Abstract
The effects of attention on P300 from the auditory three-stimulus oddball tasks were examined. Twelve undergraduate students participated in three tasks. They were required to press a button to respond to the tar-get stimuli in an active task, while in an ignore task, they engaged themselves in another visual task. In a passive task, the subjects were given no special instructions about the stimulus sequences. Target (p =.15), standard (p =.70), and infrequent nontarget (p =.15) stimuli in a 'novels' condition were 2000 Hz tone, 1000 Hz tone, and 36 different novel sounds, and in a 'tones' condition, a novel sound, another novel sound, and 36 different tones which differed in frequency ranging from 523 to 3951 Hz, respectively. In the active task, target stimuli elicited P3b in both conditions. In addition, rare nontarget novel sounds elicited novelty P300 ('novels' condition), although rare nontarget tones elicited P3b ( 'tones' condition). In contrast, in the ignore and passive tasks, small P300 emerged only for the novel sounds in the 'novels' condition. The results suggest that when subjects do not pay attention to the stimulus sequences, the 'novel' characteristic of the rare stimuli in tone sequence are necessary for those stimuli to capture subject's attention.
