Task 8: Auditory localisation and organization Flashcards
In addition to distance, sounds can be located in other two dimensions
- Azimuth = from left to right
- Elevation = from up to down
Cues for localisation
Binaural and Monaural
Binaural cues for localisation
- informations reaches both ears to determine azimuth of sound
- interaural time difference
- interaural level difference
Interaural time difference ITD
- difference between when sound reaches left and right ear
- info about low-frequency sounds (large spacing)
- determines speed of neural processing
- ITD becomes larger as sources are more located to the side
Interaural level difference ILD
- difference in pressure level of sound
- acoustic shadow = reduces intensity of sounds reaching the far ear (occurs only for high-frequency sound)
Cone of confusion
- no information about elevation
- two points have the same ITD and ILD
Monaural cues for localisation
- elevation coordination => spectral cue
Spectral cue
- differences in distribution of frequencies reaching each ear from different locations
- works especially at higher frequencies
- head, pinae and ear canal are important
- head related transfer function
Head related transfer function
spectral (frequency) feature of sound is changed depending on the sound elevation
Auditory pathway and cortex
- hair cells in the cochlea
- nerve fibers
- cochlear nucleus
- superior olivary nucleus in the brainstem (signals from both ears meet here)
- inferior colliculus in the midbrain (binaural processing happens here)
- Medial geniculate nucleus (thalamus)
- Primary Auditory Cortex A1
Primary Auditory Cortex include
Core Area = A1
Belt = surrounds core => precise information about location
Parabelt = ventral to the belt
Two auditory pathways for audition extend from
temporal lobe to frontal lobe
What Pathway
- from anterior part of core and belt to the prefrontal cortex
- identifies different types of sounds: complex sounds, timbre, missing fundamentals
- auditory illusions
- auditory grouping and segregation
Where pathway
- from posterior part of core and belt to the prefrontal cortex
- locating sounds
- better spatial tuning
Auditory scene analysis
multiple sound sources in auditory scene are separated or grouped into sound images
Principles that help organise elements of auditory scene
- Location = cues such as ITD and ILD + continuous path of movement
- Onset time = different time of onset => different sources
- Pitch and timbre
- same timbre => grouping by pitch
- different timbre => grouping by timbre
- same timbre and pitch range are often produced by the same source - Auditory continuity = same frequency
- Experience = comparing what we hear to a (melody) schema
- Harmonicity and timing
The Scale Illusion
- successive tones in each scale alternate between left and right ears
- right handers: high tones = right earphone
low tones = left earphone - left handers: mirror image of right handers or even more complex
