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Auditory perception classes: critical bands/auditory filters David Poeppel Questions/complaints/ concerns: [email protected]

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Auditory perception classes: critical bands/auditory filters. David Poeppel Questions/complaints/concerns: [email protected]. - PowerPoint PPT Presentation

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Page 1: Auditory perception classes: critical bands/auditory filters

Auditory perception classes:critical bands/auditory filters

David PoeppelQuestions/complaints/concerns:

[email protected]

Page 2: Auditory perception classes: critical bands/auditory filters
Page 3: Auditory perception classes: critical bands/auditory filters

QuickTime™ and a decompressor

are needed to see this picture.

Coronal slice illustrating auditory pathway from ear to auditory cortex

Coronal slice (structural MRI) illustrating localized activation in superior auditory cortex (upper bank of superior temporal gyrus) to sinusoidal tones of different frequencies.

Page 4: Auditory perception classes: critical bands/auditory filters

Auditory system

Kandel 2000

Page 5: Auditory perception classes: critical bands/auditory filters

AVCN PVCN DCN

LSO MSO MNTB

DNLL VNLL

ICc ICp ICdc ICx

A1 R RT

MGv MGd MGm Sg/Lim PM

CL CM ML

CPB

RTMRTLALRM

10, orb12vl46d8a

TS1, 2

RPB

Tpt STS

Contralateral cochlear n.

Sup. olivary complex

Lateral lemniscus

Midbrain

Thalamus

Core

Belt

Parabelt

Temporal lobe

Frontal lobe

Kaas & Hackett , PNAS 97, 11793 - 9 (2000)

Page 6: Auditory perception classes: critical bands/auditory filters

Hall & Garcia, 2012

Page 7: Auditory perception classes: critical bands/auditory filters

Auditory cortex

Medial geniculate body

Medial geniculate body

Inferior colliculus Inferior colliculus

Auditory cortex

Superior Olivary Complex

Superior Olivary Complex

Cochlear Nucleus Cochlear Nucleus

Left Cochlea Right Cochlea

Lateral lemniscus

Lateral lemniscus

Chandrasekaran & Kraus 2009

Page 8: Auditory perception classes: critical bands/auditory filters

Hickok & Poeppel, 2007, Nat Rev Neurosci

Functional anatomy of speech sound processing

Page 9: Auditory perception classes: critical bands/auditory filters

A few reminders about the characteristics

• Frequency range of human auditory system– 20 Hz to 20,000 Hz (textbook); 50 Hz to 10,000 Hz (really); most

psychophysics is done between 100 - 5,000 Hz (because that is the range in which one obtains interpretable data).

• Intensity range– Extends over many orders of magnitude (depending on frequency); at

the ‘sweet spot’ (~1000-3000 Hz) about a 120 dB dynamic range

• Sensitivity– JNDs for frequency: ~0.2% (e.g., at 1000 Hz base frequency, listeners

can distinguish 1000 Hz from 1002 Hz -- impressive!)– JNDs for loudness discrimination: ~1 dB– Sensitivity to timing differences: a few microseconds in spatial hearing

(JNDs for azimuthal localization ~1 deg); 2 milliseconds (gap thresholds); 25 milliseconds (order threshold). Really impressive …

Page 10: Auditory perception classes: critical bands/auditory filters

Absolute threshold of hearing in quiet

audiograms

Page 11: Auditory perception classes: critical bands/auditory filters

Perceptual attributes of sounds

• Spatial location– Binaural hearing (inter-aural time and intensity differences), head-

related transfer function.

• Loudness– Signal amplitude (ASA Demos 8-11, compare 6/3/1 dB steps)

• Pitch – sound frequency, fundamental frequency of complex periodic signals,

or inter-harmonic spacing

• Timbre– Distribution of energy across frequency, shape of the spectrum

The frequency resolution/processing of the system underlies the construction of perceptual attributes.

Page 12: Auditory perception classes: critical bands/auditory filters

Pure vs. complex tones (all A440) - pitch, timbre, phase

T (= 2.27 ms) t

pitch is (largely) phase invariant

Page 13: Auditory perception classes: critical bands/auditory filters

The auditory periphery

Page 14: Auditory perception classes: critical bands/auditory filters

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Human cochlea: 3-D reconstruction

Page 15: Auditory perception classes: critical bands/auditory filters
Page 16: Auditory perception classes: critical bands/auditory filters

Cochlear animation, the Hudspeth version

http://www.rockefeller.edu/labheads/hudspeth/movie06_popup.html

Page 17: Auditory perception classes: critical bands/auditory filters

Masking

• The interference one sound causes in the reception of another sound– Peripheral component/cause: overlapping excitation pattern– Central component/cause: uncertainty - “informational masking”

• Masking experiments have been used extensively to investigate spectral and temporal aspects of hearing– Masking to study frequency selectivity: the critical band– Forward and backward masking (temporal and spectral constraints)– Comodulation masking release CMR (‘unmasking’ of sub-threshold

signal by comodulated signal in different regime)

Page 18: Auditory perception classes: critical bands/auditory filters

Classic experiment: Fletcher 1940

Page 19: Auditory perception classes: critical bands/auditory filters

Bandlimited noise stimuli

Page 20: Auditory perception classes: critical bands/auditory filters

Classic experiment: Fletcher 1940

Schooneveldt & Moore 1989

Determine threshold of sinusoidal signal in noise.Noise always centered at signal frequency.

Frequency (Hz)

Sou

nd le

vel (

dB)

masker

signal

• ASA Demos 2-6 -- count tones in noise, as function of bandwidth.• Increases in noise bandwidth result in more noise passing through a given filter, yielding more masking. However, when the noise bandwidth exceeds the filter bandwidth, there is no more threshold change. The point at which further increases yield no further threshold in creases: critical band. • Starting with Fletcher, masking studies have been used to evaluate frequency selectivity of auditory system.• Interpretation of masking data: auditory periphery can be described as a set of contiguous, overlapping bandpass filters, with overlapping passbands. These “auditory filters” comprise the first stage in the spectro-temporal analysis of all sounds.

Page 21: Auditory perception classes: critical bands/auditory filters

Critical bands by loudness comparison

frequency

lou

dn

ess

Reference noise band compared to test noise band with increasing bandwidth (constant power).When the bandwidth of the test noise exceeds the critical bandwidth, the loudness begins to increase.(ASA Demo 7)

Zwicker & Feldtkeller 1967; Scharf 1970; Rossing 1982

Page 22: Auditory perception classes: critical bands/auditory filters

Model of masking: Power spectrum model1. The (peripheral) auditory system contains an array of linear overlapping bandpass filters.2. When detecting signal in noise, listener makes use of just one filter, centered close to the

signal frequency. This filter will pass the signal but remove a great deal of the noise.3. Only the noise components passing through the filter will mask the signal.4. The threshold is determined by the amount of noise passing through the filter. The threshold

corresponds to some signal-to-noise ratio K at the output of the filter.

• Simplifying assumption made by Fletcher: rectangular filters, ‘flat top’, width of the filter is CB.• Estimate value of CB indirectly by measuring power of sinusoidal signal Ps required for

detection in broadband white noise of power density N0.

Noise falling within CB is N0 x CB. Following 4 above, Ps/(N0 x CB) = K

CB = Ps/(N0 x K)

By measuring Ps and N0 and estimating K, the value of the critical band can be determined.(Fletcher estimated K=1; Scharf, 1970, revised that to about 0.4) (Ps/N0 called ‘critical ratio’)

Estimating the shape of the auditory filter based on power-spectrum model:

Ps = K 0

N(f) W(f) df

• Masker is represented by its long-term power spectrum N(f)• Weighting function, or auditory filter is W(f)• Ps is power of the signal at threshold

Page 23: Auditory perception classes: critical bands/auditory filters

To assess auditory filter shape, Roy Patterson developed a new masking approach. The signal is fixed in frequency and the masker is noise with a bandstop, the width of which is varied.Threshold corresponds to a constant signal-to-masker ratio at the output of the filter.

Patterson, R.D. (1976). J. Acoust. Soc. Am., 59, 640-659.

Patterson’s ‘notched noise’ method

Page 24: Auditory perception classes: critical bands/auditory filters

Patterson, R.D. (1974). J. Acoust. Soc. Am., 55, 802-809.

Patterson’s ‘notched noise’ method

Page 25: Auditory perception classes: critical bands/auditory filters

Shape of auditory filter from notched noise

The auditory filter, unsurprisingly, is unlike a simple rectangular filter. This filter cannot be specified with a single number … However, some sort of summary statistic is useful. Common measure: bandwidth of the filter at the point at which the power has fallen by a factor of 2 -- i.e. by 3 dB. (Other measure: equivalent rectangular bandwidth (ERB)).

Other approaches to characterizing the auditory filter:• psychophysical tuning curves (e.g. Vogten 1974)• rippled noise method (Glasberg, Moore, Nimmo-Smith 1984 )

Typical values of auditory filter bandwidth, based on notched-noise approach: 10-15% of center frequency.

Page 26: Auditory perception classes: critical bands/auditory filters

Psychophysical tuning curves

Page 27: Auditory perception classes: critical bands/auditory filters

• A critical band CB is understood as a spectral window over which energy is integrated for certain tasks.

• Spectral band filters, as observed in psychoacoustics and in behavioral experiments, are sliding spectral windows.

• CB estimates in humans are ~0.14 - 0.23 octaves

Four approaches to study critical bands

1. Masking with noise on target

2. Critical bands by loudness

3. Notched noise method

4. Psychophysical tuning curves

Page 28: Auditory perception classes: critical bands/auditory filters

The width of the critical band (auditory filter) changes with center frequency

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The shape of the critical band (auditory filter) changes with signal amplitude

Page 30: Auditory perception classes: critical bands/auditory filters

Relation between auditory filters and excitation pattern

Top: 1-kHz sinusoid as ‘represented’ by five auditory filters, centered at different frequencies.

Bottom: calculated excitation pattern of auditory system

Moore & Glasberg 1983

Page 31: Auditory perception classes: critical bands/auditory filters

Summary 1: The filter-bank model of hearing

• The basilar membrane 'filters' parts of a sound into the auditory-nerve fibers, so that the output of the cochlea is like the output of a bank of filters that transmit information in parallel. • Each of these 'auditory' filters is centered at a different frequency, and responds to only a narrow range of frequencies. The centre frequencies of adjacent filters are very close, so that their frequency ranges overlap considerably. • There are around 25,000 nerve fibres in the auditory nerve, so the center frequencies of filters are, effectively, continuously distributed over the ear's frequency range.

Page 32: Auditory perception classes: critical bands/auditory filters

Hall & Garcia, 2012

1. Human auditory perceptual analysis is quantized into < 30 “critical bands” 2. of perceptually near-identical frequency analysis classes 3. corresponding to approximately equal length bands of cochlear tissue (receptor surface)

Summary 2: critical bands/auditory filters

basal end apical end

Page 33: Auditory perception classes: critical bands/auditory filters

Co-modulation masking release (CMR)Task: Detection of a pure tone embedded in noiseStimuli: Target & 2 types of noise

1) Gaussian white noise (UM)

2) Amplitude-modulated noise (CM) (Gaussian white noise x sinusoid)

amplitude

time

Co-modulated temporal

fluctuations across different frequency

bands

Page 34: Auditory perception classes: critical bands/auditory filters

Auditory CMR Stimuli presentation timeline & summary

Target

ISI = 500ms

ISI = 500ms

mask = 1000ms

target = 750ms

x 100 trials per condition per session x 3...

Task: Detection of a pure tone embedded in noiseStimuli: Target masked by either UM or CM noise

UM CMEach type of noise masker is filtered to have different bandwidths: typically: 50, 100, 200, 400, 1000, 2000 Hz (=12 blocks) centered at a given frequency (e.g., 1, 2 or 4 kHz)

Measure: thresholds for detection of target in each noise condition using interleaved staircases (2x 1-up, 2-down), 50 trials per staircase

Trials blocked by condition type

Page 35: Auditory perception classes: critical bands/auditory filters

Co-modulation masking release (CMR)

UM

CM

Critical Band width for 1 kHz Center Frequency

First reported in: Hall, J.W., Haggard, M.P. & Fernandez, M.A. (1984).  Detection by spectro-temporal pattern analysis.  J. Acoust. Soc. Am. 76: 50-56.

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Co-modulation masking release (CMR)

Page 37: Auditory perception classes: critical bands/auditory filters

Co-modulation masking release (CMR)

• Target detection is easier when the noise masker is amplitude co-modulated (CM) compared to the reference (UM) white noise condition.

• The CMR effect increases with increasing bandwidth (counterintuitive...adding more noise reduces threshold!)

• Proposed mechanisms (many): e.g., “the dip-listening hypothesis”

Summary

Page 38: Auditory perception classes: critical bands/auditory filters

Co-modulation masking release (CMR)

• The classical auditory CMR effect (typically run at 50Hz) can be obtained @ lower modulation frequencies...(extensive piloting done at 4Hz, 5Hz & 10Hz modulation frequencies). The above results are also reported in the literature: Bacon et al. (1997). Masking by modulated and unmodulated noise: effects of bandwidth, modulation rate, signal frequency, and masker level.

Page 39: Auditory perception classes: critical bands/auditory filters

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Spectral resolution is great.But do you always need it?Shannon 1995