INFLUENCE OF REFERENCE ELECTRODES, STIMULATION CHARACTERISTICS AND TASK PARADIGMS ON AUDITORY P50

To clarify the nature of auditory P50, middle latency auditory evoked potentials were recorded by using different conditions of reference el ectrodes (linked earlobes, LE; balanced non-cephalic, BN), stimulation characteristics (tone burst, human voice) and tasks (counting, simple reaction) in 10 right-handed males (aged 21-36 years). EEG was record ed from Fz, Ct, Pt, C3, C4, T3 and T4 according to the 10-20 system. T wo groups of electrode sites were made for the statistical analysis: a midline group, Fz, Ct and Pt; and a lateral group, T3, C3, Cz, C4 and T4. The results were that the P50 amplitudes with BN electrodes were significantly higher than those with LE in both groups (midline, P < 0 .01; lateral, P < 0.01); the P50 amplitudes by voice stimulation were significantly higher than those by tone stimulation in the lateral gro up (P < 0.05), and the P50 latencies under a simple reaction paradigm were significantly shorter than those under a counting task in both gr oups (midline, P < 0.05; lateral, P < 0.05). These results suggest tha t various factors including motor response affect the P50 amplitudes a nd latencies.