Chronometry that combines ERP and reaction time was used to investigate the mechanism of stimulus discrimination and decision execution. The P300 latency is an index of stimulus classification speed. We investigate the effect of congruence visual stimuli and compatibility on ERP and reaction time. We hypothesized that congruency will affect stimulus evaluation and compatibility affect response selection.
The peak of P300 divided the reaction time into two section. P300 latency is the time for stimulus discrimination；The time from the peak of P300 to the initiation of movement is response selection. Subjects will respond by both hands under different conditions. Ours experiment had two parts. Experiment one used spatial code-「arrow」, experiment two used verbal code-「right & left」.
The results of experiment one showed that congruency and compatibility have significant effect on reaction time, so is the interaction. The results indicated that the two factors do not affect in parallel at different stages in the cognitive process. ERP results showed that compatibility did not change response selection time, and the effect of compatibility on P300 latency is depended on the congruence of the stimuli. P300 latency shows significant compatibility effect under congruent stimuli. The results of experiment two show that compatibility significantly increased the reaction time, response selection time, but not the P300 latency.
Brain may code the congruent and incongruent stimuli in different ways during the perceptual process. It seems that a bond may exist between the codes of congruent signals and motor “Engrams” and may affect perception and action planning. This bonding may explain why the P300 latency is longer under incompatible condition while receiving congruency stimulus. Compatibility and congruency are not independent on each other
