Abstract: The Simon effect refers to the fact that responses are faster when the stimulus location corresponds to the location of the assigned response than when it does not, which is a robust phenomenon. However, practicing with an incompatible mapping from location to responses can eliminate or even reverse a subsequent Simon effect. But, it is still unclear about how the acquired incompatible association was represented in the working memory (WM). In the present study, we conducted two experiments to investigate this question through using practice-transfer design combined with dual-task paradigm. Subjects first received sufficient practice with an incompatible mapping from location to response, i.e., pressing right key to left stimulus or left key to right stimuli, then were randomly transferred to the single task (only Simon task) or one of two dual-tasks (concurrent spatial WM load + Simon tasks; concurrent verbal WM load + Simon tasks) 5 minutes later.
In Experiment 1, the dual-tasks were traditional configuration: the stimuli of the verbal WM load task were true Chinese characters, and the stimuli of the spatial WM load task were pseudo-characters. In the two dual-tasks, Subjects were asked to memorize the four locations or the seven characters, and they expected to have a recognition test after having completed the Simon tasks. If the probe was in the same location as one of the pseudo-characters or identical to one of the seven characters presented in the memory display, subjects were to press the “1” key with the left middle finger. Otherwise, they were to press the “0” key with the right middle finger, and the proportions of the two responses were 50% and 50%, respectively. The results showed a reversal Simon effect in the single task, which is consistent with previous findings. Importantly, the results showed that the verbal WM load eliminated the reversal Simon effect, but the spatial WM load had no influence on the reversal Simon effect.
However, the employment of Chinese characters in the verbal WM load task could be problematical, since it has been demonstrated that Chinese characters may engage spatial processing in addition to verbal processing; on the other hand, pseudo-characters may have some linguistic properties. Therefore, it is premature to conclude that the acquired associations are represented as verbal codes in WM. In order to address the limitations of Experiment 1, in Experiment 2, the stimuli of WM load task were the Chinese characters presented through auditory modality in the verbal WM load task and the pseudo-characters were replaced with black filled squares. The characteristics of these stimuli may ensure that the verbal WM load and spatial WM load occupied the phonological loop and the visuospatial sketchpad of the working memory, respectively. The results showed significant reversal Simon effects in the spatial dual-task, but no normal or reversal Simon effect was observed in the verbal dual-task, which perfectly accords with Experiment 1. Hence, we can confirm that the acquired associations are represented as verbal codes in WM. Straightforwardly, the present study strongly suggested that the transfer of acquired associations relies on the verbal working memory.

Key words: Simon effect, transfer of location associations, working memory, verbal codes