Selection of speech messages in free-field listening

Event-related brain potentials (ERPs) elicited by initial consonants of words in a spoken message were recorded from 10 human subjects. In an ecologically valid free-field situation, brain responses to speech were recorded for the first time without using artificial probe stimuli as ERP trigger signals. In an analogy to a 'Cocktail-Party' situation in its most elementary form, two concurrent stories were delivered via separate left and right loudspeakers. The subject's task was to selectively attend to a designated message while ignoring the other. Results show a very early attention effect for a speech message commencing at about 40 ms from stimulus onset. This early effect appears to be based on tonic facilitation of the attended message and contextual cues.