A possible reason for the observed sensitivity difference between fixation and smooth pursuit in our data is the concentration of spatial attention on the pursuit target to the detriment of perceptual performance in the periphery. Van Donkelaar (
1999) and Van Donkelaar and Drew (
2002) showed that the attentional focus is located slightly in front of the pursuit target during SPEM. Further evidence for an involvement of attention during SPEM comes from research on patients suffering from schizophrenia. These patients show impaired shifts of covert attention (Sereno & Holzman,
1996) as well as reduced pursuit gain (Kathman, Hochrein, Uwer, & Bondy,
2003), suggesting a connection between SPEM and attention. Kerzel and Ziegler (
2005) observed a similar difference in memory performance during SPEM and fixation. Subjects had to memorize the position of elements presented either in the fovea or in the periphery. Performance for peripheral presented elements was worse during SPEM compared to fixation; performance for foveally presented elements was equal during SPEM and fixation. The other way round, the influence of divided attention on SPEM is currently unclear in the recent literature. Chen, Holzman, and Nakayama (
2002) and Hutton and Tegally (
2005) showed that a demanding secondary task leads to impaired SPEM. On the other hand, two other studies (Kathman, Hochrein, & Uwer,
1999; Van Gelder, Lebedev, Liu, & Tsui,
1995) observed improved SPEM in a dual task paradigm. It may be that difficult secondary tasks impair, whereas easy secondary tasks facilitate smooth pursuit (Hutton & Tegally,
2005). Garbade and Deubel (
2002) showed that a moving distractor influences pursuit velocity. Distractors on the pursuit trajectory were more influential than distractors off the pursuit trajectory, which is an additional indicator for the allocation of attention to the pursuit target.