Multitasking: The Impact of Spatial and Verbal Working Memory on the Simon Effect

The Simon effect occurs when a person’s reaction time to a stimulus feature such as color is quicker and more accurate when the stimulus occurs in a location that corresponds with the physical response rather than one that does not. For example, if a red circle appears on the right side, the response is the faster when red is assigned to a right physical response than when it is assigned to a left physical response. This effect of irrelevant stimulus location is presumed to be a consequence of having the spatially defined responses active in working memory (WM). Zhao, Chen, and West (2010) studied the influence of WM on this phenomenon using simple spatial or verbal exercises called memory loads. Requiring participants to maintain a verbal memory load eliminated the Simon effect, but requiring them to maintain a spatial memory load had no influence on it. My study was designed to replicate and extend Zhao et al.’s study. The only differences were that the participants were from the United States rather than China, and the verbal material was English letters rather than Chinese characters. Experiment 1 showed that I was able to obtain the Simon effect in a baseline condition for which there was no memory load. In Experiment 2, prior to each trial of the Simon task, participants were presented a set of four letters or four locations of a grid, which they were to remember for a memory test given after making the response for the Simon task. With this method, the working memory loads in the two conditions were more comparable than in Zhao et al.’s study. Results show that the Simon effect was eliminated during the spatial task but not during the verbal task. Possible reasons for the discrepancy between my results and those of Zhao et al. are the demographic background of participants and the stimuli used for the studies. Knowing conditions under which irrelevant location correspondences influence performance is important for design of human-machine interfaces that enable fast and accurate operation