When the Brain is attending a cocktail When the Brain is attending a cocktail partyparty

Rossitza Draganova

Cocktail Party ProblemCocktail Party Problem

• The phenomenon how we do recognize what one person is saying or which instrument is playing, or who is singing when other sources around produce sounds at the same time is known as “cocktail party problem”, and introduced by Cherry, 1953

• Collecting knowledge of perceptual processes and internal sensory mechanisms underlying these phenomena are object of auditory scene analysis, Bregmann, 1990.

DEFINITIONSDEFINITIONS

• Streaming – separated streams, fission – stream segregation -, the sound elements (frequency

components) are assigned to different streams - two melodies• One stream – coherent auditory stream, fusion

– stream integration – sound elements are bound into single stream of alternating low and high frequency tones – galloping rhythm

• Isochronous sequence of tones – rhythmic single tone in a sequence

Triplets Paradigm A-B-A Triplets Paradigm A-B-A (Van Norden, 1975)(Van Norden, 1975)

•Presentation rate of A and B tone – SOA of A tones; SOA of B tones•The frequency difference between A and B tone - ∆f

Frequency

Time

A

B

A A

B

A

…

…

“1 streamwith a galloping

rhythm”

…

Triplets Paradigm A-B-A Triplets Paradigm A-B-A (Van Norden, 1975)(Van Norden, 1975)

Frequency

Time

A

B

A A

B

A

…

…

“2 streams,one high and slow, the

other low and fast”

…

0.0

0.2

0.4

0.6

0.8

1.0

0 1 2 3 4 5 6 7 8 9

Time (s)

Pro

babi

lity

'2 s

trea

ms'

res

pons

e

1 ST

3 ST

6 ST

9 ST

The build-up of auditory streaming:a systematic change in the auditory percept over time

during prolonged listening to repeating sequences

TheThe peripheralperipheral channelingchanneling theorytheoryHartmann Hartmann andand Johnson (1991) Johnson (1991)

FrequencyA B

“1 stream”

Level

Frequency

Level

A B

“2 streams”

Horse Morse-LHL-LHL-LHL- --> --H---H---H--

-L-L-L-L-L-L-L

• Segregation takes a few seconds to build up.

• Then between-stream temporal / rhythmic judgments are very difficult

Build-up of segregation

Streaming beyond Peripheral channelingStreaming beyond Peripheral channeling

• Hartmann and Johnson, (1991) - Peripheral Channeling

• Vliegen, J. and Oxenham, A. J. (1999). "Sequential stream segregation in the absence of spectral cues," stream segregation between tones with same auditory excitation pattern, but different periodicities

• Grimault et al., 2002 – Central mechanism, Difference between modulation rates, excluding spectral cues

• Psychoacoustical studies identified different cues which influence the perceptual organization in stream segregation, (Moore & Gockel, 2002; Carlyon, 2004).

Neural basis of streamingNeural basis of streaming

• Neurons still in the AN respond to different frequencies. • Response to frequency of A• Response to frequency of B

• Segregation on the base of frequency separation

– Suppression mechanism (studies in monkeys) – primary auditory cortex

Suppression MechanismSuppression Mechanism

Neuromagnetic Correlates of Streaming in HumanAuditory Cortex.

The Journal of Neuroscience, June 1, 2005 • 25(22):5382–5388 Alexander Gutschalk, Christophe Micheyl, Jennifer R. Melcher, Andre´ Rupp, Michael

Scherg andAndrew J. Oxenham

Neuromagnetic Correlates of Streaming in HumanAuditory Cortex.

The Journal of Neuroscience, June 1, 2005 • 25(22):5382–5388 Alexander Gutschalk, Christophe Micheyl, Jennifer R. Melcher, Andre´ Rupp, Michael

Scherg andAndrew J. Oxenham

A – 250 ms (4 Hz) – pip - 500 HzB - 500 ms (2Hz) – pip – 561Hz / 891Hz

A – 166 ms – 6 HzB – 333 ms – 3 Hz

Triplets Parameters

Pause – 3 s

6sec 6 sec

Independent

A – 200 ms (5 Hz) - 500HzB – 500 ms (2Hz) - 561Hz / 891Hz

A – fc=650Hz; fm=110HzB – fc=650Hz; fm=150 / 235 Hz

Right Ear

B B

A A

Left Ear

Streaming based on central cuesStreaming based on central cues

500 Hz 504 Hz 500 Hz + 504 Hz 500 Hz + 504 Hz

ISI

CB – 4 Hz PB – 4 HzTrial length

test signal length

New methods for investigation of neural bases in New methods for investigation of neural bases in streamingstreaming

• New Paradigms• New stimuli – different stages in auditory system• Additional Neuronal correlates• New data analysis

New New ParadigmsParadigms

1. Peripheral neuronal mechanisms triplets, independent (temporal order)

suppression mechanisms? Transient responses, SSR

2. Central neuronal mechanism

3. Primary stream segregation – build-up

4. Schema-based stream segregation – attention

5. Transition (influence of the context) – triplets

6. Transition – central beat vs. peripheral

New StimuliNew Stimuli

• Peripheral stimuli – pure tones (pips, tone-bursts)• Binaural stimuli – still peripheral (interaural delay)1. binaural – both ears corresponded to different peripheral channels (better

presentation)

2. binaural – both ears have different locations (grouped as separate sources)• Peripheral is better as binaural (Deutsch, 1975)

• Modulated stimuli – central mechanism– dichotic

• Central beat vs. Peripheral beat – dichotic stimuli – central mechanism

Methods for Data analysisMethods for Data analysis

1. Spectral analysis;2. Time-frequency analysis – Wavelet;3. Complex demodulation (Draganova et al., 1999);4. Steady-State responses (SSR)

• representation rate(Periodicity analysis, R.Draganova, 1998);

5. SAM analysis6. Transient responses (P1-N1-P2; SSF)7. Source Analysis

8 sec 16 sec 24 sec 32 sec0 sec

14 sec - TB 14 sec baseline

Scan

Scan

4 sec

BOLD response

Stimuli blocks

Silent fMRI Paradigm Silent fMRI Paradigm

fMRI

Experiment 1• Test Blocks

– Two streams (Pure tones and AM tones, the same ∆f, different presentation rates)

• Baseline– Galloping

– Isochronous stream

Experiment 2• Test blocks

– Central beat

– Peripheral beat

• Baseline• Continuous tone

Thank you for the attention !Thank you for the attention !

Isochronous Stream