AHOP - TASK 4
AUDITORY SCENE ANALYSIS
Auditory scene
analysis
No information
which vibration is created by
which source (e.g. instrument)
Auditory scene
array of sound sources
in environment
Auditory scene analysis
Multiple sounds at same time (e.g. symphonic orchestra)
separation of multiple stimuli
produces by each of the sources
in the scene into separate perceptions
deciding which frequency components
belong together to form each sound
Principles of auditory
grouping (gestalt, cues)
PLACE
same source = same place,
movement (mostly)
TIMBRE, PITCH
same source = same pitch/timbre
ONSET TIME
same source = start same time
PROXIMITY IN TIME
repetition rate rapid = same source
Auditory stream
grouping (integration)
same source, same onset, same pitch/timbre, close in time (synchrony)
one stream, object
Auditory stream
segregation
two streams, two objects
diff source, diff onset, diff pitch/timbre, far in time (asynchrony)
separation of two
experiments
Tonotopic map
Large diff frequency = non-overlapping
Neural adaption
Forward suppression
ELHILALI
FISHMAN
Behavioural
experiment
Neural correlate
synchrony/coherence is primary
(overrules high freq separations)
physiology
Psychophysics
Computational modeling
thresholds for detection
humans
informal listening
single stream = lower threshold
two streams = higher threshold
last tone slightly shifted temporally
segregation (asynchrony) = hard to detect
Experiment 1
single unit recording (A1)
ferrets
fixed freq separation
(1, 0.5, 0.25 octaves)
Segregation
1, 0.5 octaves
Grouped
(0.25 octaves)
Synchronous = always grouped
(irrespective of delta freq)
synchronous, overlapping
and alternating presentation
No neuronal correlate found
(firing rate same for all presentation modes)
strongest response
BF site
Experiment 2
frequency range
of interactions
A (BF) tone fixed,
B changed
No neuronal correlate found
(firing rate pattern same)
Temporal coherence is
fundamental orgnaising principle
temporal integration
coherence analysis
spatio-temporal hypothesis
PFC? Attention?
Failed to find neuronal correlate
Auditory scene analysis
Auditory systems groups and segregates components of mixtures to construct perceptual representations of sound sources (auditory images)
Gestalt principles
Auditory stream segregation
sequential organisation
one stream
slow PR
small freq separation
Two streams
fast PR
high freq separation
MUA & CSD
complementary techniques
Neural populations
Monkeys
Stimuli
Alternating frequency (AF)
Same frequency (SF)
Best frequency (BF), tone A
non-BF, tone B
A1
Results
Same frequency
Alternating frequency
Reversed order
(no difference, A dominant)
A higher response (BF)
higher PR = decrease response
higher PR = decrease response
B (non-BF) faster decrease
40Hz = only response to A
at half of PR (20 Hz)
Model of neural
stream segregation (A1)
CSD-methods
Source = negative
Sink is positive
Same results as MUA
Attention biases
stream segregation
Intermediate freq
separation
dependent of PR
small freq
separation
overlap
grouped, response both
decrease response fast PR
high freq
separation
no overlap
segregation
decrease amplitude higher PR
preferential processing at 40 Hz
Proposed mechanism
Forward masking
/suppression
suppression of subsequent responses
Source (inhibitory) after
sink (excitatory)
BF tones more effective
in subsequent suppression of non-BF
BF response larger under SF
than AF (less suppression)
BF suppresses next BF more
increase suppression
non-BF with increase separation freq