Scalp potentials following sudden coherence and discoherence of binaural noise and change in the inter-aural time difference: a specific binaural evoked potential or a "mismatch" response?
When uncorrelated random noise signals presented to the two ears suddenly become identical (coherent), a centrally located sound image is abruptly perceived and long latency scalp potentials are evoked. When the same signals are presented monaurally there is no perceived change and no potentials are evoked: hence the response must be purely a function of the binaural interaction. P70, N130 and P220 components were consistently recorded to both coherence and discoherence. N130 was usually largest at Fz and P220 at Cz. No potentials of shorter latency were identified, even after averaging 5000 or more sweeps. When the noise became coherent with an inter-aural time difference (delta T) of +/- 0.5 msec (giving rise to an off-centre sound image), the responses were of slightly longer latency and showed no significant asymmetries between C3 and C4. In binaurally coherent noise, delta T changes of +/- 0.5 or +/- 1.0 msec evoked similar responses which showed no significant asymmetries on the scalp. N130 was of longer latency when delta T was changed from +/- 0.5 msec to zero, as compared with the converse change. In view of the similarity of all these responses it is considered unlikely that they were due to specific populations of binaurally responsive cortical neurones. The N130 and P220 components are thought to be non-specific potentials which are elicited by any perceptible change in steady auditory stimulus conditions, due to a "mismatch" between the stimulus and the contents of a short-term auditory memory.
Jones
S J
SJ
National Hospital for Nervous Diseases, London, U.K.
Pitman
J R
JR
Halliday
A M
AM
D000161:Acoustic Stimulation; D000328:Adult; D004569:Electroencephalography; D005072:Evoked Potentials, Auditory / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D011930:Reaction Time; D012535:Scalp / Q000502:physiology*