[Long latency auditory evoked potentials: value of multichannel analysis and of high-resolution graphic mapping]

Auditory Evoked Potentials maps (AEP) were computed from 32 simultaneously recorded channels over both hemispheres using a linear interpolation algorithm. Reference electrode was extracephalic. Stimulus was a 781 Hz tone (intensity 70 dB HL, duration 256 msec). Average AEP were from 128 responses to randomly delivered stimuli. Direct current and frequencies over 50 Hz were removed by means of a digital filter (FFT). Results from 15 subjects showed before 120 msec a symmetrical response of AEP at vertex with left ear, right ear or binaural stimulation. Between 120 and 170 msec, maps of evoked responses were asymmetrical showing greater potentials over temporal areas contralateral to the stimulated ear.