural Interaction D. Deutsch's Auditory Illusions

1
Binaural InteractionD. Deutsch's Auditory
Illusions

• Wes Hatch
• PSYC 501
• Prof. Bregman
• Nov. 21, 2002

2
Introduction

• Review of streaming attributes
• Octave illusion and Chromatic illusion, initial
  conclusions
• Scale illusion and initial conclusions,
  listening examples
• Critiques and questions
• Other data and ideas for future research
• Questions

3
Review of Streaming Attributes

• Perception and streaming influenced by several
  competing modules (Bregman)
• Gestalt grouping principles (proximity, common
  fate, good continuation, etc.)
• Do certain attributes contribute more than
  others? (ie. get priority, 'win' over other cues)

4
Review of Streaming Attributes

• Some cues for organizing auditory info (concerns
  stimulus attributes)
• Frequency (or frequencies of its components)
• Good continuation
• Spatial location (lateralization)
• Amplitude

5
Introduction to the Illusions

• all stimuli presented at 250 ms/tone, no breaks
  in between
• different stimuli/attributes to each ear
  (dichotic listening)
• Binaural presentation allows certain attributes
  to be placed in opposition
• ie. grouping by location vs. grouping by frequency

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Introduction to the Illusions

• which are the dominant cues used for musical
  tones?
• variations between listeners in how these are
  perceived
• Disagreements tend to arise between righthanders
  and lefthanders

7
Octave Illusion
8
Octave Illusion

• channeling by spacial location, even though
  simultaneous input
• sort high and low sounds into two separate
  streams
• no one reported hearing two sounds at once!
• frequencies at only one ear (the dominant ear)
  are followed/tracked
• Localization perceived to be wherever the high
  tone is
• What people heard and where they heard it coming
  from was based on pitch information alone

9
Octave Illusion

• Two different selection mechanisms underlying
  pitch and localization perceptions
• handedness influences which is the dominant
  ear (right-handers hear high tone on the right,
  left-handers vary)
• when headphones were reversed, most listeners
  discerned NO change in perception

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Octave Illusion

• strange, alternate perceptions
• single tone which switches from ear to ear, whose
  pitch changes only slightly
• low (or high) tone which switches from ear to ear
  whose pitch shifts by a semitone, together with
  an intermittent high (or low) tone in one ear.
• timbre differences
• different illusions at different times pattern
  appears to be constantly changing

11
Octave Illusion

• We unconsciously assume similar pitches eminate
  from one source and different pitches from
  different sources.
• amplitude plays a small part. A critical level
  of about 6dB at the non-dominant ear before
  intensity a factor
• where is this interpretation/interaction taking
  place?
• neural pathways with information from different
  regions of audio space?
• pathways specific to information from each ear?
• Higher or lower order brain function? In the ear
  itself? Etc.

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Glissando illusion (Deutsch, 1995)

• we perceive glissando to be continuous
• oboe tone is heard as jumping back and forth
  segments of the glissando appear to be joined
  together seamlessly
• Right-handers most often hear it as travelling
  from left to right as its pitch glides from low
  to high, and vice versa

13
Scale Illusion
14
Scale Illusion

• tests proximity (of pitches), good continuation,
  laterality
• if proximity wins, should hear arc patterns.
• if good continuation wins, should hear linear
  trajectories (ie. scale)
• if laterality, should hear original stimulus

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Scale Illusion

• Channeling on basis of frequency range wins!
  (proximity)
• 2 lines heard lower higher
• Higher tones eminating from right ear (for most
  right-handers), lower tones from the other
• grouping by good continuation never occurred
• Organization by spatial location never occurred
• location and pitch are analyzed by different
  mechanisms, with output of these mechanisms
  integrated at a later stage

16
Scale Illusion

• when headphones were reversed, most listeners
  discerned NO change in perception.
• seems reasonable that listener assumes tones in
  one frequency range are from one source, and
  those in another range are a different source
• These findings may be extended and applied to a
  wide range of music

17
Scale Illusion

• works for similar stimuli (chromatic illusion,
  Deutsch '87)
• also works over speakers (Butler, 1979)
• timbral differences introduced listeners
  perceived a new tone quality originating from
  both speakers
• amplitude differences have little effect on
  streaming
• gross mislocalization effects
• Input to both ears simultaneously gives poor
  localization cues
• other, alternate perceptions

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Scale Illusion Segue

• two types of auditory processes going on?
• independent modules speech and music
• if input is a melodic pattern why cant
  listeners follow each stream, and report
  note-patterns at each ear? Why can we do this
  for speech and not for simple tones?
• percept is likely a result of training/conditionin
  g (Davidson, 1987)
• how will percept change with more complex
  stimuli?
• Spectral cues
• Listeners able to follow speech because they've
  had life experience to this end

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Critiques and Questions

• not real-world stimuli
• why do musicians or anyone with significant
  musical training respond differently on these
  tests? Composers even reacted differently than
  performers (Davidson, 1987)
• Suggests experience and learning both play a
  part (esp. for scale illusion)
• Deutsch's subjects musical training or not?
  Results hard to evaluate

20
...Regarding the Octave Illusion

• Stimulus is a special condition. 21 frequency
  relationship
• tone on one side is same as what was just on
  other
• Induces melodic chanelling by spacial location
• do tones somehow interact to produce a 2-tone
  complex?
• are we localizing just one complex tone?
• Asynchrony of tones (Bregman Pinker) an
  infl'nce?
• results may be due to listeners memory

21
...Regarding the Scale Illusion

• results may be influenced by
• musical training of subject, and expectation of a
  musical line (Smith et al., 1982)
• narrowing/confining listener's responses to only
  a few choices (Smith et al., 1982)
• priming (Davidson et al. 1987, Dowling 1973)
• Learning
• stimulus crossing points, first and last notes,
  total number of notes
• biased responses (Radvansky et al., 1992)
• Crossing trajectories negate any good
  continuation

22
...Regarding the Scale Illusion

• crossing points one middle note (as opposed to
  two) is LESS conductive to proximity organization
  (Radvansky et al., 1992)
• first last notes may be used as anchor
  points (Radvansky, 1992)
• Radical shift in listener response when stimuli
  altered (Radvansky, 1992)
• we may conclude that the exact nature of the
  stimulus is influential in the perception

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Other Scale Illusion Data

• 90 of musicians localized higher tune in right
  ear (Smith et al, 1982)
• altered stimuli (Radvansky, 1992) experiment
  with a closed set of responses to choose from
• response D D1
• Arcs (proximity) 40.9 17.4
• Linear (good cont) 11.2 22.9
• Jagged (even notes) 19.8 (correct) 22.7
• Jagged (odd ) 12.5 23.6 (correct)
• Other 2.3 1.3
• Dont know 6.8 6.4

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Conclusions

• Binaural interaction plays a part in all
  illusions
• Symmetry of stimuli
• When two signals are separated in time, spatial
  organization is strong
• All attributes contribute to streaming, but some
  more so than others, given the context (certain
  cues dominate for certain tests)
• except amplitude differences. These seemed to
  produce weakest cues for streaming

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Future Research Ideas

• Examine the many perceptual variances in these
  illusions
• How to interpret/explain differences
• Symmetry of stimuli influential to what extent?
• Research to explain why listeners can track two
  speech streams, rapidly alternating, but with
  tones get confused
• why is glissando in glissando illusion heard as
  continuous?
• Timbre, or because of gliss? Does the addition
  of another stream influence perception?

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Future Research Ideas

• need more research contrasting differences
  between musicians and non-musicians
• examine differences in brain organization
• Examine responses based on handedness
• how does handedness correlate?
• why are most right handers more uniform in their
  perception, whereas lefties vary widely
• suggests neural differences may be accountable
  for how we process these stimuli
• correllated with brain lateralization. Lefties
  may be the same or opposite as right-handers