Abstract Although gaze direction conveys spatial information, its spatial coding properties remain unexplored. This study investigated distinct natures of spatial codes for each axis of gaze direction by examining the cross-task congruency sequence effect (CSE) and the time courses of the Simon effect. Participants performed horizontal and vertical Simon tasks alternatively in a trial-by-trial manner, using gaze direction and another spatial mode, respectively. Experiments 1a and 1b examined whether spatial codes for gaze direction vary by axis. Subsequent experiments examined whether horizontal and vertical gaze directions shared spatial codes with physical location (Experiment 2a and 2b), arrows (Experiment 3), and location words (Experiment 4a and 4b). The findings revealed that horizontal and vertical gaze directions exclusively shared spatial codes with different spatial modes. For the horizontal gaze-based Simon task, a cross-task CSE was found with the vertical arrow-based Simon task but not with the vertical gaze-based or vertical word-based Simon tasks. A unidirectional CSE was found from the vertical location-based Simon effect to the horizontal gaze-based Simon effect. In contrast, the vertical gaze-based Simon task showed a cross-task CSE only with the vertical word-based Simon task. Moreover, the gaze-based Simon effects and other modes of Simon effects revealed different patterns of time courses. Different shapes of delta functions reflected differences in the speed of activation and dissipation of spatial codes in the early stages of response processing but did not indicate qualitative differences in their spatial codes. These results suggest that horizontal and vertical gaze directions encode spatial information via different attributes.
Lee et al. (Thu,) studied this question.
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