Auditory event related potentials were recorded in 80 normal subjects (37 males and 43 females) aged from 10 to 81 years on an oddball task. The stimulus was a pure tone delivered binaurally at 75 dB SPL with a frequency of 1 kHz (frequent 80%) or 2 kHz (rare, target 20%). The subjects responded to target stimuli either by counting or by pressing a button. EEG was recorded from Cz and Pz referred to linked mastoids. The period from the tone delivery to the button-pressing was recorded and it was defined as the reaction time. The mean (RT) and the standard deviation (SD) of the reaction time were calculated.
The SD was interpreted to indicate the concentration of the subjects on the task. Results were as follows. The count condition may reflect aging more than the button-pressing condition. The N200 is related with the cognition of the stimulus more directly than the P300. The latency of P300 increased with age at a rate of 1.04 msec/year for count condition and 0.989 msec/year for button condition. The amplitude of P300 is more influenced by the concentration of subjects on the task than by aging.