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replaced with neurons that are excited by action potentials from one ear, but inhibited by action potentials from the other. However, EC theory is not generally framed in such explicit neurological terms, and no suitable neural substrate has been identified in the brain. Nonetheless, EC theory has proved a very popular modelling framework, and has fared well in direct comparison with cross-correlation models in psychoacoustic experiments
42:(dB) at 250 Hz and progressively declines to 2-3 dB at 1500 Hz. The BMLD then stabilises at 2-3 dB for all higher frequencies, up to at least 4 kHz. Binaural unmasking can also be observed for narrowband masking noises, but the effect behaves differently: larger BMLDs can be observed and there is little evidence of a decline with increasing frequency.
196:, which would allow the listener to gain an intelligibility improvement by simply listening to that ear. However, the interaural time differences can only be exploited by comparing the waveforms at the two ears. Successful models of spatial release from masking tend to use equalization-cancellaton theory to generate the effects of interaural time differences.
159:
occurs in which the resultant amplitude and phase differ from those of the noise or signal alone. For a binaural unmasking stimulus, the differences between the interaural parameters of the signal and noise mean that there will be a different vector summation at each ear. Consequently, regardless of
73:
A systematic labelling system for different stimulus configurations, first used by
Jeffress, has been adopted by most authors in the area. The condition names are written NxSy, where x is interaural configuration of the noise and y is the interaural configuration of the signal. Some common values for
141:
from the two ears via a network of axons that introduce differential transmission delays. Detection of a signal is thought to occur when the response rate of the most active coincidence detector is reduced by the presence of a signal. Cross-correlation of the signals at the two ears is often used as
34:
compared to a reference situation in which the interaural phases are the same, or when the stimulus has been presented monaurally. Those two cases usually give very similar thresholds. The size of the improvement is known as the "binaural masking level difference" (BMLD), or simply as the "masking
145:
The subtractive account is known as "equalization-cancellation" or "EC" theory. In this account, the waveforms at the two ears (or their internal representations) are temporally aligned (equalized) by the brain, before being subtracted one from the other. In effect, the coincidence detectors are
154:
The ear filters incoming sound into different frequencies: a given place in the cochlea, and a given auditory nerve fibre, respond only to a limited range of frequencies. Consequently, researchers have examined the cues that are generated by mixtures of speech and noise at the two ears within a
61:, which varies with the direction of a sound source and is involved in sound localisation. The fact that speech can be unmasked and the underlying cues vary with sound direction raised the possibility that binaural unmasking plays a role in the
179:
In everyday life, speech is more easily understood in noise when speech and noise come from different directions, a phenomenon known as "spatial release from masking". In this situation, the speech and noise have distinct
30:. The phenomenon is most commonly observed when there is a difference between the interaural phase of the signal and the interaural phase of the noise. When such a difference is present there is an improvement in
167:
Experiments have examined which of these cues the auditory system can best detect. These have shown that, at low frequencies (specifically 500 Hz), the auditory system is most sensitive to the
184:
and interaural level differences. The time differences are produced by the differences in the length of the sound path to the two ears and the level differences are caused by the
142:
mathematical surrogate for modelling such an array of coincidence detecting neurons; the reduced response rate is translated into a reduction in the cross-correlation maximum.
192:, and have both been shown to have independent effects in spatial release from masking. The interaural level differences can give rise to one ear or the other having a better
471:
697:
Beutelmann R, Brand T (2006). "Prediction of speech intelligibility in spatial noise and reverberation for normal-hearing and hearing-impaired listeners".
38:
Binaural unmasking is most effective at low frequencies. The BMLD for pure tones in broadband noise reaches a maximum value of about 15
125:
The cross-correlation account relies on the existence of a coincidence detection network in the midbrain similar to that proposed by
122:
Binaural unmasking has two main explanatory frameworks. These are based on interaural cross-correlation and interaural subtraction.
26:. In binaural unmasking, the brain combines information from the two ears in order to improve signal detection and identification in
559:"Interaural correlation fails to account for detection in a classic binaural task: Dynamic ITDs dominate N0SĪ detection"
107:Ī means that the noise has an interaural correlation of less than one, the exact correlation being specified elsewhere.
399:
Colburn HS (1977). "Theory of binaural interaction based on auditory-nerve data. II. Detection of tones in noise".
181:
168:
130:
97:
58:
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Culling JF (2007). "Evidence specifically favoring the equalization-cancellation theory of binaural unmasking".
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Licklider JC (1948). "The influence of interaural phase relations upon the masking of speech by white noise".
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171:. At higher frequencies, however, there seems to be a transition to using interaural level differences.
62:
57:. Licklider noted that a difference in interaural phase that was being used in unmasking is similar to
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658:"The effect of head-induced interaural time and level differences on speech intelligibility in noise"
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515:
408:
373:
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McFadden D, Pasanen EG (1978). "Binaural detection at high frequencies with time-delayed waveforms".
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Durlach NI (1963). "Equalization and cancellation theory of binaural masking-level differences".
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Hirsh IJ (1948). "The influence of interaural phase on interaural summation and inhibition".
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narrow frequency band around the signal. When a signal and narrowband noise are added, a
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Jeffress LA, Blodgett HC, Sandel TT, Wood CL (1956). "Masking of Tonal
Signals".
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the level and phase differences of the stimuli at the listener's ears.
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u means that the signal or noise is uncorrelated across the two ears.
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means that the signal or noise has an interaural phase difference of
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248:
Hirsh IJ, Burgeat M (1958). "Binaural
Effects in Remote Masking".
50:
27:
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Jeffress, L.A. (1948). "A Place Theory of Sound
Localization".
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0 means that the signal or noise is identical at the two ears
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the stimulus construction, there tend to be fluctuations in
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effect of the head. These two cues play a major role in
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22:is phenomenon of auditory perception discovered by
137:. Each coincidence detector receives a stream of
100:, where the exact value of the time difference,
113:m means that the signal or noise is monaural.
8:
359:
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608:"Subcomponent cues in binaural unmasking"
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96:means that the signal or noise has an
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557:Van Der Heijden M, Joris PX (2010).
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656:Bronkhorst AW, Plomp, R (1988).
129:to account for sensitivity to
16:Auditory perception phenomenon
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182:interaural time differences
169:interaural time differences
131:interaural time differences
45:Improved identification of
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98:interaural time difference
59:interaural time difference
575:10.1007/s10162-009-0185-8
104:, is specified elsewhere.
563:J Assoc Res Otolaryngol
175:Practical implications
53:was first reported by
194:signal-to-noise ratio
63:cocktail party effect
711:2006ASAJ..120..331B
627:2011ASAJ..129.3846C
606:Culling JF (2011).
520:2007ASAJ..122.2803C
413:1977ASAJ...61..525C
378:1956ASAJ...28..416J
340:1948ASAJ...20..150L
297:1978ASAJ...63.1120M
262:1958ASAJ...30..827H
227:1948ASAJ...20..536H
35:level difference".
444:J. Acoust. Soc. Am
401:J. Acoust. Soc. Am
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285:J. Acoust. Soc. Am
250:J. Acoust. Soc. Am
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190:sound localisation
186:acoustic shadowing
135:sound localization
20:Binaural unmasking
719:10.1121/1.2202888
635:10.1121/1.3560944
528:10.1121/1.2785035
456:10.1121/1.1918675
386:10.1121/1.1908346
348:10.1121/1.1906358
270:10.1121/1.1909781
235:10.1121/1.1906407
139:action potentials
127:Lloyd A. Jeffress
74:x and y include:
32:masking threshold
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479:(1): 35â9.
200:References
24:Ira Hirsh
741:Category
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643:21682408
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544:24476950
536:18189570
493:18904764
118:Theories
40:decibels
707:Bibcode
684:3372866
623:Bibcode
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162:both
715:doi
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579:PMC
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