Although other studies have reported specificity of training benefits between tasks limited by cognitive control mechanisms, (Gaspar, Neider, Simons, McCarley, & Kramer,
2013; Melby-Lervåg & Hulme,
2013; Thompson et al.,
2013), to our knowledge we are the first to demonstrate such minimal generalization of large training benefits between nearly identical attention-limited tasks (all tasks required tracking two moving targets) that were shown to require a common attentional capacity (see
Appendix A1). Because of this specificity, we claim that training enhances content-specific attentional coordination rather than general attentional capacities, a conclusion that assumes the attentional tracking tasks in this study use and are limited by the same attentional mechanisms. This assumption can be supported in several ways. First, we ran a preliminary study using the attentional operating characteristic method (see
Appendix A1), demonstrating a performance tradeoff between the tasks that is evidence of a common attentional capacity. In previous studies failing to find generalization following training, it is often unclear whether the training and transfer tasks rely on the same capacity [particularly in studies training working memory, which appears to have separate capacities for visual vs. verbal information (Baddeley & Hitch,
1974), visual vs. spatial information (Wood,
2011), and view-dependent vs. view-invariant information (Wood,
2009)]. Second, previous research has suggested that objects tracked within a single visual hemifield (left or right) are maintained by a common attentional resource (Alvarez & Cavanagh,
2005); in the present study, the trained and untrained tasks always occurred within the same visual hemifield. Third, neuroimaging research has implicated the intraparietal sulcus as a critical region across a variety of attentional tracking tasks, including translational (Culham et al.,
1998) and rotational motion (Shim, Alvarez, Vickery, & Jiang,
2009); baseline performance for the two types of motion was also highly correlated in our subjects (
Appendix A8). Finally, although using target speed as the study's dependent measure (rather than the number of items tracked) may intuitively seem to introduce low-level representational challenges to the tracking task (in addition to attentional limitations), previous research has indicated that observers have sufficient representational precision for tracking items at high speeds, yet are unable to access these representations efficiently when attention is divided (Alvarez & Franconeri,
2007). Furthermore, both the speed at which objects can be tracked and the number of objects that can be tracked appear to be limited by a common capacity (Thompson, Gabrieli, & Alvarez,
2010). Therefore, we are confident that tracking performance was primarily attention-limited in this study despite target speed being the dependent measure, and predict a similar pattern of results would occur if the number of targets were increased during training instead of target speed.