Evoked potential correlates of selective attention with multi-channel auditory inputs.

Ten subjects were presented with a random sequence of 50 msec tone pips at a rapid rate (averaging one tone every 225 msec). The tones came from four different sound sources or sensory "channels" each having a different pitch (2000,4000,1000, and 500 c/sec respectively) and perceived spatial position (spaced equidistant across the head). Within each sensory "channel" a random 10% of the tones were of a slightly higher pitch (designated as "targets"). The subject attended to one channel at a time for 7.5 min and counted the targets in that channel. The auditory evoked vertex potential elicited by a channel of stimuli when attended was compared with the mean vertex potential elicited by those same stimuli when the other three channels were being attended. The N1 component (latency 80130 msec) measured re a baseline revealed an increase with attention (82% in the baselineN1 measure, P less than 10-). It was concluded that: (1) this N1 enhancement could not be attributed to peripheral mechanisms acting on sensory transmission; (2) this N1 enhancement reflects a "finely tuned" selective attention to one channel of stimuli among several concurrent and competing channels; and (3) a probable relationship exists between the information load on the subject and the magnitude of this EP enhancement with selective attention.