Our results have implications for differential activation of structures in the pursuit system when large vs. small objects are pursued. When the main stimulus for pursuit is small and attention is directed toward it to drive pursuit, potential structures that are preferentially activated are the superior colliculus (SC), which processes position error (Krauzlis, Basso, & Wurtz,
2000), and possibly pursuit areas in frontal cortex that are not part of the classic motion processing pathway, such as the frontal eye fields (FEFs; Gottlieb, Bruce, & MacAvoy,
1993; MacAvoy, Gottlieb, & Bruce,
1991; Shi, Friedman, & Bruce,
1998; Tanaka & Lisberger,
2001) and the supplementary eye fields (Heinen,
1995; Lee & Tehovnik,
1995; Missal & Heinen,
2001; Schlag & Schlag-Rey,
1987; Schlag, Schlag-Rey, & Pigarev,
1992). In the current experiments, we supplemented the small stimulus that is normally foveated during pursuit with a large RDC that also stimulated peripheral retina. Since our results suggest that the RDC minimizes the necessity to attend to the spot in order to pursue, position error that develops between it and the fovea may be irrelevant for maintaining pursuit, and therefore, pursuit regions that are more specifically involved in processing motion might be preferentially activated when the RDC is present. These would include the main cortical motion areas that have been implicated in pursuit, including the middle temporal area (MT) and the medial superior temporal area (MST; Dürsteler & Wurtz,
1988; Newsome, Wurtz, & Komatsu,
1988). Also activated might be subcortical structures in the accessory optic system, such as the nucleus of the optic tract (NOT), that have been implicated in pursuit, peripheral motion processing and the more reflexive optokinetic reflex (OKR; Hoffmann & Distler,
1989; Ilg, Bremmer, Hoffmann,
1993; Inoue, Takemura, Kawano, & Mustari,
2000; Mustari & Fuchs,
1990).