Task Switching Effects in Anticipation Timing

Switching between two or more actions is a fairly common occurrence that can be seen in a variety of settings. At work, people frequently switch between activities such as typing on a keyboard and dialing a telephone. At home, a person preparing dinner might switch between washing and chopping vegetables. In baseball, a pitcher switches between catching and throwing the ball. The effects of task switching have been extensively studied in the verbal domain (for a review see Monsell, 2003) using stimulus categorization tasks. In these types of tasks, stimuli are categorized according to specific rules governing the task sets that participants must perform. For example, the stimulus “G7” indicates that the participant should press the key corresponding to consonant for a letter task set (i.e., consonant vs. vowel) or to odd for a number task set (i.e., odd vs. even; Sohn & Anderson, 2001). As in this example, stimuli are frequently bivalent (i.e., used in both task sets), which creates response competition between the two task sets and makes switching difficult. The effects of task switching on stimulus categorization tasks have been well documented (Allport, Styles, & Hsieh, 1994; Jersild, 1927; Meiran, 1996; Rogers & Monsell, 1995; Spector & Biederman, 1976). Researchers have adopted the term switch cost to describe the typically observed increases in reaction time (RT) latencies or errors in a switched condition compared to a repeated condition. In this paper, the term switching effect will be used to refer to the more general influence of switching as an experimental manipulation. Much of the task switching literature has focused on determining the mechanisms underlying so-called residual costs that remain even after controlling for other costs related to incomplete preparation (i.e., inadequate time or response uncertainty; see for example, Allport et al., 1994; Altmann, 2002; Rogers & Monsell, 1995). Some evidence suggests that persisting activation carries over from one trial to the next and interferes with performance when the task is switched. Other evidence suggests that participants engage in executive control processes to manage the switch between competing tasks. As illustrated by the examples in the first paragraph, switching occurs across a wide variety of tasks, many of which involve motor performance. Little is known about how switching effects might generalize beyond the specific experimental procedures used to investigate them thus far (i.e., stimulus categorization). There are, however, some indications that switching influences the performance of tasks often studied in the motor domain. Hayes, Davidson, and Keele (1998) examined the performance of sequential movement tasks in repeated and switched conditions. The tasks required participants to press three keys arranged in an equilateral triangle. Movement was clockwise around the triangle for one task and counterclockwise for the other. Results indicated that performance was degraded when participants were required to switch from one sequence to the other compared to when they repeated the same sequence. It was unclear, though, whether the effect was due to switching, per se, because the task switch was confounded with a movement reversal. Other indications that switching might influence motor performance are found in research in which participants had to switch between tasks as part of the Task Switching Effects in Anticipation Timing