PSYC 182
Auditory Illusions
Illusions: General Features
• False perception or belief
• Perceptual system
dislikes ambiguity
– Resolves ambiguity
– sometimes illusions
• Perceptual organization
– Gestalt Principles
– generally correct
– but not always
Illusions: General Features
• Illusions -> insight into brain limitations
• Perceptual system interprets new info
– Uses past experience, memory, beliefs…
Illusions vs Hallucinations
• Illusion: distortion of the senses
– Misinterpretation of actual sensory stimulation
• e.g. hearing words in radio static
• Hallucination: perception without stimulus
– e.g. hearing words in the absence of sound
– Overactive top-down processing -> output
– differentiating internal & external info breaks down
– Activity in secondary sensory processing areas
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Grouping Mechanisms
• Gestalt Concepts
– Proximity
Picket fence effect
• Gliding tone
‘continues’ through
noise bursts
– Similarity
– Continuity
– Common fate
– Familiarity
Continuity
• Continuity in noise
burst
Applied streaming segregation
• Two interleaved
melodies blend into
one.
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Grouping demo: proximity
• Slow: 1 melody
• Fast: 2 melodies
• Grouped by
proximity
Scale illusion
• Spatial reorganization
• Proximity & Continuity
• Handedness
Scale illusion
• Musical Implications:
• Orchestral seating
– High stage-right, low-left
• Rules of voice leading
– Too many leaps
– Avoid crossover
• Tchaikovsky’s 6th Symphony
– Melody split up
– between 1st, 2nd violins
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Chromatic illusion
Cambiata Illusion
Glissando Illusion
Octave Illusion
• Oboe tone alternating with sine wave
glissando
• Different percepts
– Typically, oboe alternates
– Glissando: low-left to high-right
• High pitch->location
• Dominant ear-> pitch
• Implications:
–
–
–
–
Handedness
What vs. Where
Binding problem
Echo suppression?
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Phantom Words
• Ambiguous
• Percepts include:
SPECTRAL
(FOURIER)
ANALYSIS
– what’s on one’s mind
– other languages
– Knowledge about the word
Harmonic Fusing and Common Fate
Brain combines frequency components into one pitch
-Gestalt law of common fate
-Harmonics begin, shift, and end at the same time
- Calculated based on common denominator of partials
Harmonic Fusing and Common Fate
Missing fundamental a.k.a. Virtual Pitch
-Fundamental frequency (f0) = perceived pitch
-even if fundamental is missing!
e.g. 100 Hz, 200 Hz, 300 Hz, 400 Hz, 500 Hz = 100 Hz
200 Hz, 300 Hz, 400 Hz, 500 Hz = 100 Hz!
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Pitch – Perceptual Phenomena
Proximity: Shepard tones
• Octave-related
complexes
• Follow by proximity
– pitch class circle
– smaller intervals
Octave equivalence – a note doubled in frequency
sounds similar to the original
• cross-cultural (cross-species?)
• perceptual quality is “chroma”
• pitch = “chroma” + “height”
“SHEPARD’S ILLUSION”
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