The effects of response sharing and stimulus presentation frequency on event-related potentials in an auditory oddball paradigm JA ´ NOS HORVA ´ TH, a URTE ROEBER, b and ERICH SCHRO ¨ GER b a Institute for Psychology, Hungarian Academy of Sciences, Budapest, Hungary b Institute of Psychology I, University of Leipzig, Leipzig, Germany Abstract An experimental model for investigating the processes involved in reacting to unpredictable events is the oddball paradigm. We investigated how the commonality or independence of response options (i.e., many-to-one vs. one-to- one stimulus-response mappings) influences processing in an auditory oddball paradigm. Participants performed a discrimination task with two one-to-one and one two-to-one mappings. The pattern of conflict- and oddball-related N2 event-related potentials suggest that information that would allow correct responding is represented at the latency of the N2. Integration of this information takes place only by the latency of P3b, and longer reaction times to rare stimuli are probably due to processes preventing the utilization of this information. We also suggest that, in the given task context, conflict-related N2 may reflect the number of alternative stimuli leading to alternative response options. Descriptors: Attention, Conflict, Oddball paradigm, Categorization, Event related potentials (ERP), N2, P3a, P3b Producing adequate reactions to unpredictable events occurring in the environment is crucial for the survival of the organism. An experimental model for investigating processes involved in such reactions is the oddball paradigm. In the oddball paradigm, reg- ular stimuli presented in a sequence are, occasionally, unpre- dictably replaced by irregular stimuli. Whereas most analyses of behavioral and event-related potential (ERP) responses in an oddball paradigm are concerned with the differential processing of frequent and rare stimuli, it is obvious that in many variations of the paradigm a comparison of behavioral and ERP responses to stimuli involves not only stimulus, but response differences as well. For example, rare stimuli may require a left-hand response, whereas frequent stimuli may require a right-hand response. Thus, right-hand responses are more frequent than left-hand re- sponses, and the stimulus frequency factor is perfectly con- founded with response frequency. Since stimulus-response associations are often one-to-one mappings, the separation of stimulus- and response-related effects is often problematic. One approach to separate the behavioral effects of stimulus-related and response-related processing is to utilize tasks with many-to- one instead of one-to-one stimulus-response (S-R) mappings, which makes it possible to separate stimulus- and response-fre- quency effects (see, e.g., Bertelson & Tisseyre, 1966). In the present study, we investigated how the commonality or inde- pendence of response options (i.e., many-to-one vs. one-to-one S-R mappings) influences processing in an auditory oddball paradigm. In the following, we briefly describe the ERPs typically elic- ited in active oddball paradigms, then we introduce two hypoth- eses regarding how response independence and commonality may influence these ERPs: 1) The first is based on the notion that stimulus-response events are represented in a combined network of stimulus and response features (event-files). Features shared between events result in processing interference, which suggests higher interference for stimuli mapped to the same response. 2) The second hypothesis is based on the idea that S-R map- pings prescribed by the given task influence the categorization of stimuli, and this imposed categorization influences stimulus processing. ERPs Elicited in Oddball Paradigms The sequence of processes triggered by infrequent stimuli in oddball paradigms has been widely studied using ERPs. In the present context, two components, the conflict-related N2 and the P3b, are the most important ones. Both components are elicited in active paradigms (i.e., in which participants perform a task on the stimulus sequence). This study was supported by the European Commission under the Marie Curie Intra-European Fellowship Project MEIF-CT-2006- 023924. The experiment was realized using Cogent 2000 developed by the Cogent 2000 team at the FIL and the ICN and Cogent Graphics developed by John Romaya at the LON at the Wellcome Department of Imaging Neuroscience. We thank two anonymous reviewers for con- structive comments on an earlier version of the manuscript. Address reprint requests to: Ja´ nos Horva´ th, Institute for Psychology, Hungarian Academy of Sciences, P.O.B. 398, Szondi u 83/85, H-1394 Budapest, Hungary. E-mail: horvath@cogpsyphy.hu Psychophysiology, 47 (2010), 931–941. Wiley Periodicals, Inc. Printed in the USA. Copyright r 2010 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2010.00990.x 931