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The Farnsworth-Munsell

To establish the stages of brain processing in an auditory stimulus localization task, event‐related potentials (ERPs) were recorded from 24 normal subjects listening to brief white noise stimuli in a free‐field situation from front, back, left and right loudspeakers. The subject's task was to respond to ‘target’ stimuli from one designated speaker. Performance varied as a function of sound location, stimuli in the front/back dimension being more difficult to localize than those in the left/right. ERP results, based on averaged waveforms, difference waveforms and the factors derived from a principal components analysis, revealed a series of task related components. Some were relatively transient, others more sustained in character. One brain component showed task related amplitude changes with an onset as early as 15 msec. These changes were target specific for sounds in the easier left/right dimension only. Later components, such as the P300, also varied in amplitude between targets and non‐targets, but showed no significant amplitude or latency differences to target stimuli as a function of location, despite the significant performance differences.

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