INTERTARGET INTERVAL DOES NOT AFFECT P300 WITHIN ODDBALL SERIES

Increasing interstimulus interval or decreasing target probability of an oddball series increases P300 amplitude. These findings serve as on e of the key underpinnings for the context updating hypothesis of P300 . This hypothesis argues that by increasing the average amount of time elapsing between targets, decay of the neural model occurs and there is greater need for updating the model's accuracy. The amount of updat ing is reflected by increased P300 amplitude. To date, most comparison s have been made between P300 elicited by targets in different oddball series which vary in their mean intertarget interval. The current stu dy examined P300 responses to within-series targets grouped according to how much time had elapsed since the previous target. No differences were found between P300 responses elicited by targets occurring 5-20 s since the previous target. This indicates that P300 amplitude does n ot vary with the amount of time passing between targets. Therefore, th e context updating hypothesis may require some revision.