SPECIAL ISSUE DISSOCIATING ASPECTS OF TEMPORAL AND FREQUENCY PROCESSING: A FUNCTIONAL ERP STUDY IN HUMANS Henning Gibbons, Susanne Brandler and Thomas H. Rammsayer (Georg Elias Müller Institute for Psychology, University of Göttingen, Germany) ABSTRACT An event-related potential (ERP) study was conducted, in order to dissociate brain functions associated with temporal information processing and processing of frequency information. Twelve participants were presented with both a temporal generalization and a pitch generalization task. In both tasks, exactly the same set of stimuli was presented to prevent stimulus-specific influences on ERP patterns. Participants had to decide whether or not an auditory stimulus matched a previously memorized standard stimulus, either with respect to pitch or duration. Analysis of ERPs revealed an increased negativity for the temporal discrimination task at fronto/central electrode sites. This effect was observed between 150 msec and 1,000 msec. At posterior sites, however, there was an increased positivity between 500 and 1,000 msec for the temporal generalization task. The differential topological activation patterns suggest more pronounced utilization of executive working- memory ressources for processing of temporal than for processing of pitch information. Key words: duration, frequency, ERP, working memory, temporal processing INTRODUCTION Duration represents a stimulus dimension inherent in any stimulus, while, at the same time, duration cannot be perceived if a given stimulus does not consist of another additional stimulus dimension, such as intensity, frequency, or color. This phenomenon is due to the fact that there is neither a specific receptor system nor a specific receptor energy for temporal information. Thus, to process temporal characteristics of a stimulus, non-temporal stimulus information is necessary in order to perceive an event to be timed (Gibson, 1975). Since time is not a perceptual dimension but a derived entity (Gibson, 1975; Michon, 1990; Rammsayer, 1992), an important question is whether processing of temporal information differs from processing of other stimulus dimensions present in the same stimulus. Although it is well established that distinct cortical areas are activated while processing specific stimulus dimensions such as shape, color, or intensity (Belin et al., 1998; Cabeza and Nyberg, 1997; Corbetta et al., 1990; Zeki et al., 1991), data on processing of temporal information are relatively scant and much more inconsistent. Several event-related potential (ERP) studies suggested that temporal processing of durations primarily involves the prefrontal cortex (Bruder et al., 1992; Casini and Macar, 1993; Elbert et al., 1991; Johannes et al., 1997). Cortex, (2003) 39, 947-965