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General definitions of attention usually include reference to the speed, efficiency, or depth of processing, with the prediction that attended stimuli are processed more quickly, efficiently, and deeply than unattended stimuli (Sternberg, 1999). Within the field of attention research, one important distinction is between selective attention and divided attention. Selective attention requires a subject to selectively process (focus attention on) one of several possible stimuli, whereas divided attention requires a subject to coordinate the processing of multiple sources of information.

To assess divided attention, many researchers have used what are typically referred to as dual-task paradigms (Johnston et al., 1995; Pashler, 1993). Dual-task paradigms involve the concurrent performance of two tasks that vary in complexity. The extent to which the tasks interfere is taken as a measure of the extent to which the two tasks involve common processes (or shared attentional resources). Studies of divided attention using dual-task paradigms have addressed a range of questions, including the types of stimuli or tasks that interfere with one another, the likely site of dual-task interference (in terms of stage of information processing), and under what conditions (e.g., sleep deprivation, drug influence, general fatigue) attention is most impaired (Pashler and Johnston, 1998). The focus of this chapter is on the role of frontal cortical areas in divided attention and simultaneous temporal processing (STP).

Simultaneous temporal processing refers to the concurrent performance of two or more timing tasks. For example, subjects in a typical STP task might be asked to simultaneously reproduce two different durations, each associated with a different cue (e.g., light or tone). Interval timing tasks have often been incorporated into studies of divided attention because timing performance is sensitive to different types of behavioral and neurobiological manipulations of attention (Macar et al., 1994; Meck, 1996; Meck and Williams, 1997; Olton et al., 1988). The primary goal of this chapter is to explore some ideas about the neurobiology of timing and divided attention within the context of the STP paradigm. Toward this end, we provide evidence for neural correlates of divided attention obtained from single-cell recordings of the frontal motor cortex of the rat.

The chapter is divided into three sections. First, we review relevant theory and data on short-interval timing. Next, we consider the role of frontal cortical areas in divided attention within the context of information-processing theories of timing. Finally, we describe a recent electrophysiological study from our lab that supports the idea that neurons in the frontal motor cortex are directly involved in divided attention. We then consider some alternative interpretations of these data and suggest some directions for future research.

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