Acoustic Illusions

1
Acoustic Illusions Sound Segregation

• Reading Assignments
• for Quizette 3
• Chapters 10 11

2
TLA 5 Hearing in Space

• HIS DUE Nov. 8
• Ingredients
• Large area
• Pen paper
• Activity
• Close your eyes and listen for 1 minute
• Try to identify the sound sources
• Write-up
• How many sounds did you hear?
• What made those sounds distinctive?

3
Timbre Illusion Shepards Scale

• The musical equivalent of M. C. Escher
• When does this scale reach the highest note?
• PLAY DEMO
• What is Sheppards scale?
• Notes are actually chords
• Highest/lowest notes in chord are replaced for
  successive frequency changes
• Illusion of timbre
• Misattribution of fundamental frequency

4
Timbre Illusion Interval Size

• Two intervals, which interval is larger?
• PLAY DEMO
• Note brightness of timbre for each interval
• PLAY DEMO again
• Bright-to-dark sounds larger
• Works for musicians untrained listeners
• Timbre affects pitch perception

5
Deutsch Melody

• Melody played across two ears
• Within each ear large intervals (1 octave)
• Ascending/Descending melody can only be heard if
  ears are combined
• Listener hears 2 coherent scales
• Melody is constructed by suppressing irrelevant
  tones
• Suggests What or Where theory of brain

6
What or Where?

• Is auditory perception duplicitous?
• What Objects sequences
• Process of organization
• Melody
• Object recognition
• Where location, location, location
• Interaural processing
• Spectral cues for spatial position
• Motion
• Neural evidence (e.g., Berlin Zatorre, 2000
  Read et al., 2002 Romanski et al., 2000)
• Dorsal pathway - spatial
• Ventral pathway - identification

7
What causes sounds to group into streams?

• Gestalt grouping (see Bregman, 1990 for review)
• Perceptual laws to combine cues
• Bottom-up processes/Automatic
• Hierarchical organization
• Highly applicable to auditory perception
• DEMO Galloping Sounds
• Large Step then Small Step
• Bach Chorale 1 2
• Traffic
• Laws of proximity (close in time), similarity
  (same timbre/pitch)
• Law of Pragnänz simplest solution

8
Neural Correlates of Stream Segregation

• Summation of cortical response hypothesis
• (DRAW) Will a stimulated area summate with
  another stimulated area on the tonotopic map?
• Tetanic rapid stimulation increases probability
  of summation (Fishman et al., 2001)
• ALTERNATIVELY?
• Lesions of temporal cortex (in and around primary
  auditory cortex) (Peretz and colleagues, 1999
  2001)
• Poster temporal gyrus affects melodic grouping
• Intervals, melodic contours
• Anterior temporal gyrus affects meter
• Rhythmic grouping, temporal combinations