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KMID : 0376619920170020084
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Seoul Journal of Psychiatry
1992 Volume.17 No. 2 p.84 ~ p.96
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The Effects of Probability on P3 in Normal Subjects
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kwon Jun-Soo
Woo Jong-In
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Abstract
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Probability is known to determine the waveform of P3 elicited in odd-ball paradigm. The contribution of probability to the P3 was assessed at four levels of target stimulus probability (from 20% to 80%). Random sequences of high tone (2, 000Hz)
as target stimuli and low tone(1,000Hz) as non-target stimuli were presented to 13 male subjects at each level of probability with interstimulus interval of 1.03sed. The EEG was recorded from 21 scalp electrodes according to international 10-20 system. P3 was distinguished into P3a with latency range 220-300msec and P3b with 300-400msec and this phenomenon was prominent as the sites of electrodes goes to the posterior part of the scalp. The amplitue of target P3 was inversely proportional to the target stimulus probability. The latency of P3 in the condition of 20% target stimulus probability was relatively short compared to the P3 in the condition of 80% target stimulus probability. The location of electrodes had effect on the amplitudes and latencies of P3 regardless of the target stimulus probability. But at each level of probability, topographic effect on the amplitudes and latencies of the P3 was not found The correlation between the amplitude and the latency was not proven. The effect of the probability on the P3 was well demonstrated, but some findings like the topographic effect on the P3, the correlation between amplitude and latency was not consistent with the previous reports. These discrepancies can partly be due to our trial to divide P3 into P3a and P3b. We suggest that P3 be not unitary wave which indicate only one step in the information processing but complex waveforms which contains multiple components.
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